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Wood Veneer: Log Selection, Cutting, And Drying

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W 1.0 2.2 II~ 1111,1.25 111111.4 ~1111.6 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU or STANDARDS-1963-A '~N '. '~1:.. , • • <. . . . . " '.~. ~~ ;;~tfj~t:&if e • 1 WOOD VENEER: LOG SELECTION, CUTTING, AND DRYING ~ '-r ,. ( ) t,«- ( ":~ (~~ : .,. ro"i co r- 0") r...:.; t, ! (.- <,;;) c.~ C-" P) .:::r, :::> ().. ;.1­ :.:::i .2 n::::.! c:.t... m t",) nI::'J '" ;t"~,C u, ..9 Forest Service U.S. Department of Agriculture liP , ,-~':"" j Technical Bulletin No. 1577 Lutz, John F. 1977. Wood veneer: log selection, cutting, and drying. U.S. Dep. Agric., Tech. Bull. No. 1577, p. 137 Summarizes current information on cutting and drying veneer from many species of wood. Particular emphasis is placed on wood and log characteristics that affect veneer production; tech­ niques for peeling, slicing, and drying veneer; and species involved. KEYWORDS: Peeling, slicing, lathe, slicer, veneer quality, wood species, plywood, decorative panels, containers, thickness, physical properties, medlv.nical properties, grades. OxfNd No. 832.20 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. Stock No. 001-00~0372:J..·4. WOOD VENEER: LOG SELECTION, CUTTING, AND DRYING by John F'. Lutz, Technologist, Forest Products Laboratory, Forest Service, U.S. Department of Agriculture The Laboratory is maintained at Madison, Wis. in cooperation with the University of Wisconsin. Forest Service U.S. Department of Agriculture Technical Bulletin No. 1577 January 1978 PREFACE CUTtis Peters, Harry Panzf'l', Joe Clark, and John McMillen stand out. Other members of the Forest Service have been particularly helpful 'with information on wood species, especially John Putnam and those involved with surveys of the forest resources. From representative;:; of the wood industry have come advice, assistance, and encourage­ ment. The contributors are legion, with partic­ ular help from Tom Batey of the American Plywood Association and Bill Groah of Hard­ wood Plywood Manufacturing Association on many phases. In preparing this bulletin, the author relied heavily on three research publications he had written earlier. These three were published as U.S. Department of Agriculture Forest Sf'l"vice Research Papers, by the Forest Products Laboratory. These were: "Wood and Log Characteristics Affecting Veneer Production," by John F. Lutz, USDA Forest Service Research Paper FPL 150, 1971. "Veneer Species That Grow in the United States," by John F. Lutz, USDA Forest Seryice Research Paper FPL 167,1972. "Techniques for Peeling, Slicing, and Dry­ ing Veneer," by John F. Lutz, USDA Forest Service Research Paper FPL 228,1974. The broad spectrum of veneer cutting and handling for a multitude of uses obviously cov­ ers a wide range of operations by many special­ ists, and involves hard-learned secrE::ts. No one individual can be an expert in all areas-yet his efforts must be in line with those of others in research and industry. In these days of material shortages and pressure on energy sources, it seems doubly important to summa­ rize some of the principles and COOTdinate the terminology. This bulletin is a view of the art of veneer manufacture as seen by a specialist who spent the last 25 years in research and industry con­ tacts. It represents an attempt to tie together the experiences of many for the benefit of al1. Contributions to this web of information have come from literally hundreds of people throughout the United States. The references listed here represent noteworthy contributions, but only a few of them. Harder to document are the thoughts and philosophies that have been shared with the author over the last quar­ ter century. Outstanding among these have been the con­ tributions of other members of the Forest Products Laboratory staff. The research efforts and considered judgment of II. O. Fleischer, Use of trade, firm, or corp07'aticrIl names in this publication is f07' the infor­ mation and convenience of the 1·e(ulC'7·. Such use doC's not ('()nstitute all official endonlement 07' apP'1"ovnl of (my 7Jrodnct 07' sen·icC' by the U.S. Department of Ag7'iculture to the exclusion of othm's thnt 1na1l be sllitabll'. ii CONTENTS Page Introduction ·. ...................................................................................... 1 Wood and log characteristics affecting veneer production ............................................ . Veneer quality as related to end uses ............................................................. . Hardwoods or softwoC'ds for veneer .............................................................. . Physical properties of wood ...................................................................... . Mechanical properties of wood ................................................................... . Properties of veneer logs ........................................................................ . 1 2 2 3 12 12 Veneer from wood species that grow in the United States ................................. " . . . . . . . . . . . 21 Techniques :01' peeling, slicing, and drying veneer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Log storage ..................................................................................... Bark removal ................................................................................... Sawing into bolts or flitches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conditioning wood prior to cutting veneer ................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Veneer cutting equipment ........................................................................ Knife and pressure bar on lathe and slicer ................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conveying and clipping veneer .................................................................... Veneer drying . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Quality control .................................................................................. 29 29 30 31 34 45 54 69 70 75 Veneer yields and volume needed for a plant. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . Veneer yields (rotary cutting) .................................................................... Veneer yields (sliced) ............................................................................ Volume of timber needed to set up a veneer plant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 87 87 88 Literature cited ................................................................................... 89 Appendix I-Nomenclature of wood species and veneer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . 91 Appendix II-Physical properties of U.S. woods for veneer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Appendix III-Mechanical properties of U.S. woods for veneer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Appendix IV-Some processing variables of U.S. woods for veneer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 116 Appendix V-Effects of log storage and processing on veneer characteristics ........................... 121 Appendix VI-Appearance and suitability of individual U.S. species for various uses of veneer. . . . . . . . . . . . Glossary ......................................................................................... . 125 Index .............................................. " ..... . .. ... ...... .............. ......... ..... • Req1Lests for copies of illustrations contained in this pUblication shOUld be di1'ected to the Forest P1'oducts Labo1'at07'y, U.S. Del)artment of A.griculture, F'o1'est Se1'vice, P.O. Box 5130, Madison, Wis. 53705. iii 133 135 WOOD VENEER: LOG SELECTION, CUTTING, AND DRYING INTRODUCTION The wood veneer industry uses over a thou­ sand different wood species to make products as diversified as rotary-cut box shook YI inch (6.35 mm) thick to sliced decorative face veneer l,.loo inch (0.25 mm) thick. In the United States, the major veneer uses are for structural and industrial plywood components % to 1 inch (9.25 to 25.40 mm) thick and decorative ,vall panels and furniture parts %0 to 1 inch (4.76 to 25.40 mm) thick. With such a \vide array of raw materials and final end uses, the .field may at first seem overly complex. In part, this may be due to the scar­ city of written information summarizing the technical aspects of wood veneer manufacture. This bulletin describes the basic information known about the processes used in manufacture of wood veneer. Wherever possible, the log selection, log heating, veneer cutting, and dry­ ing processes are generalized and described as a continuum. To be sure, many individual proc­ essing problems are related to specific wood species. However, whenever possible the under­ lying cause is described and a generalized ap­ proach to the problem is suggested. Still, it is impossible to avoid some effects of individual species. In the past, when only a comparatively few species were used for veneer, this was not a great problem. It began to increase, however, as the favored species could not continue to meet increased demands J for veneer. Other U.S. species received closer hoks for this product, and species from other countries are being imported into the country in an increasing swell of species, qualities, and quantities. All of this has required more information­ information that has been pieced together painstakingly. Material on individual species is compiled for the benefit of the reader in the tables of the Appendix. But, whenever possible, the text of this bulletin tries to present the generalized approach, and for native U.S. species. Common names of wood species are generally given in this publication. But experienced users are well aware of the pitfalls of common names. Therefore, the corresponding official name of the tree from which the wood comes is shown in Appendix I, along with the specific botanical name. The information contained herein comes from Forest Products Laboratory publications, from other research ol'ganizations, and from contacts with the veneer and plywood industry. The bulletin is written primarily for people responsible for some part of the veneer manu­ facturing process. It may also be of interest to others, including those growing trees for use as veneer, for log buyers, users of veneer, and wood technology students. WOOD AND LOG CHARACTERISTICS AFFECTING VENEER PRODUCTION A successful veneer operation depends on three items: A supply of suitable logs, good processing techniques, and a good sales organi­ zation. Most important is an adequate supply of suitable logs. Then to produce suitable veneer, the logs must have the appropriate wood and log characteristics. The desired wood and log characteristics, in turn, depend on the end uses of the veneer. 1 VENEER QUALITY AS RELATED TO END USES In this bulletin, veneer is defined as wood cut ~'ioo to 14 inch (0.26 to 6.35 mm) in thick­ ness by a knife, whether by rotal'Y 01' slicing methods. Three characteristics of veneer that are desirable for all end uses are uniformity of thickness, minimum surface roughness, and minimum buckle. For decorative face veneer, control of figure, color, and depth of checks into the veneer are important. Other veneer containing natural defects, such as knots, knot­ holes, splits, and discoloration, can be used as inner plies in many products and as faces of some products like sheathing and container ply­ wood. Four broad categories and typical end uses of veneer are given in table 1, as well as some wood qualities as they relate to uses of veneer. The classification of species of veneer speci­ fied in Product Standard PS 1-74, Construction and Industrial PlY'wood, is listed in table 2. The classification is based primarily on the stiffness and strength of the species. Group 1 woods are the stiffest and strongest and group 5 the least stiff and strong. Properties thRt are considered include bending (modulus of elasticity and modulus of rupture). compression parallel and perpendicular to the grain, and shear. Classification of species of veneer specified in Product Standard PS 51-71 for Hardwood and Decorative Plywood is giyen in table 3. As indicated in the table, the classification is J.~ased on specific gravity. Face yen eel' for decorative plywood is graded primarily by appearance. Species for use in wirebound boxes as speci­ fied in Federal Specification PPP-B-585b are listed in table 4. The four groups are based on specific gravity and other properties of impor­ tance in containers such as strength as a beam, resistance to nail ,\'ithc1rawal, shock resistance, and tendency to split when nailed 01' stapled. An indication of the importance, for specific end uses, of all of the wood and log properties that are discussed in this paper is sho\"11 in table 5. HARDWOODS OR SOFTWOODS FOR VENEER The reasons for the better bending proper­ ties of hard,Yoods are not definitely known. T,yo possible explanations are that the hard,Yoods h::we less lignin than the softwoods, and that lignin in hardwoods is more thermoplastic than the lignin in softwoods. While construction and industrial plY'wood is generally made from softwoods, hardwoods are preferred for most other uses listed in table 1. Good bending properties are l)articularJy useful for some types of furniture. Most species can be successful1y cut into veneer. However, some are much easier to process than others. Hardwoods, as a class, are easier to cut into veneer than softwoods. This probably is because hardwoods can be bent more readily than softwoods (65).1 Al1 veneer bends severely as it passes over the knife that separates it from a bolt or flitch. Hardwoods, having better bending properties, bend with less damage as checks in the veneer than do softwoods. 1 Italicized numbers in parentheses refer to Litera­ ture Cited. 2 PHYSICAL PROPERTIES OF WOOD " Generally, the first information about a spe­ cies is obtained by a wood taxonomist or wood anatomist. Working with herbarium material and sman wood samples, he classifies the spe­ cies and describes its structure. This informa­ tion is valuable for screening species to be con­ sidered for use as veneer. Such information is often available from libraries or by contacting Federal and State wood research laboratories or wood technology departments of forestry schools throughout the world. Physical properties of wood of interest to potential veneer producers include specific grav­ ity, moisture content, permeability, shrinkage, extraneous cell contents, figure, odor, and cell size, type, and distribution. (Values for individ­ ual species are given in Appendix II, "Physi­ cal Properties of U.S. Woods for Veneer.") Specific Gravity Specific gravity or density is easily obtained and is often one of the first properties known about a species. As indicated in table 1, it can be used as a general guide in screening ·woods for use as veneer. For example, a wood ·with moderately low specific gravity is preferred for use as core and crossbands of decorative plywood. Detailed information is available about the variation in specific gravity of many species, and additional data are being collected for other species. Information on the specific gravity of wood species can prove commercially valuable. For one example, knowledge of specific gravity for the various pines proved important in founding the southern pine plywood industry. When this industry started, the question was asked if all species of southern pine could be used and still make a product that could be marketed in the same strength categol'Y as Douglas-fir for structUl'al softwood plywood. (Species are placed in various groups for use as structural plywood primarily on the basis of stiffness and strength; in general, the strength of wood is related to specific gravity.) Based on the }'ecorded strength values and specific gravity records, the ma,ior southern pines-loblolly, longleaf, shortleaf, and slash pine-were permitted to be marketed in the same category as West Coast Douglas-fir. The minor southern pines, which have lower specific gravities, did not meet these requirements. Thus, ·while not foolproof, specific gravity can be used to quickly SCl'een new species for ten­ tative classification. While most species can be cut into veneer by suitable manipulation of the cutting condi­ tions, it is mOl'e difficult to cut ·wood at the two extremes of the mnge of specific gravity. Very lightweight species tend to cut ·with a fuzzy surface. Dense species require more power to cut and tend to c1.evelop deep cracks in the veneer as it passes over the knjfe. Basswood, with a specific gravity (based on green volume and ovendry ·weight) of about 0.32, is toward the low end of the range for species that are successfully cut into veneer. Hickory, with about 0.65, is near the high end. Still, a valu­ able species like rose·wood, specifir. gravity of 0.75, can be successfully sliced into face veneer, but this requh'es suitable heating and limiting the cutting to thin veneer. In gluing, also, the denser the wood the more difficult it generally is to glue (62). Typical specific gravities of woods used for construction plywood are 0.41 to 0.55; for hard­ wood face veneer 0.43 to 0.65; for COl'e and crossband veneer of decorative panels from 0.32 to 0.45; and for container veneer from 0.36 to 0.65 (table 1). Obviously, there are exceptions to these general guidelines. For ex­ ample, butternut, with a specific gravity of 0.36, is a high-value face veneer. It is suitable for wall paneling but less suitable ·where hard­ ness is a factor, such as the top of a desk. Green Moisture Content Veneer is often cut from logs soon after the trees arc felled. Such bolts or flitches have essentially the moisture content found in the living tree. This moisture content in the ·wood has a distinct effect on cutting. In general, wood with a moisture content above fiber satu­ ration but not excessively high is best suited for cutting into veneer; this makes the wood more pliable than drier wood. In a number of studies we found that species ·with a natural uniform moisture c0ntent of about 50 to 60 percent cut well. 3 Table 1.-Veneer characteristics as related to end uses Broad end­ use cate­ gory ~ Construc­ tion and indus­ trial plywood PS 1-74' Face veneer for hardwood plywood and decora­ tive panels PS 51-71 1 Typical species Typical specific end use3 Building construc­ tion as sub­ floor, wall sheathing, roof sheath­ ing siding panels, over­ laid panels, concrete form Douglas­ fir, southern pine, western hemlock, white fir, western larch Prefinished decorative wall panels, furniture, faces of flush doors, kitchen cab­ inets and case goods, plywood block flooring Birch maple, sweet­ gum, tupelo, oak, lauan ·Walnut, pecan, cherry, African and Honduras mahogany, oak J How generally cut Rotary do. Flat sliced, quarter sliced, rift cut, half­ round Typical specific gravity range Typical veneer thickness Inch 0.41 to 0.55 1/12 to 1/4 .43 to .60 .45 to .65 1/28 to 1/6 1/50 to 1/24 Desirable veneer qualities Veneer characteristics permitted in faces Veneer characteristics permitted in inner or back plies High stiffness (MOE) and strength; moderate weight, readily glued A grade: 18 patches in C grade: Same as faces D grade: Tight knots, a 4- x 8- foot panel knotholes to 3-inch B grade: Sound, tight diameter, pitch knots to 1-inch dia­ pockets 2-1/2 meter, 1/32-inch inches across grain, split splits up to 1 inch C grade: Knots or wide, some white knotholes to 1-1/2­ pocket. D grade is inch diameter, splits not permitted in 3/8 inch by full Exterior type panels. panel length Attractive figure. Moderately hard, readily glued (Not applicable) Grade 1: A few small burls, pin knots, and inconspicuous small patches do. Grade 2: Discoloration, knots to 3/4-inch diameter, and burls to 1-inch diameter c- .. "- Core and cross­ band veneer for dec­ orative plywood PS 51-71 01 1 Container veneer and ply­ wood PS 1-74 1 PS 51-71 1 PPP-B­ 585b 2 Inner plies for products like pre finished wall panels, fUrniture, flush doors, and case goods Yellow­ poplar, basswood, cativo, lauan Rotary .32 to .45 1/20 to 1/6 Wirebound boxes, bushel baskets, paper-overlaid veneer, cleated panel boxes, plywood­ sheathed crates Sycamore, cotton­ wood, sweet­ gum, tupelo, elm, oak, hickory, Douglas­ fir, southern pine, hemlock, white fir, ponderosa pine Rotary and sliced .36 to .65 1/16 to 1/4 1 Product Standards. , Federal specification. Low weight, low shrinkage, straight grain, fine uniform grain, easily glued (Not applicable) Grades 1 and 2: As de­ scribed for hardwood face veneer Grade 3: Knotholes to I-inch diameter, splits 3/16 inch by one-half panel length Grade 4: Knots, knot­ holes to 3-inch dia­ meter, splits I-inch by one-fourth panel length, 1/2 inch by one-half panel length, 1/4 inch by full panel length, small areas of shake and doze High stiffness (MOE), Same as A, B, C, D for softwoods and 1, 2, 3, 4 high shock resist­ for hardwoods as described above. ance (MOR), high resistance to split­ ting (strength in tension perpendicular to the grain), light color, free from odor Some of the free water is forced out during cutting. This water apparently acts as a lubri­ cant between the wood and the knife and pres­ sure bar and aids the cutting process. The driest wood that we have cut sucr;ess­ fully into veneer at the Forest Products Laboratory was a flitch of teak with a moisture content of 25 percent. Like all teak, this flitch had a waxy extractive that probably aided the cutting. We tried cutting even drier wood, but were not successful. This came about because a man­ ufacturer wanted to slice air-dried planks of ponderosa pine into veneer lAo inch (1.50 mm) thick. The wood, which was at about 15 percent moisture content, was heated to about 200 0 F in water. Continuous sheets of veneer were pro­ duced from the flitches but the veneer had pro­ nounced checks on the side that was next to the knife during cutting. After cutting, the veneer sheets immediately curled into tight rolls like window shades, so they were unsatis­ factory. Because slicing of the wood at 15 percent moisture content was unsuccessful we took sapwood air-dried planks from the ~ame ship­ ment, and pressure-treated them with 'water to a moisture content of over 100 percent. Veneer lAo inch (1.59 mm) thick was then successfully sliced from these planks. In other words, when water is put back into relatively dry wood, the wood can be cut into veneer. Some species have a higher moisture content in one part of the tree than another. For example, the sapwood of Douglas-fir has ap­ proximately three times as much water as the heartwood. Butt logs of redwood often have much higher moisture content than upper logs. In addition to requiring long drying times, wood having a very high moisture content is more difficult to cut into veneer than wood of the same species but with a lower moisture content. Examples are some western hemlock (as high as 215 pct), redwood (as high as 245 pct) , and Douglas-fir (as high as 130 pct). In normal veneer cutting, the wood is com­ pressed just ahead of the knife. Wood with a very high moisture content can not compress until some water is forced out. As water is rela­ tively noncompressible, it is forced from the wood structure so fast that it ruptures the wood (fig. 1). Commercial experience indicates M 88966 Figure l.-"Shelling" or shattering of redwood veneer that was rotary-cut from a "sinker" log. The wood shattered because water was forced out of the wood too fast during cutting. that high moisture content in "sinker" logs of species like redwood makes them undesirable for veneer because of cutting and drying prob­ lems. Likewise, for a long time sapwood veneer of Douglas-fir was not considered A-grade; part of the difficulty was in cutting it into smooth veneer as easily as the heartwood, which has a lower moisture content. Wood may be damaged by freezing if it is stored in a cold climate. For instance, southern pine sapwood was damaged when logs were stored outdoors during the winter in Madison, Wis. Even worse damage was observed in a sweetgum log stored through a winter at Madi­ son when the temperature went from above freezing to as 10\-" as -20 0 F. The end of a bolt cut from this log is shown in figure 2. Ice was found in many of the cracks seen on this end section. Industry reports that walnut logs grown in California and shipped by rail to the East froze when crossing the Rocky Mountains. Veneer cut from those logs was nearly useless due to splits caused by freezing. Moisture content in the tree, then, is gener­ ally not a decisive factor in determining 6 Shrinkage A small degree of shrinkage is desirable for all wood that is to be cut into veneer. In gen­ eral, low shrinkage is related to lo,,;r specific gravity. The low shrinkage of teak and mahog­ any is one reason these are preferred 'woods for face veneer. However, even 'within species hav­ ing the same specific gravity, a considerable range of shrinkage exists. High shrinkage is undesirable because it: Puts more stress on plywood gluelines with changes in moisture content; may cause cracks in face veneer of crossbanded panels during service; and causes warping unless the cross­ banded panels are perfectly balanced. Radial shrinkage is generally less than tan­ gential shrinkage. Consequently, quarter-sliced veneer will often perform better as face veneer or cross band veneer than flat-sliced or rotary­ cut veneer of the same species. Longitudinal shrinkage may also be a factor in use of veneer. On several occasions we have seen thin decorative plywood panels bow seri­ ously because of the different longitudinal shrinkage characteristics of face and back veneer. Excessive longitudinal shrinkage may be due to short grain, to compression wood in softwoods, or tension wood in hardwoods. Shrinkage is a factor in all veneer uses but perhaps is most important for crossband veneer. Drying conditions may affect the total shrink­ age of refractory species like some eucalypts. J\f 84166 F Figure 2.-Splits and shake in this sweetgum log were caused by alternate freezing and thawing. whether wood is suitable for use as veneer. V\Tood with a very high moisture content is usually more difficult to process than 'wood having a moderate moisture content such as 50 to 60 percent. On the other hand, it is very difficult or impossible to cut good veneer from wood below the fiber saturation point, approxi­ mately 30 percent for all species. Permeability Permeability has a distinct effect on veneer cutting, drying, and gluing characteristics. Sap­ wood is often more permeable than heartwood of the same species. Bacterial attack in log storage may increase the permeability of wood, thereby changing its cutting characteristics. Wood that is permeable is easier to cut because water is readily forced from the 'wood; forces that could rupture the wood do not develop. Furthermore, plywood made from veneer that is natmally permeable, such as yellow-poplar, is less subject to "blowout" in the hot press than plywood made from such relatively imper­ vious veneer as spruce. Extremely permeable veneer, such as the sapwood of pine that has been attacked by bacteria, may require a heavy glue spread or changes in gluing techniques to obtain satisfactory bonds. W o,)d Structure and Growth Rate In general, it is desirable to have uniform wood structure for ease of cutting, drying, and processing of wood into veneer. The relatively uniform structure, regardless of growth rate, is one reason why diffuse porous hardwoods like yello'w-poplar, sweetgum, and yellovv birch are such goud veneer species. SimHarly, softwoods like white pine and Klinki pine are good veneer species. Uniform structure is particularly de­ sirable for crossbands of decorative panels to minimize "telegraphing" of the grain to the face. Such species as Douglas-fir, southern pine, and the oaks have a pronounced difference in density between springwood and summerwood. Assuming other factors are equal, veneer pro­ 7 ducers generally prefer slow-grown wood of such species. In practice this is not always pos­ sible; for example, most construction plywood is made from Douglas-fir and southern pine, much of it fast grown. However, veneer from slow-grown logs of these species cuts better, dries with less buckle, and is generally pre­ ferred by production personnel. For ease in cutting and drying, veneer logs of such species shOUld have a minimum of six rings per inch. Ponderosa pine growing in the Southeastern United States often has 30 rings or more per radial inch of growth. In tests at the Labora­ tory, we found this to be excellent wood for cutting into veneer. One of the problems that sometimes occurs with fast-grown softwoods is "shelling," a local separation of the annual rings at the spring­ wood-summerwood boundary (fig. 1). The first few layers of springwood cells are apparently weaker in resistance to shear than cells formed later in the year. Shelling may also occur with slow-grown wood that has soft, weak spring­ wood and high moisture content. Examples are western redcedar and redwood. Shelling is ag­ gravated by use of high compression by the nosebar and by excessive heating of the wood prior to cutting. Fast-grown wood of species such as Douglas­ fir and southern pine may cause problems in drying, gluing, and finishing (40). The same relationship holds for ring-porous hardwoods like oak. In such woods, it is desir­ able that the springwood portion of the annual ring be narrow and the summerwood be of moderate density. In other words, the desirable thing is to get as uniform wood structure as possible. Such oak wood cuts well, does not shell readily between rings, and performs well as furniture, paneling, or flooring. affect the appearance of the finished wood sur­ face. If desired, the filler can be used to accent the figure of the wood. Straight vs. Irregular Grain For ease of veneer processing and for most end uses, straight grain is desirable. Str.aight-grained wood is easier to cut than irregular grain and the veneer is more likely to remain flat. On the other hand, the market value of certain finished items of irregular grain may be high enough to pay for the extra care needed in handling it. Examples are the curly grain in species like walnut and maple and interlocked grain in mahogany. The curly grain often shows on a flat-cut or tang~ntial surface. Interlocked grain shows as a stripe on quarter-cut or radial surfaces. Identifying irregular grain in logs is discussed further under "Log Properties." Geneticists are studying the inheritance of interlocked grain in species like red gum. Such information would help in selecting straight­ grained trees to breed for lumber and veneer production. Parenchyma Parenchyma cells occur most frequently in wood rays and as concentric bands at the edge of growth rings. These cells are comparatively thin-walled and function primarily for storage of food. They are generally weaker than most other wood cells and so may form zones of weakness when they occur in large bands. Terminal bands of parenchyma in angelique make it difficult to rotary-cut that species with­ out getting a "shelling" type of failure at the bands of parenchyma. To a lesser extent this same problem occuned when rotary-cutting Veneer from Brazil nut (fig. 3). Parenchyma in wood rays may be trouble­ some when quarter-slicing veneer. The cut will be smooth when the knife moves across the wood in the direction in which the rays run out at the surface being cut. Conversely, ,,,hen the rays run out at the surface in the direction opposite to the movement of the knife, the cut is rough. In the first instance, the rays are com­ pressed by the cutting action and so cut smoothly. In the second case, the rays are stressed in tension perpendicular to the grain Texture Open-grained or coarse-textured woods such as oak and ash have large pores. This is rela­ tively unimportant in veneer cutting and dry­ ing but may be important in finishing. A furni­ ture wood with pores larger than those in birch must have the pores filled to get a continuous film of finish. Large pores also affect the ap­ pearance of the wood. The size of the pores and the color of the filler used to fill them will 8 solvents such as water, alcohol, acetone, ben­ zene, and ether. The range and mixture of extraneous com­ pounds found in wood is very large (28). Many of them have not been fully identified. Further, the amount of extractives varies widely from tree to tree and often within a tree. Therefore, only a few of the extraneous materials that may affect the use of wood as veneer will be discussed here. In general, the extractives constitute only a small percent of the dry weight of the wood. In exceptional cases, however, such as the resin in longleaf pine f;tumps, the total may be as high as 20 percent. Often the high concentra­ tion of extraneous materials that cause diffi­ culties in processing veneer results from a tree's response to injury. Heavy oleoresin con­ centrations are often found in southern pine trees that have been tapped for resin. Pitch pockets and blisters are generally considered to be caused by injury to the cambium of trees that secrete oleoresin. The wood contains pock­ ets of oleoresin, which flows readily when the defect is cut open. Fires are reported to stimu­ late gum production in several species. Insect attack is considered a principal cause of gum spots in black cherry. Wounding of hickories or pecans by cambium-boring insects often results in deposits of calcium carbonate or magnesium carbonate that are hard and large enough to nick a sharp knife. These examples suggest that the percentage of veneer logs free of objectionable concentra­ tions of extraneous materials can be increased in two ways: By selection of tree breeding stock that is resistant to insect attack, and by silvicultural practices that minimize injury to the trees. The terminology concerning extractives is sometimes confusing to nonspecialists in this field. This problem is complicated because most extracti ves consist of more than one compound. M 136 450 Figure 3.-Separation of a parenchyma band in rotary­ cut Brazil nut veneer. The scale is in inches. by the cutting action. As they are weak in ten­ sion, they split ahead of the knife into the wood and cause a rough surface. This phenomenon of differing roughness of the surface also applies to the orientation of annual rings and fibers (39) . Extraneous Cell Contents and Some Effects , Cellulose, hemicellulose, and lignin are the primary structural elements of the cell wall. Being polymeric in nature they are essentially insoluble in water and neutral organic solvents. Many other materials may also be present in the wood. They are not part of the wood structure, but they contribute to the wood such properties as color, odor, and resistance to decay. They are grouped under the general heading of extraneous resins, waxes, hard de­ posits, and the like. Gluing problems have some­ times been attributed to resinous and waxy deposits in the wood. Extraneous materials can generally be removed from the wood by neutral GUIU The word "gum" has been used in the past to describe any plant exudate that feels gummy when fresh and that hardens on exposure to air. In recent years chemists have used the word "gum" specifically for certain types of polysaccarides. True gum is more or less solu­ 9 ble in water and insoluble in nonpolar organic solvents. Arabinogalactan, which may be pres­ ent in amounts sufficient to interfere with the gluing of veneer cut from butt logs of western larch, is a true gum. Gum spots in black cherry probably consist of true gum anG polyphenols, with the polyphenols causing their dark br.-wn color. While a slight amount of gum is ,,1'­ mitted in cherry face veneer (7), moderate or heavy concentrations of gum 10'wer the grade. Figure 4 shows the gUl.l.l that limits use of Brazil nut for veneer. Resin and Oleoresin In contrast to gum, resin denotes materials that are hsoluble in water but soluble in neu­ tral organic solvents. Resins OCCllr in ray parenchyma cells of both hardwoods and soft­ woons. Oleoresin is a mixture of resin and essential oils; it is insoluble in \vater but solu­ ble in alcohol, alkalies, and most organic sol­ vents. Oleoresin is secreted by vertical and hor~ izontal resin canals in such softwood groups as pine, spruce, Douglas-fir, and tamarack. In hemlock, fir, andl'edwood, resin canals are nor­ mally absent but may be produced by injury to the tree. In veneer cutting, resin is a handicap. It may collect on the pressure bar and encourage chips to .i am between the pressure bar and the wood bolt, causing depressions in the veneer. Frozen or solidified resin in knots is very hard and will quickly blunt a sharp knife. Ether-soluble resin occurs in small amounts in many U.S. hardwoods, but genel'ally has little effect on their use for veneer. The relatively large amounts of ether-soluble components found in basswood may explain ,,-hy this species is more difficult to glue than would be expected from its specific gravity. Resin in core and crossply veneers, such as may occur in the heartwood of cativo and southern pine, is ob­ jectionable because it may bleed through the face veneer. Similarly resin in face veneer species like white pine can interfere with fur­ niture finishes. This is particularly true if the end product is a TV cabinet, which becomes warm during use. Among the imported hardwoods, vertical and horizontal resin canals are found only in cer­ tain species of Diptel'OCa1'pacear. The contents of these canals usually appear white 01' yellow. 7If 13G 441 Figure 4,-Gum in a sheet of rotary-cut Brazil nut veneer. These extractii'es may be part of the IJl'oblem in gluing kapur and kerning. Polypllen ois Polyphenols can be broadly grouped into tan­ !lillS and nOll tannins. :Mc.-.;t tannins are of a molecular size generally soluble in watel'. Poly­ phenols that are not soluble in water can be removed from wood with polar organic solvents like alcohol 01' aleohol-benzene. Polyphenols occur in most species and are generally more common in the heartwood than in the sapwood. Color One reason polyphenols are important is be-­ cause they give wood its typical color. Colored heartwood of decorative face veneel' of species like rosewood is much more valuable than Jip;ht­ colored sapwood. 10 • , Almost all sapwood is white. This light color is preferred for some face veneer of species like maple. Light-coloted wood may also be pref­ erable for containers as it makes a good back­ ground for stenciling or other markings. Color is of little importance for construction ply\\Tood or for core and crossband veneers. Hard Deposits The ash content of wood is usually less than 1 percent but in small areas in the wooel it can be much greater. The principal inorganic de­ posits contain calcium, magnesium, or silica. Concentrated minerals have a distinct blunting effect on sharp tools. However, scattered indi­ vidual crystals of calcium oxalate, which are common in the longitudinal parenchyma and ray cells (If many hardwoods, do not obviously affect veneer cutting. Hard deposits that do cause rapid dulling of knives are limited to a few native species such as maple, pecan, and hickory. The ash content in mineral streaks of hard maple is reported to average 5.2 percent and to be high in man­ ganese. Calcium deposits, concentrated in hick­ ory and pecan that is injured by cambium­ mining insects, will nick a sharp knife. In contrast to continental U.S. species, many tropical hardwoods contain silica. If the silica content exceeds 0.5 percent, it causes rapid blunting of cutting tools. Metal Stain Many polyphenols react with iroll and steel in the presence of water to form a blue-black stain. This becomes very obviou~ and obj ection­ able on face veneer of species like oak and red­ wood if the wet wood is in contact with iron or steel for even a brief time. Hot 'wet wood will stain more readily than cold wet wood. Dim02nsional Stability Nearn (49) showed that many heartwood extractives will partially stabilize the wood dimensionally. One result is that dry, rotary­ cut heartwood veneer of species like yellow­ poplar and Douglas-til' has less end wrinkling and buckle than sapwood veneer cut from the same logs. Flat veneer is easier to handle in plant processing than buckled or wavy veneer. Checks in Veneer Checks in the heartwood veneer of rotary­ cut types are measurably deeper than checks in the sapwood veneer cut under the same con­ ditions. Similarly, high-speed photographs have shown that breaks into the hem·twood veneer of yellow birch were more conspicuous than breaks into sapwood veneer cut in the same revolution of the bolt. One possible explanation of these phenomena is that the polyphenols in the heartwood make it less plastic than the sapwnod. • .. Wax A few species of wood have waxy extractives that seem to be an advantage when cutting veneer. Pencil manufacturers recognize tl- 'i,s advantage and add wax to incense-cedar pencil blanks to improve the whittling properties of the wood. Conversely, waxy extractives make wood more difficult to glue and finish. Examples of wood that feel waxy to the touch include teak, determa, and cypress. Figure Figure is defined as the pattern produced in a wood surface by annual growth rings, rays, knots, deviations from regular grain such as interlocked and wavy grain, and irregular coloration. Figure is one of the most important characteristics of decorative face veneer. How­ ever, for uses of veneer other than decorative face stock, highly figured wood is generally not desired. Odor Most woods have little odor when dry. Some species, such as cedars, have a pleasant odor that is used to promote the use of the wood. Other woods have a sour or unpleasant odor, particularly if they become damp. Logs stored in a warm climate may develop objectionable odors due to the action of bacteria. The prob­ lem is most likely to OCCllr with species that have "'ide bands of sapwood containing large deposits of starch. Such odors are particularly objectionable in veneer that is to be used for products like food containers or paneling for walls of homes. 11 MECHANICAL PROPERTIES OF WOOD Besides physical properties, the information most generally available about a species is its mechanical properties. rrhe most likely sources of information on mechanical properties of wood are libraries, Federal and State wood l'esearch laboratories, and wood technology de­ partments of forestry schools. Mechanical properties of particular interest for veneer are strength in tension perpendicu­ lar to the grain, hardness, modulus of elastic­ ity, modulus of rupture, shear, and compres­ sion parallel and perpendicular to the grain. (Values for individual woods are given in Appendix III, "Mechanical Properties of U.S. 'Voods for Veneer.") A wood strong in tension perpendicular to the grain is desirable for veneer because it is less likely to split in log form, when cutting into veneer, or in subsequent handling of the veneer. Hardness is of interest in veneer used for furniture and flooring, or other places where it will receive abrasion and impacts during service. Modulus of elasticity, or stiffness, is impor­ tant to veneer because stiffness of the plywood is generally the critical factor for such struc­ tural uses as subflooring and roofing. Modulus of rupture is a measure of the ulti­ mate bending strength of the wood. It is of interest for containers and for construction plywood. Shear is important in structural applications such as the use of plywood as the web in a box beam. 'When ply\\rood is used as a stressed skin, strength in compression parallel to the grain is important. Compression perpendicular to the grain is an important property when a bearing load is involved, such as a refrigerator on a plywood subfloor. Referring to end uses listed in table 1, con­ struction plywood is generally made from soft­ woods. A major reason is that, for a given specific gravity, softwoods generally h!ld thawing; development of undesir­ able odor; and increased porosity due to attack by bacteria. End drying and splits in logs can OCCur with susceptible species like dense hardwoods in one hot, dry, windy day when the sunlight falls cfu'ectly on the log end. End drying is less of a problem with a species like Douglas-fir stored in winter in the damp Northwest. Blue stain and mold can occur in a week to 10 days on the sapwood of species like sweetgum and southern pine stored in humid summer weather in the South. Decay generally requires weeks 01' months to develop. Oxidation stain, which low­ ers the value of white sapwood of species like birch and maple, may occur through the ends of unprotected logs stored several weeks during summer. Insects like lyctus beetles may attack a log w:thin hours after felling. To minimize insect attack, logs stored in warm weath('}' should be used within 2 weeks after felling, treated with an approved chemicaV or stored under water. Freezing and thawing of logs of species such as sweetgum and clal'o walnut may fracture the wood so that it is useless for veneer. This is less of a problem wi th species grown in north­ ern climates. a Check with the local County Agricultural Agent or State Agricultural Experinment Station for approved recommendations. 29 The sapwood of many species is subject to attack by anaerobic bacteria even though the wood is kept wet. This has caused objectionable odor, particularly in tropical hardwoods like muritinga, ceiba, and cativo. Bacteria may also cause excessive porosity in pines like ponderosa and the southern species. The best way to con­ trol bacterial action is processing felled h'ees within 1 month 01' by storing the wood below 40 0 F. (50 C). Spraying with chemicals may help, providing the bacteria has not already en­ tered the wood. Given these many possible pl'Oblems, what is the best procedure for log storage? In general, veneer log storage should be kept to a minimum. The first logs into storage should be the first ones out of storage for processing. r deal storage conditions would be to end coat and keep the bark intact on tree-length logs that are either held at high humidity and a temperature just above freezing (34 0 F or 1 0 C) 01' completely submerged in cold water (34 0 to 40 0 or 1 0 to 5° C). The next best system would be to keep the logs under a roof and all surfaces constantly wet by a water spray. This would be just as good as the first method, providing the tempera­ ture was between 34 0 and 40 0 F (10 to 50 C). A common storage method that is generally satisfactory is to keep all log surfaces wet with a water spray but without using a roof. When water spray is not feasible, then a chemical spray and end coating may permit satisfactory storage. Less desirable methods which are some­ times suitable include floating the logs in a pond and cold-clecking the logs. A much mOl'e complete discussion of log storage is given by Scheffel' (60). BARK REMOVAL The subject of bark removal is one in which two people, both knowledgeable in the field, may disagl·ee. The reason is the wide variability in difficulty of removing bark. Three factors that must be considered are: (1) variability of bark adhesion 'within a species; (2) variability of hark adhesion between species; and (3) type of equipment used for debarking. Variability Within a Giv("n Speci("s Spring-cut logs are easier to debark than fall­ cut logs of the same species. This general state­ ment is true for all species. Actual measure­ ments of the wood-to-bark bond on several species indicate that this increase of bond strength from spring to fall may be 100 to 200 percent. A second factor is the temperature of the wood and bark at the time of bark removal. Heated wood is much easier to debark. When veneer logs were commonly debarked by hand, a main reason for heating the logs was to make bark removal easier. Frozen logs are particu­ larly difficult to debark. A plant may even install a hot pond to get logs above freezing so they can be more readily debarked with a mechanical debarker. Another factor in debarking is whether or not the bark has been allowed to dry on the log. AssunJng no bacterial action has taken place, the bark generally adheres more tightly after it has partially dried. A fourth factor is the action of bacteria. Logs stored in a warm pond or under a sprinkler dUl'­ ing summer may be subject to attack by bac­ teria. Bacteria seem to prefer the inner bark as a food source. Consequently, Jogs stored in a ponel and attacked by bacteria may have the bark loosened so that it will come off in one big sheet. Such a big piece may jam the bark con­ veyor. Conversely, bacteria attack may make peeling of bark much ensier 'when using hand tools. Sj)eciel" Ditr (>r("11(~("S Individual wood species differ in strength of the bond between the bark and the wood. In one study of fall-cut logs, the bal'k-to-wood bond of quaking aspen was more than 40 percent stronger than that of red spruce. Some species like bass'wood and elm have stringy bark. This becomes a problem in con­ veying the material from a mechanical de­ barker, as bark may come off in 1alge sheets. In general, softwoods like pine are easier to debark than hardwoods like hickory, but there are many exceptions. For example, fall-cut east­ ern hemlock is reported to be more difficult to debark than northern hardwoods like maple and birch. Other examples of softwoods that are difficult to debark are cypress with a fluted base, 'western redcedar with stringy bark, and red­ wood with very thick bark. The difficulty of bark removal of species that grow in the United States is shown in Appendix IV. Types of Equipm("lll Used Different systems have been used for debark­ ing veneer logs, including hand tools, bark saws, "Yater under high pressure, flailing chains, and drum debarkers. Some mi11s have used an old lathe to debark and round bolts. At present, however, two methods are by far the most com­ mon for debarking veneer logs-the cambio­ shear or ring debarker, and the rosser-head debarker. Combination machines may use either cambio-shear or rosser-head or both. Some factors to consider in choosing a de­ barker, besides the original and operational costs, include species to be debarked, volume of wood to be debarked, maximum and minimum diameter of logs to be debarked, importance of fiber loss, pollution, ease of operation, and ease of maintenance. In general, the rosser-head debarker has a lower initial cost, lower maintenance cost, is easier to adjust, and is more adaptable for logs of a wide range of diameters. The rosser-head is generally preferred for debarking rough logs of species like hickory, logs that vary widely in diameter, and logs that may be frozen. The cambio-shear 01' ring debarkers are gen­ erally preferred by plants processing logs with relatively uniform diameters and where high production and low fiber loss are important. A typical installation would be in a large southern pine plywood plant. Several manufacturers of cambio-shear de­ barkers state that, by proper adjustment of tool pressure and feed, their equipment can debark any species uncleI' any conditions, including frozen logs. Similarly, manufacturers of rossel'­ head debarkers state their equipment can be used to debark any species under any conditions. 30 SAWING INTO HOI-,TS OR FI-,ITCHES ., It is generally desirable to harvest logs in as long lengths as possible and to saw into bolts or flitches at the veneer-cutting plant. The reasons for doing this include less waste from end dry­ ing of the logs, a better opportunity to observe all sides of the log before cutting, availability of skilled labor trained to buck and saw flitches from the logs for the best use, and better me­ chanical equipment for handling and sawing the logs. The sequences of debarldng, bucking into bolts, and heating depends on type of logs, de­ barking and sawing equipment at the plant, and whether log end splitting is a factor during heating. In general, debarking reduces heating time, as bark is a good insulator. Heating in long lengths reduces waste due to log end splits. On the other hand, bark indicators of hidden defects in the logs may help the sawyer decide where to break the logs for best grade. The bark may also protect the logs during handling. A method sometimes used with hardwoods that tend to end split is to debark in long log lengths, heat in long log lengths, and then buck into bolts just prior to cutting veneer. This method reduces the time required to heat the bolt by eliminating insulation by the bark. Log end splits are confined hU'gely to the ends of the long log and minimized at bolt ends exposed by crosscutting after heating. The process re­ quires a continuous debal'ker, long heating vats, and equipment to handle long logs. Other dis­ advantages are that the bark indicators of de­ fects are lost before bucking, and care must be used to prevent the debarked logs from picking up grit during handling. A method used with softwoods like southern pine is to debark in long log lengths, crosscut bolts, and then heat pdor to peeling. This re­ quires a continuous debarker but permits heat­ ing vats and handling equipment which work with 8-foot and shorter blocks. It is a satisfac­ tory method if end splitting is not a serious problem and the hanclUng equipment is kept clean so the debarked logs do not pick up grit. Large-diameter logs such as old-growth Douglas-fir are sometimes cut to bolt length in a pond, debarked in a machine designed for 8-foot lengths, and then heated 01' cut at room temperature. The debarking-sa wing-heating sequence used 31 for flitches is generally to buck to length, then saw the flitches, and finally heat the flitches. As flitches are generally a step in producing face veneer, bark indicators are important for cutting logs to length and for producing the flitches. Most or all of the bark is removed in sawing and so does not significantly retard heat­ ing. The heated flitches are cleaned and any re­ maining bark removed with a flitch planer just prior to slicing. Saws ('sed in Proeessill~ Lo~s to Bolts and .Flildws Logs are cut to length of bolts or flitches pri­ marily with large circular saws or with chain saws. In both cases it is important that the log and saw be positioned so the cut is at a right angle to the axis of the log. Logs m'e generally sawn into flitches with a bandsaw or a circular saw. The yertically mov­ able circular saw that is mounted over the log carriage permits sawing logs into thirds as well as halves and quarters. In all cases it is impor­ tant that the log can be accurately positioned with respect to the sawline and that the sawyer can see uoth ends of the log. If both lumber and \'enee1' flitC'hes are to be produced, the banc1­ saw mar be ad,'antag-eous, as generally a smaller saw kerf is produced. W'hat DOt'S 11i(' Sawyer' Look For? /Jolts Factors to be considered in bolts are sweep in the log, end trim, presence of large defects like knots, and the length of the bolts required. If possible, sweep in the log should be minimized as it results in excessive roundup and ShOlt grain in the veneer. Thus, even though long bolts are generally more valuable than short bolts, a log with excessive sweep would prob­ ably be more yaluable if cut into two 01' more bolts to minimize the sweej). Logs that have been end coated or that have dried and checked should be end trimmed. The cut should be at a right angle to the longitudinal axis of the bolt. Crosscutting with a hand-held saw can result in irregular bolt ends, which in tU1'l1 can reduce the surface engaged by the Jathe chucks and also cause the veneer to vary in length or re­ quire excess spurring at the Jathe. Flitches A log with s'weep should be sawn into flitches so the sweep is perpendicular to the plane of the knife used in slicing. This permits full­ length veneers from the start of slicing. A large split or frost crack in a log may be minimized by dividing a log along this longitudinal plane. If possible, knots or other defects indicated in the bark should be trimmed out or be put at one edge or end of the flitch so the defect will occur at the edge or end of the veneer. In general, it is desirable to saw the flitch parallel to the bark and take the taper from the center of the log. This makes fOl' straighter grain and a balanced design in the face veneer. The side of the flitch that is to be the exit side for the knife at the end of the cut should be sloped, with the wide side next to the flitch table to minimize tear-off during slicing. The top and bottom of the back of the flitch should be squared so the slicer dogs can obtain a good grip. The recent develop­ ments of remotely controlled extension dogs and a fixture for holding the flitch by vacuum make this precaution less important. Frequently the smyyer preparing flitches for face veneer has the option of sa'wing the log for lumber. This judgment is generally made after he has sawn through the pith and can see the quality and figure in the wood. If the log has some limitation for slicing, such as ring shake, it may still be possible to recover high-quality lumber. Choice of Cutting Direction Some of the ways bolts or flitches are pre­ pared and cut into veneer on a lathe or a slicer are illustrated in figure 11. There are two main directions in which veneer can be cut-parallel to the annual rings (rotary-cut) or parallel to the wood rays (quar­ ter sliced). The other methods fall between these two extremes. Half-round , flat-slicing ' and back-cutting all result in cutting parallel to the rings in the center of the veneer and at angles to the rings at the two edges of the veneer sheets. Rift-slicing is a deliberate attempt to cut midway between parallel to the rays and perpendicular to them. The lathe is used to cut practically all veneer used in construction plY'wood, some decorative face veneer, and most container, core, and cross­ band veneer. Slicing and stay-log cutting is done primarily to produce decorative face veneer. A stay-log is an attachment for a veneer lathe on which flitches may be mounted for cutting into half-round, back-cut, or rift veneer. Very high­ quality core and crossband veneer is occasionally produced by quarter-slicing. Small, fast slicers have been used to produce container veneer. Rotary Eighty to 90 percent of all veneer is cut by the rotary method (fig. ll-A). The rotary method gives the maximum yield; it results in the widest sheets; knots are cut to show the smallest cross-section; and most juvenile wood and splits are left in the core. Some rotary-cut veneer is used for the decorative effect of an­ nual rings or irregular grain, such as that causing "blister" figure. Flat-Slicing and Half-Round Cu.tting Flat slicing (fig. ll-F) is done on a slicer, and half-round cutting (fig, ll-B, C) is done on a lathe. Half-l'olllld cutting may be done with flitches mounted on a stay-log (fig. ll-C) , or by chucking a bolt at one edge rather than at the center, and by having the lathe chucks mounted eccentrically (fig. 11-B). Veneers produced by the flat-slicing and by half-round cutting are similar in appearance. The centers of the sheets are essentially flat-grain 'while the edges are rift or even quartered material. The half-round method gives slightly wider sheets and a bigger area of flat cutting in the center of the sheet than the flat-slicing method. These two cutting methods show growth rings to advantage. When the grain dips in and out of the sheet, the figure is broadly termed "crossfire." Burls are gen­ eral1y cut by the half-round method and crotches by the flat-sliced method. Rift-Cut A quarter section of a log is cut and mounted so that the knife cuts about a 45° angle to the 'wood rays. This can be done with a stay-log on a lathe (fig. ll-E) or on the slicer (fig. ll-H). The method is used primarily with white oak to produce a figure caused by the 'wood rays. When the veneer is coarse-textured and the annual rings are not exactly parallel to the edge of the veneer, the figure is called rift-cut. A form of rift-cut that is particularly desirable is comb 32 • LATHE SLICER A. ROTARY (YELLOW BIRCH) F. FLAT SLICED (WALNUT) B. ONE-HALF ROUND (RED OAK) G. OUARTER SLICED (PRIMAVERA) C. ONE-HALF ROUND (BLACK CHERRY) H. RIFT SLICED (WHITE OAK) D. BACK CUT (ROSEWOOD) I. WHOLE LOG (FLAT SLICED) (ASPEN) E. J. RIFT CUT (WHITE OAK) I. FLAT SLICED 2. BACK CUT 3. OUARTER SLICED M l40 660 Figure ll.-Some of the cutting directions used to obtain different grain patt{'rnf; in veneer. The species in paren­ theses are typical of those cut by the method diagramed. The wide dark lines under "slicer" represent the back­ board left at the end of slicing. 33 grain. By contrast "with the more familiar form, comb grain has fine texture, straight grain, and no broad flakes. Quarter-Sliced Quarter-slicing (fig. ll-G) produces straight, narro,,' stripes in straight-grained softwoods like Douglas-fir, redwood, and western red cedar or straight-grained hardwoods like oak and wal­ nut. Quarter-slicing is also done with species haying interlocked grain such as mahogany and primavera. This produces a plain stripe or ribbon-grain which reflects light in different directions depending upon the position of the yiewer. Plain-stripe is a comparatively broad stripe and not too pronounced. A ribbon stripe has narrower bands and is more highly reflec­ tiYe. When the grain in the wood dips in and out of the sheet, the figure is calleel a broken stripe. Back-Cut Back-cutting (fig. ll-D) is done on a lathe with a stay-log, much like half-round cutting, Howeyer, instead of cutting from the sapwood side, the cut is from pith side of the flitch. B~lck-cutting is uncommon and is done where the heartwood is narrow and much more valu­ able than the sapwood. Rosewood is an example of this. Sau'n At one time sawing was a common method of producing veneer, but it is almost obsolete be­ cause of the large yolume of material lost as sU"wdust. Sawing does have the adYantage that it is not necessary to heat the log or flitch 11rior to cutting, the two sides of the yeneer are essen­ tially the same in quality, and thicker yeneers can be produced without developing cracks into the Yeneer. An example where these adyantages are important would be the top or back of a musical instrument, such as the guitar. Species like spruce, oak, cypress, and eastern red cedar are occasionally sawn. Sawn material can be flat-cut, quarter-cut, or rift-cut much the same as when slicing "dth a knife. Figure ," J-elleer As briefly described under the different cut­ ting directions, the appearance of veneer can be greatly affected by whether the veneer is C'..it tangential to the allnual rings, at tl right angle to the annual rings, or somewhere in between. T'igures 12 to 15 are examples of the appear­ ance of face veneer. CONDITIONING "WOOD PJUOU TO CUTTING VENEEH The moisture content, permeability, and the temperature of wood can have a marked effect on veneer cutting. Wood .l\1oiSlUl'(' Content POOl' cutting results if nearly all cen cavities in the 'wood are lilled with water or if the mois­ ture content is below the fiber saturation pohlt (about 30 percent for all species). Unfortu­ nately, there is little the plant manager can do to drastically change the moisture content in a bolt or flitch. Rapid processing, storage under water, or a sprinkler system will prevent green logs from drying. Logs having very high mois­ ture content cannot be partially dried quickly without developing degrade at the outer por­ tions of the log. Steaming may slightly reduce the time required to fu'y the veneer. \Vood Pf'I'JJ1eahiJiI.y The more permeable wood is to water, the easier it is to cut. But permeability is also largely inherent in the species. Sapwood of some species can be made more permeable by storing ill a 'warm, wet condition so bacteria will attack it. This may make it easier to cut into veneer but it may also affect the odor of the wood and its gluing properties. These disadvan­ tages make it unlikely industry will purposely induce bacterial attack to improve cutting. ~Tood T(,Ul]Wl'atur-e The major factor under control of the plant manager is the temperature of the wood when it is cut. This is an area ,,,here strong' differ­ ences of opinion exist among veneer plant man­ agers. For example, a hardwood plant manager 31 ',; ; \1 , ;c· .,\.; \1 I::~l 11 t'"' Y..!:"\\" l,ir.·h \lith tIll' liIWl'" f·:l1;~.'d 11): aut: ('ost and he dic1110t want log hpat­ illg eCluipmellt ill a plant that \,'as to be huilt. Defore ('ommenting on these statements, let's exami]]e SOUl(' of the known effects of' heating on gn'en wood. Jtll!al'\--('ut Figll!'(' SOIl/(' 1~/J('('I,o; of Healillg 011 (;1'(,(,11 JT'()od PJa,;li('it} lIt'atillg g'l'een "'f)()d makes it mOl'e 111astic. 1'11 is fad is pasiJ~' del!l!l11::;trated with mechan­ jut! tl':4;-; and i;-; tIw ba::;is of steam bending of Wood. Within thl' limit::; lISPc] ill \'e1](>('1' produc­ tioll, pJa:--:Ueity is not time-depemlent; as 80011 'I ;::'.' Fig-un. 11. un' i~ (':tl1Sl l~ift-"Ilt'(>c1 whit!' oak. TIll' d h~ ('uttl!!:':: till' al"I\.I\ \', Illd ray' :01',' t"'llI'i] .,!rq" :l!. a~! at~l.-·lt· :'I! "I' l~, , as green wood read}(>s it gi\'en iempt'ralul'E', it i:-; a;; plastic a:-; it ,dll gel ;It that temppratu]'('. VL'lll'el' ('ut fl'()lll IlP:ltp<1 IHljf:-; Ill' llitehe:-; ('all ],,, bent with fewer j'r;wtuJ't':, than \'PI1('PI' ('U1 from llllheatpd wood, This errpd is nlOl'e llo1i('eal>le with dense sjll'dp,:; and when ('uttillg thkk \'L'IlPel'. 1f a plant i;; intere;,;ted ill cutting tight. thiek veneer from dell~e ;;pe('it':'. then hNlting of the holts 01' ilitc:he::l i.. all imllort;wt part of the process, \1 : <:'1 ;' t ~ F:g-up· 1~\ (2:iart~'l'-;-1:t'!'d pr;!naY(l'*a. Thp hrlll-:;t'll . .:tdpp j.,e:'~r" j,: f'a ~ ... , d i!~\ ,~,,-!,' I\'J~~·d ~r;liq wl;i,'h dif'~ tli a!.tl .• :~: .. 1' :t:IL "I,I'l't. IranirH',.... 11 eat i Il~~ \\'l't \\-()od lll:tl\!'~ it ;;ofter, Hard knot:" \\'hil'll it' llltllPatl'd lJl:l~' !lick a :,harp kllif,', will nfb'Jl lIP :'I,f'telll,d ),y I!palillg' ::;0 the~' (';111 be ('ut. I1eat al:-" ~oft(,JI~ JlIkL but doe;; not ,:ofteIl milleral dl'l 'IJ"it" like ('aki\ll11 (':u'bollate alld "ijit':l, \YhilP heatillg' gl'lItor;tll~' aid,; ('uti illg' of dellse ;;pl'cil'':, it may (I\'er,:oflt'll ]..,:< dl'll::;p :'jlPl'ies and I'l':,ult III t{'alitl~~ ,,1' till! J ' \ U I BOLT \ 0 ~=--., \ \ <:;::1 I I r! Ii ,<',> ...... ...... _I~ (,?,/ ./ - KNIFE ANGLE KNIFE 1>1 140 Figure 17.-Cross section of a veneer lathe hadng a. fixed pressure bar. 46 fir., KNIFE ANGLE OFFSET- MHO 656 Figure lB.-Cross section of a vertically operating veneer slicer. The pressure bar on both the lathe and slicer compresses the wood, with maximum compres­ sion ideally occurring just ahead of the knife edge. This compression reduces splitting of the wood ahead of the knife, reduces breaks into the veneer from the knife side, and forces the knife bar assembly against the feed mechanism, thereby helping control veneer thickness. For both the lathe and slicer, the pressure bar is, therefore, important in controlling the rough­ ness, depth of checks, and thickness of the veneer. The slicer has a fixed nosebar while the lathe may have a fixed nosebar or a rotating roller bar. Advantages of Lathe Logs to be cut into veneer on a lathe need to be crosscut to the desired bolt length, but they do not need to be processed through a sawmill prior to cutting veneer. After roundup of the bolt, the Jathe cuts a continuous strip of veneer. Continuous cutting is advantageous because it means more production with a given cutting velocity, wider sheets of veneer, and a more uniform cutting condition. Full rotary ('utting is approximately tangential to the annual rings and knots are exposed at their smallest cross section. In full rotary cutting, there is no im­ pact at the start of cutting or tearoff at the end of cutting as may occur when slicing or cutting with a stay-log. Advantages of Sli-cer A main advantage of the slicer is that it per­ mits sawing the log into flitches to present the most decorative grain pattern. As the veneer sheets are kept in consecutive order, figured veneer can be readily matched. Flitches can be heated with less danger of end splits developing than in comparable bolts being heated for ro­ tary cutting. Sliced veneer is always cut from a flat surface, and most veneer is llsed on a flat 47 F KNIFE AND FIXED BAR KNIFE AND ROLLER BAR M 144 168 Figure 19.-Knife and pressure-bar terminology. Symbol A B C D E F G H I J K Alternate Term Preferred Term Knife angle Knife bevel angle Clearance angle Lead Pressure bar bevel Gap Exit gap Nosebar compression angle Knife surface next to wood work piece ** Knife surface next to wood ,reneer ** Length of knife bevel Knife pitch Knife sharpness angle Verticalopening * Pressure bar sharpness angle Horizontal opening * Restraint Bar angle * Satisfactory for verticaily operating lathe or slicer but is misleading for horizontally operating slicers. *'" The term knife face is sometimes applied to J by knife manufacturers and to I by lathe operators. To reduce ambiguity, this terminology is suggested. 48 surface. By contrast, rotary veneer cut from a curved surface must be flattened for most uses. The disadvantage of cutting from a curved sur­ face becomes more pronounced with thicker veneers cut from small-diameter bolts. Sliced veneer is cut with a draw motion across the knife, while rotary veneer is cut with no draw motion. Theoretically, the draw cut should aid cutting. However, recent experi­ ments at the U.S. Forest Products Laboratory indicate that the effect of the draw cut on smoothness, tightness, and veneer thickness is relatively unimportant. Veneer as long as 16 feet is produced on a slicer while most rotary-cut veneer is 10 feet or shorter. The flitch on a slicer is backed by the flitch table while support for a veneer bolt may be provided by a baC'kup roll. Adt·antages of Cutting with Stay-Log on Lathes The stay-log makes it possible to produce veneer on a lathe, similar in appearance to sliced face veneer (fig. ll-C). The advantages of stay-log cutting on the lathe are very similar to the advantages of slicing. The flitches can be selected for appearance of the grain and consec­ utive sheets can be matched for decorative faces. Sheets cut with the stay-log are generally wider than sheets cut on the slicer. For ex­ ample, half-round veneer cut with a stay-log would probably be sJjghtly wider than flat-sliced veneer cut from the same log. Veneer cut with a stay-log is taken from a curved surface in comparison with veneer that iR slked from a flat surface. Veneer cut wHh stay-log may be up to 10 feet in length. Back·Roli Lathe A modification of the rotary lathe is the back-roll lathe (fig. 20). It cuts the veneer rib­ bon to preset widths and so replaces a clipping operation. This special type of lathe has "'lays that carry the knife-bar head-blocks extended out on the log side of the lathe. On the extencled ways, a frame is mounted to carry the back-roll. The entire mounting is fed toward the log by feed screws at the same rate at which the knife is fed. Knives mounted radially in the back-roB make an impl·ession into the veneer bolt slightly deeper than the thickness of the veneer being cut. Then as the veneer is cut, it separateR into pieces the same width as the spacing of the knives on the back-roll. Since the scoring knives cut slightly deeper than the veneer thickness, they generally leave a light score mark on the tight side of the next piece of veneer. The back-roB lathe is, there­ fore, better suited for cutting thick container veneer than thin decorative veneer. All lathes are generally equipped with spur knives so veneer can be cut to one or more lengths while it is being peeled. Some General Comparisons of Veneer Cut on the Lathe and Slicer In general, the greatest yield if' obtained by rotary cutting. Half-round, flat-slicing, or back cutting provide intermediate yields; and the least yield is obtained by quarter- or rift-slicing. The smoothest and tightest veneer can be produced by quarter- or rift-slicing, followed by rotary cutting; the roughest and loosest veneer is produced by flat slicing, half-round, or back­ cutting. Differences in roughness are due to the effect of wood structure orientation (39). While slicing and rotary cutting involve some differences and inherent advantages, good-qual­ ity veneer can generally be produced by either method. The quality of the end product is de­ termined more by the log quality, the heating of the bolts or flitches, and the setting of the knife and pressure bar than by differences in the cutting method. Undesirahle Movement of Wood and Machine Parts Knife and pressure bar settings are meaning­ ful only if the wood is held securely in the lathe or slicer and if the machine parts have a mini­ mum of play. Undesirable Movement of JfIood on Lathe Bolts are held by chucks in a lathe. In gen­ eral, the larger the chucks the more securely the bolt is held. The chucks transmit the torque needed to cut the veneer and also must resist the tendency of the bolts to ride up on the knife. The spurs on the chucks should, therefore, be designed not only to transmit power to turn the bolt but also to keep it from shifting from the ~pinclle center. The best spur configuration is not well established. Some mills prefer half 49 WOOD BOLT BACK ROLL + SCORING/ KNIVES M 14' 658 Figure 20.-B~ck-roll circles; others, star-shaped spurs and a ring around the circumference of the chuck. In prac­ tice, the spurs sometimes become battered and bent and may collect wood debris. For best per­ formance, they should be in their original shape and clean. The chucks and spindle ends should be tapered for a positive secure fit. The pressure used to set the chucks in the bolt ends depends on the wood species, heating, and ch uck size. Generally, enough pressure is used to indent the spurs at least three-fourths their length into the bolt ends. Square-cut bolt ends allow a more uniform grip than bolts that are end trimmed on a bias. The wood in contact with the spurs receives fluctuating loads during cutting, which may cause the bolt to become loose in the chucks. On older lathes, the operator must watch for this and further indent the spurs if any loose­ ness of the bolt is observed. Newer lathes have hydraulic chucking. A relatively high pressure is used to set the chucks and then a lower pressure is maintained hydraulically to insure the spurs remain seated during cutting. If too lathe. high hydraulic end pressure is used during cut­ ting, the wood bolt may bend when it reaches a small diameter. Another modern solution to holding the bolts more securely is the use of retractable chucks. Larger chucks and spindles hold the bolt at the start of peeling; they are retracted during peel­ ing, allowing smaller inner chucks and spindles to hold and drive the bolt until the final core diameter is reached. A modificatioll of this is sequentially retractable chucks such as 5-inch (13 cm) inner chucks, with one 8-inch (20 cm) outer chuck on one end and one 12-inch (30 cm) outer chuck at the other end. The bolt is first driven with the 12-and 8-inch chucks. At a bolt diameter of about 14 inches (35 cm), the 12­ inch chuck is withdrawn and the bolt is then driven with one 8- and one f-inch chuck. At a diameter of about 10 inches (25 cm), the 8­ inch chuck is withdrawn. Cutting is continued with the two 5-inch chucks driving the bolt to the final core diameter. To obtain maximum recovery, bolts are turned to as small a diameter as practical. The 50 bolt is loaded as a beam by the knife and pres­ sure bar. Its resistance to bending is directly related to the cube of the radius of the bolt. At small bolt diameters, an unsupported bolt bends in the middle away from the knife. The bolt becomes barrel-shaped and the veneer rib­ bon wrinkles in the middle. To overcome this problem, backup rolls have been built to support the bolt during cutting. Some early backup rolls operated with a fixed pressure against the bolt. But this caused problems. The cutting force fluctuates during peeling, and a fixed pressure against the bolt surface sometimes increased rather than re­ duced bowing of the bolt. Improved backup rolls fix their position geo­ metrically to keep the bolt cylindrical. One method of doing this is a servo-system with a follower at the end of the block that signals adjustments of pressure on the backup roll. Another method (22) is to have this backup roll positioned mechanically by the feed mecha­ nism so the bolt remains a cylinder. When properly made and operated, backup rolls permit cutting bolts 8 feet long (2.44 m) to a final core diameter of about 4 inches (10 cm). Undesirable Movement or Play in Lathe Machine Parts G The wear problem with feed screws is greatly reduced by a ball feed screw drive. Motion of the carriage for the pressure bar and knife is obtained by ball bearings turning a ball screw. This movement by rolling friction means less wear than for sliding friction with an acme screw and nut. Most production lathes develop some play between the knife frame and the bar frame. The amount of movement depends on the loose­ ness in the lathe and the amount of pressure exerted against the bar during cutting. To de­ tect and correct for this play, dial gages should be mounted at each end of the lathe with the gage on the knife frame and the sensing tip against a bracket on the bar frame. These gages should be zeroed after setting the gap or hori­ zontal opening. Any play will show on the gages as a reading other than zero and the original gap or horizontal opening restored by adjusting the nosebar until the gages read zero. Wa.lser (67) describes a method to preload the pressure bar assembly to improve accuracy when setting the veneer lathe. Play can also affect the lead or vertical open­ ing. This is less common than play in the gap or horizontal opening. Again, dial gages can be mounted to detect and guide correction of the play. Spindle Overhang All movable parts must have some cleal"ance, and wear increases this clearance. Many lathes have built-in methods of taking up slack as wear progresses. However, it is not uncommon to find that production lathes have developed excessive wear and looseness or play in the mechanism. Some specific areas to check are spindle sleeves and bearings, feed screws, head­ block or knife-.:mgle trunnions, nosebar eccen­ tric, and blocks under SCl"ewS used to change the lead (vertical adjustment) of the pressure bar. The greab;~- wear is likely to be in the spindle sleeves and bearing, with the next largest amount in the feed screws and movable parts of the nosebar assembly. Some modern lathes minimize these problems by using pre­ loaded roller bearings for the spindles and an air cylinder to keep the knife bar always against one side of the feed screw. In addition, some lathes have replacable wear surfaces for the ways. Other things being equal, the greater the overhang of the spindles the more spring in the cutting system. This is most noticeable when short bolts are cut on a long lathe. If both short and long bolts are to be cut on the same lathe, the lathe should be equipped with spindle steady rests. Heat Distortion of Lathe Bolts that have been heat-conditioned prior to cutting may cause the knife and pressure bar to distort. It is generally agreed that heat­ ing causes the knife to rise in the middle, de­ creasing the lead. Heat may cause the preSSUl"e bar to drop or move in a horizontal plane, de­ pending on the lathe. On some lathes, one method of correcting for these changes is to adjust the pull screws on the A-frame built over the pressure bars for this purpose. A bet­ ter solution is to heat the knife and pressure bar to the expected operating condition prior to 51 the final fitting (setting) of the knife and bar. Some lathes have had heating elements built in them to prevent heat distortion. Another good practice is to store sharpened knives in a warm area so they are at the same temperature they attain during cutting. Feihl and Godin (14) suggest heat distortion can also be controlled by continuous cooling of the knife bed and the pressure bar bed. However, they and others indicate heating the knife and bar works better than cooling, particularly for long lathes. Undesirable Movement of Wood on Slicer The wood flitch is generally held against the bed on a vertical or horizontal slicer with dogs. In some vertical and all horizontal slicers, grav­ ity helps hold the back of the flitch against the flitch bed. However, in the most common ver­ tically opel"ating face veneer slicers, the flitch is cantilevered from the bed and dogging is very important. Heated flitches may be bowed or twisted. Very often this bow or twist can be removed by forcing the flitch flat against the flitch table and dogging it securely. Here oversized dogs are useful at the start of the cutting. A recent development has been retractable dogs, which are extended for maximum holding power at the start of slicing and then automatically re­ tracted when the slicing cut approaches the dogs. Older slicers had the dogs set by screws. After intermittent cutting, the flitch would often become loose, so the slicer would have to be stopped and the dogs reset in the wood. Modern slicers have hydraulic dogs which maintain good contact with the flitch through­ out cutting. The hydraulic cylinders actuating the dogs have check valves to prevent the flitch from shifting during slicing. A recent practice is to glue vab:tble flitches such as walnut to an inexpensive backboard and then slice to the glueline. Special glues and gluing techniques are used to bond the hot wet flitches to the backboards. Another innovation is to hold the flitch against the table with a pattern of vacuum cups. The flitch back should be wide, smooth, and flat or the flitch may break loose from the table during cutting. Undesirable Movement or Play in Slicer Purts Play can develop in all moving parts such as feed screws, offset mechanism, flitch table ways, nnd knife-bar carriage ways. Most mod­ ern slicers have means of taking up slack in these parts. A regular maintenance schedule should be followed. F eell hy Pawl and Ratchet Some slicers advance the knife by a pawl and ratchet for each stroke. This is highly accurate providing the same number of teeth are ad­ vanced each stroke, there is little play in the feed mechanism, and there is no overtravel of the carriage. The number of teeth advanced each stroke should be checked several times be­ fore and during actual cutting. The brake on the shaft which advanced the knife each stroke should be adjusted so there is no o'lertravel. Feed to a Stop Plate Some slicers feed by moving the previously cut surface against a stop plate. The surface of the flitch and of the stop plate must be free of splinters or other debris and the flitch must be advanced flush to the stop to produce veneer of uniform thickness. Offset on Vertical Face Veneer Slicers The offset mechanism on modern slicers is hydraulically operated and does not generally require attention once the cam is set to retract the knife at the bottom of the stroke. The amount of offset is adjustable and should be large enough to insure clearance of the flitch on the upstroke. Excess offset should not be used as it may induce slight vibration to the knife. The knife and bar carriage pivot on half bearings for the offset. Since the half bearings are not held at the top, if the flitch fails to clear on the upstroke, the knife bar carriage may be lifted from the half bearings. Similarly, high nosebar pressure cannot be used without danger of unwanted movement of the knife carriage on the half bearings. As with the lathe, it is desirable to have dial gages mounted at each end of the slicer with the gage on the knife frame and the sensing tip against a bracket on the bar frame. The gages are particularly useful for returning to the 52 previous setting after the bar has been re­ tracted to hone the knife. Heat Distortion of Slicer Since face veneer slicers are generally longer than lathes, heat distortion of the knife and bar may be more of a problem. As on the lathe, the heated knife rises in the middle and the pressure bar drops. The pull screws on the A-frame on the casting holding the bar can compensate for movement due to heat. A better solution, and one that is built into modern slicers, is a means of heating the knife and bar prior to fitting them, and then keeping these parts continually warm. This not only greatlY reduces any changes in the knife-bar setting due to cutting hot flitches, but also reduces con­ densate and the iron-tannate stain that results when iron or steel particles come in contact with wet wood. Dynamic Equilibrium on Lathe and Slicer Many have observed that the first sheets from a flitch on the slicer and the first few revolutions of veneer from a bolt on the lathe are thinner than the nominal knife feed. Hoad­ ley (29) studied this phenomenon with a knife and pressure bar mounted on a pendulum dyna­ mometer. He attributed the thin first cuts pri­ marily to compression of the wood beyond the thickness of cut, followed by springback after the cut. With the same advance, both the com­ pression and springback became progressively larger until a full thickness chip was produced. Hoadley called this dynamic equilibrium. Later studies on both an experimental and commercial lathe at the Forest Products Labor­ atory (44) indicated that the thin cuts were due mainly to takeup of slackness in the lathe. Veneer cut from a small, more rigid experi­ mental lathe reached full thickness quicker than veneer cut on a 4-foot-long commercial lathe. When the pressure bar was against the wood, it tended to force the bolt and knife in opposite directions. When the bar was re­ tracted and the knife alone engaged the bolt. the knife and bolt were drawn together. As a result, opening the bar (for example, to clear a splinter) dE ring cutting results in large changes of veneer thickness on a lathe that has slack­ ness. In contrast, if the pressure bar is kept closed from the start of cutting, then much of the slackness in the lathe will be taken out by the time the veneer is wide enough to use. This veneer will be more uniform in thickness than veneer cut just after the pressure bar has been closed. Some slicer operators set to cut tight veneer and run into a gradual buildup of the flitch face with respect to the knife due to cutting veneer thinner than the feed. Eventually, the knife carriage will vibrate due to excessive pressure against the knife and pressure bar. The operator will then thl'OW off the feed for one stroke, cutting a thick shim and continue to cut. This is poor practice as consecutive sheets cut after each shim are gradually chang­ ing in thickness. Better practice is to change the pressure bar setting (larger lead Or gap) so that a constant full thickness veneer will be cut. Effect of Speed of Cutting on Veneer Quality "Vhen Knospe (33) reviewed some of the veneer cutting literature in 1964, he concluded that cutting speed has a mIl imal influence on the quality of veneer. Recent unpublished work by A. O. Feihl indicates that for practical pur­ poses this is true within the speeds of about 100 to 500 feet (30 to 150 rn) per minute. However, at least two studies (6,1;1]) h&ve shown that the strength of the veneer in ten­ sion perpendicular to the grain decreases with an increase in cutting speed. Lower strength in tension perpendicular to the grain is generally caused by deeper checks into the veneer. In addition, high cutting speed with wood species having a very high moisture content may in­ crease the incidence of mashed grain and shell­ ing. In summary then, the cutting speed does not seem to be a critical controlling factor for most veneer production. However, if optimum veneer tightness and smoothness are important. it may pay to use a moderately slow cutting speed. When slicing l:i<-inch and thicker veneer, there may be a slight vibration of the slicer due to the impact at the start of the cut. Inclining the length of the flitch 3 0 to 50 from the long direction of the knife lessens this impact as the cutting starts at one corner of the flitch. A slower speed also reduces the impact at the start of each cut. 53 KNIFE AND PRESSURE BAR ON LATHE AND SLICER Type of Knife Selecting the Knife JVIost veneer knives are supplied the full length of the lathe 01' slicer. However, two- and three-piece knives are sometimes used with a special clamping arrangement so they can be ground and set as a unit. If one section is damaged, it can be replaced without replacing the entire knife. The hardness of the knife should be specified and can readily be tested. A soft knife can be easily honed and is tough but also wears rapidly. A hard knife is difficult to hone, is more likely to chip if it hits something hard, but holds a sharp edge much bettel·. Most rotary veneer plants prefer a knife with a Rockwell hardness on the C scale of 56 to fi8. Knives for face veneer slicers are often 58 to 60 on the Rockwell C scale. To keep as sharp an edge as possible ,,'hen cutting low-density woods like basswood, a knife \\'ith a Rockwell hardness of 60 to 62 may even be used. Bevel angle, wedge angle, and sharpness angle all refer to the angle that results from the intersection of the two surfaces which form the knife edge. This and other terminology used with the knife and pressure bar are shown in figure 19. The knife bevel angle may vary from about 18° to 23 0 • The smaller the angle, the less the veneer is bent as it is cut and hence the tighter the veneer. In contrast, the larger the bevel angle the stiffer the blade and the better the edge can withstand impact. More care must be taken 'when grinding the smaller bevel angles as the knife tip is more likely to heat than when grinding a knife to a large bevel angle. An 18° bevel angle may be used to slice prop­ erly heated flitches of eastern redcedar while a 23 ° bevel angle is often used to rotary cut bolts of unheated softwoods. Many veneer knives are ground to a bevel angle of 20°01' 21 0. Some lathe and slicer operators prefer to measure the length of the knife bevel rather than the knife bevel angle (fig. 19). Some rela­ tions of knife thickness, knife bevel angle, and knife bevel length follow: The knife represents the largest maintenance cost in cutting veneer and consequently it is worthwhile to use good purchasing specifica­ tions and take care in grinding and setting the knives in the lathe or slicer. What should be specified when ordering a knife for the lathe or slicer? The length of the knife and presence or absence of slots and their spacing wili be determined by the equipment on which the knife will be used. Other factors such as depth, thickness, hardness, insert or solid, and the grind can be specified. In addi­ tion, the percent caruon and other components of the steel could be specified. However, the exact components of the knife steel are gener­ all;y not published by knife manufacturers. As a result, most veneer plant managers deal with a reputable knife manufacturer and specify only the size, shape, hardness, and whether they 'want an insert or solid blade. An ideal knife should have maximum stiffness, tough­ ness, corrosion resistance, and wear resistance. The most common knife thickness for lathes is r.~ inch (16 mm), and for face \E'neer slicers, :)1 inch (19 mm) . Thinner knives such as I~ inch (13 mm) are sometimes used on the lathe; they are less expensive but also less stiff. The Euro­ pean horizontal slicers may use a knife II':I!! inch (15 mm) in thickness, supported with a blade holder. In general, the Veneer knife should be thicker when cutting thick veneer. When cut­ ting thin veneer, thinner knives can be used jf they are properly supported. The choice of an inlaid knife or one hardened throughout may depend on the end product. Hardwood face veneer is generally cut with an inlaid knife. The mild steel used for backing- is stable and easy to grind. It can be readily drilled so that the knife can be held firmly when back grinding. The highly l'efinec1 hard­ ened tool steel insert is generally of highest quality for cutting 'wood. Knives that are hardened throughout report­ eclly may stand up better when cutting hard knots. They are sometimes, but not al ways, used in plants producing construction plywood. 54 Knife Thickness Knife Bevel Angle Knife Bevel Length Inch DegTee.~ Inch 1/2 (0.500) 18 19 20 21 22 23 18 19 20 21 22 23 18 19 20 21 22 23 1.618 1.536 1.462 1.395 1.335 1 ..280 2.023 1.920 1.827 1.744 1.668 1.600 2.427 2.304 2.193 2.093 2.002 1.919 5/8 (0.625) 3/4 (0.750 \ The ground surface is generally slightly con­ cave to make the knife easier to hone. For the lathe, the recommended hollow grind is 0.002 to 0.004 inch (0.05 to 0.10 mm) while slicer knives generally have a hollow of 0.001 to 0.002 inch (0.025 to 0.05 mm). The flatter grind for a slicer knife means less chance for the flitch to rub against the heel of the knife and stain the wood. More hollow can be used on a lathe knife as the bolt surface curves away from the ground surface of the knife. However, the hollow should not exceed 0.004 inch (0.10 mm) as this weakens the knife edge. While the details of the knife bevel can be changed by grinding at the veneer producing plant, the knife should be ordered as it will be used to eliminate an extra grinding. Knife Wear Knife wear apparently takes place by three methods: Impact, abrasion, and cOlTosion. Im­ pact and abrasion are mechanical phenomena while corrosion is chemical in nature. Mechanical impact is most obvious when a hard object, such as a small piece of gravel, chips the knife edge. Damage due to mechani­ cal impact may also occur when the knife hits hard, unheated knots. Such knots may turn the extreme edge of the knife. Woods containing 1 percent or more of silica or calcium carbon­ ate are abrasive and rapidly wear a rough edge on a veneer knife. Use of a tough tool steel rather than a brittle steel may help reduce the damage due to mechanical impact. Use of a microbevel (10) Or back bevel reduces the chance of damage due to impact and may make it possible to cut abrasive wood longer between honings. A microbevel about 0.015 inch wide is often applied at the edge of the knife to make the included angle about 30° (10). If a tough knife could be made from tungsten car­ bide ground to a 20° included angle, this should be a good material for cutting wood containing silica or calcium carbonate crystals. The third method of knife wear is corrosion as described by Kivimaa (31) and by McKen­ zie and McCombe (47). Acetic acid and poly­ phenols in some woods react with the steel knife and corrode it. This reaction makes the common blue iron stain that is so objection­ able on face veneer as well as causing wem' of the knife. Kivimaa (31) fO'.lnd that knife wear was greatly retarded by putting a positive potential on the wood ·work piece and a nega­ tive potential of 1,500 volts on a planer knife. Later at Madison we put a positive charge of 300 volts on a rigid pressure bar on a lathe 4 feet (1.2 m) long and a negative charge on the knife. The charge greatly retarded blue stain from the knife as compared to the stain that developed on oak veneer '."hen the lathe was stopped momentarily without a charge to the pressure bar. However, a shallow brown stain OCCUlTed on the veneer next to the knife. In addition, blue stain from the tool steel pres­ sure bar became worse. When a stainless steel pressure bar was used, the blue stain was nearly stopped next to the bar but the shallow brown stain again occ1.llTed on the wood next to the tool steel knife. Ralph Scott, a research chemist at the U.S. Forest Products Labora­ tory, checked the wood next to the knife (nega­ tive terminal) and found it to be a strong base (pH 10 to 12). Apparently hydroxyl ions were released at the negative terminal and formed a base that turned the wood brown. Another difficulty with running 300 volts direct current from the pressure bar to the knife was that sap forced from the bolt ends made a short and the arc caused a big crater in the knife at this point. A third problem was that the stain was spotty over the 4-foot (1.2 m) length of veneer, indicating the electric cur­ rent took the path of least resistance and so was not acting unifornly to reduce stain and knife wear. McKenzie and McCombe U7) successfully rotary-cut bolts 4:lj inches (12 cm) long "with 55 the knife held at a negative potential of 60 volts with respect to the nosebar. They report that knife wear was reduced 60 percent. In spite of the difficulties in applying a posi­ tive electrical potential to the bolt or flitch and a negative potential to possibly both the knife and pressure bar, tIl(> method does look tech­ nically interesting. An alternative would be development of stainless knives than can hold an edge sharp enough for good veneer cutting. Grinding Veneer Knhles The purpose of grinding is to restore a straight, sharp, tough edge. If these three re­ quirements are kept in mind, they may help guide good grinding practice. In order to grind a straight edge, it iR neces­ sary to start with a rigid level grinder. The most satisfactory veneer knife grinders have a fixed bed for mounting the knife and a travel­ ing grinding wheel. The abrasive may be a soliel cup wheel or a segmented wheel. Some operatorR prefer the segmented wheel because it requireR less dress­ ing and replacement segments are leRs expen­ sive than a new cup wheel. A magnetic chuck nakes it faster to set the knife for grinding. A V-belt drive in place of gears reportedly reduces chatter marks on the knife. The knife bed as well as the "ways on "which the grinder moves must be rigid, straight, and parallel to one another. The ways are generally hand scraped for accuracy when the grinder is made. The ways should have wipe~'s to keep them clean in use. The accuracy of the ways can be measured in the veneer plant by travers­ ing them with a dolly holding a gage. A special telescope with a measuring cl'osshair is leveled like a transit and then sighted On the gage on the dolly. The dolly is moved along the ways and any deviation from a straight line can be recorded. If the ways are not straight, they must be straightened at the factory. After the ways have been determined to be straight, they are used as a reference to determine if the knife bed is straight and parallel to the ways. This can be readily done in the veneer plant by indexing with a surface gagA, such as a dial indicator, from the grinding wheel carrier which moves on the "ways. If the knifebed is not parallel to the ways on which the grinding wheel traverses, the knife bed should be adjusted until it is parallel to the ways. To maintain even weal' of the ways, the grinding "wheel should traverse the entire length of the grinder even when grinding short kniyes. The surface of the knife that goes against the grinder bed must be checked for bumps or other rough spots that will prevent the knife from lying perfectly flat. If necessary, the back of the knife should also be ground to restore a plane surface. (See "Back Grinding.") Heat can cause metal to expand and deform. The grinder and knife should therefore be kept at as uniform a temperature as possible during grinding. An example of poor practice was a grinder set near a radiator. During summer the knife beel was straight. However, in winter with the radiator on, the grinder bed was heated on one side and warped enough to result in unsatisfactory grinding'. Similarly, the water used to cool the grinding wheel and knife should be at room temperature and be recirculated. A stream of ,vater with synthetic coolant should be directed against the grinding stone 1~ inch ahead of where the stone contacts the knife edge during grinding. Godin (24) considers overheating of the knife tip the most serious problem in grinding and lists four main causes: (1) Too heavy a cut; (2) inadequate cooling; (3) clogged grind­ ing wheel; and (i!) too hard a grade of grind­ ing wheel. Heating is less likely to occur if the knife edge is pointed up and engages the grind­ ing wheel first during grinding. A feed of 0.0003 to 0.0005 inch (0.0008 to 0.012 mm) is suggested for ea.ch complete traverse of the wheel. At the FPL we like to dress the wheel and use a very fine feed for the last one or two traverses of the sharpening. This helps give a fine surface. Some manufacturers polish the knife by multiple passes without feeding. The smooth edge reportedly aids good veneer cutting. Care must be used with this technique or the grinding wheel may rub, heat, and weaken the knife tip. Another cause of an irregular edge is dubbing at the two ends of the knife. The most likely causes are looseness in the grinding wheel spindle bearings, excessive end play, and slack in the feeding mechanism. However, even a 56 grinder in good mechanical condition may slightly round the ends of the knife. This may not be a problem as the end inch or two of the knife generally does not engage the wood 'when cutting veneer on a commercial lathe or slicer. If it is important to have the knife straight to the extreme ends, then dummy knife sections 4 to 6 inches (10 to 15 cm) can be attached to the knife bed at the two ends and in line with the knife being ground. Sections of a dis­ carded knife can be used for this. The dummy sections abi'orb the heavier cut at the start of each traverse of the wheel and the main knife is not dubbed at the ends. knife develops a heavy wire edge, the grinding 'wheel can be stopped and the wire edge removed while the knife is still clamped in the grinder. A few more passes of the wheel will create a new fine wire edge that can be easily removed by honing. After the wire edge is ren10ved, the edge is finished by lightly honing with a fine­ textured stone that has been stored in kerosene. More detailed suggestions for grinding and honing veneer knives are c:ontained in Cana­ dian Forestry Sen'ice Publication No. 1236 Back Grindin~ After a knife is used, it may wear unevenly on the side 'where the ,-eneer passes through the throat between the pres<;ure bar and the knife. It may also be bent by excessive local pressure as from a knot or chip buildup. This can be detected by placing a straightedge at a right angle to the cutting edge. If this surface is not fiat, then grinding the side of the knife that goes next to the bolt or flitch will not result in a straight edge. The solution is to grind a flat surface on the veneer side of the knife. The grinder bed is tilted':!o to 3" toward the knife and the knife is ground to produce a bevel 1~ to 1-1.i inches long. A magnetic chuck on the grinder facilitates this grinding. Other­ wise, the knife body must be drilled and tapped not more than 12 inches apart so the knife can be mounted securely for back grinding. Some modern grinders are equipped with two grinding wheels so the face and back of the knife can be ground at the same time. vVhen a sharp knife ground to a bevel angle of about 21 ° is first put in the lathe or slicer, it is easily nicked by a knot or other hard sub­ stance. These nicks are removed by honing the knife in place on the lathe or slicer. After sev­ eral bolts orf' 'tches are cut, the knife edge wears slightly and this, plus the honing, makes the extreme edge more resistant to damage. This condition is sometimes called a work-sharp knife. 'Vhen examined under a microscope, the edge is seen to be slightly rounded so it is probably closer to 30° to 3fi" than to 21 0 at the extreme tip. Such a knife will remain sharp and do a goocl job of cutting for several hours if no very hard material is hit. For other steel knives used to cut wood, such as planer knives, the smaller the bevel or sharp­ ness angle, the faster the knife wears. The rate of wear goes up much faster if the bevel angle or sharpness angle is less than 30" to 35°. This wear phenomenon is apparently the same for "eneer knives. Realizing this, the veneer indus­ b'~' has long had a practice of putting a back bevel on the knife. This strengthens the knife edge and is commonly used with knives installed on ('orE' lathes fol' peel i ng un heated softwoods. Kiviml:1l:1 and Kovanen (.J2) , Feihl (10), and others have studied the llse of a precision micro­ bevel put on either side of the knife. They report that a second bevel can be honed on either or both sieles of the knife, and that the final included angle of 30<' Or 3fio with a micro­ bevel (UnO to 0.020 inch in \ddth greatly im­ l))"o,'es the strength of the knife edge. At least one commercial grinder has a separate grind­ illg wheel that call grind a micl'obevel at the same time the main hevel is being ground. Some slice]' operators use a two-bevel knife. Honing Knife The knife should be ground only enough to obtain a thin wire edge the length of the knife. The wire edge is removed by careful honing with a stone on one si,te of the knife, then the other. The stone should be medium grain and medium to soft in hardness. The stone should be saturated with kerosene. Some operators use one stone and others use two stones, one on each side of the knife simultaneously. In either case, each pass of the stone cuts at the base of the wire edge and bends it away from the stone. After several passes, most of the wire edge will fall off. Honing is continued until all of the ",.ire edge is removed. If a badly nicked (.24) . S{~('ondarr 57 Knife Bevels The main bevel is 19° and the second bevel is 21 Grinding of the second bevel is continued until the length of the second bevel is about % inch. When cutting, this is the only part of the knife that rubs against the flitch, and so the two-bevel knife reduces stain. Some opera­ tors like the two-bevel knife and others do not. 0. Setting Knife Information on setting the knife and bar in a lathe assumes that the knife frame and bar frame of the machine are in proper alinement with the center of rotation of the spindles. Similarly, it is assumed that the knife and bar ways on the slicer are level and perpendicular to the flitch way~. It is further assumed that there is a minimum of play in the moving parts of the lathe or slicer and that the machine parts are at the same temperature they attain in use. If these conditions are not met, the care­ ful setting of the knife and bar on the static machine may be changed so much in the dy­ namic cutting condition that poor quality veneer will be produced. Feihl and Godin (15) de­ scribe methods of checking the basic alinerilent of lathes. Setting the Knife in the Lathe and Slicer A correctly ground flat knife with a straight cutting edge is the first requirement. If a knife holder is used, it must also be clean and flat. A clean, flat bed on the lathe or slicer is the second requirement. (If these conditions are not met, it is difficult or impossible to correctly set the knife.) The knife or knife and knife holder is then set on the two end adjusting screws. The clamping screws are tightened by hand so that the knife is flat against the bed but free to move. To this point, the procedure is the same for the lathe and the slicer. Setting the Lathe Knife After the knife is resting on the two end adj usting screws on the lathe, the knife edge is raised until it is level with the center of the spindles. This can be facilitated by using a template consisting of an accurately machined wood block cut out at one end to one-half the diameter of the spindle. The cutout end rests on the spindle and the other end on the knife edge. The height of the knife is then adjusted until a spirit level on the back of the template indicates level. The same adjust­ ment is then made at the other end of the knife. If the span is short and the knife deep and stiff, the knife height should be the same across the lathe. However, with longer knives, particularly those that have been ground so they are not so deep, the knife may sag in the middle. One way of checking this is to level a transit with a telescope about 20 feet (6 m) from the lathe and s·wing it from one end of the knife to the other. The knife edge should be in line with the crosshairs along its length. If the knife sags in the middle, it should be raised with the leveling screws near the center of the knife. Once the knife edge is true, some opera­ tors make scribe marks on the lathe so they can reposition knives with precision. Another method is to measure the extension of the knife from the top of the knife bed. To speed up knife changes, some lathes have knife holders. After grinding, the knife is pre­ set to the desired height in the holder. and the holder quickly bolted in place in the lathe. Some plants in effect preset the knife by pouring babbit metal at the bottom edge of the knife after each grind. The depth of the knife is thus kept constant and the knife can then be placed on the height-adjusting screws without chang­ ing them. Sag in the knife can also be checked with a tautly stretched fine wire. If there is wear in the spindle bearings, the bolt will ride up during r.utting, taking up the play. To compensate for this, the knife edge is sometimes set above the spindle centers the same amount as the play in the spindles. This results in the knife edge being at the spindle centers during cutting. After the knife is set to the spindle centers, the knife angle is adjusted. In general, the side of the knife that contacts the bolt is ap­ proximately vertical (tangent to the surface of the bolt). Such a knife is said to have an angle of 90°. If the knife leads into the bolt 2°, the knife angle is 92° and the clearance angle 2°. A lathe knife can also be set with a negative clearance. A knife angle of 89° means the knife has 1 ° negative clearance. Most lathes are built so the knife angle can be made to change automatically with the bolt diameter. The objective is to keep the width of the knife surface that rubs against the bolt 58 about the same when cuttinp- a bolt of a large diameter as at a small diamete1'. For example, when cutting at a bolt diameter of 3 feet (91 cm), the knife angle may be 91 0 ; at a diameter of 6 inches (15 cm) the angle may be 89 0 30'. The means of changing the knife pitch varies with different lathes. Feihl and Godin (15) describe several methods that can be used to properly set the pitch ways. The lathe manu­ facturers should be consulted for recommended procedure for use with their lathes. In general, lathe operators use less lead into the bolt (1o\\'e1' knife angles) ,v'hen cutting low­ density woods than when cutting thick veneer. For example, Fleischer (17) suggests a knife setting of 90 0 30' when cutting J11~-inch (0.8 mm) yellow-poplar (low-density wood) and 0 90 45' when cutting l1j~-inch (0.8 rom) ;Veno,," birch (high-density wood). Fleischer sho'ws a pronounced effect of veneer thickness on the best knife setting. For 1,t(}(l-inch (0.25 mm) birch, he recommends a knife setting of 92 for JI;I~-inch (0.8 mm) 90 0 45', for lIin-inch (1.6 rom) 90 15', and for \:"-inch (3.2 mm) veneer 0 90 • These settings a1'e for log diameter from 20 to 12 inches (50 to 30 cm). When the correct knife angle is being used, the knife side next to the bolt will show It,n to V· inch (1.6 to 3.2 mm) of bright rub below the knife edge. If the correct knife angle is not used, the veneer may show this. Too high an angle causes the knife or bolt to chatter and results in a corrugation on the veneer and the bolt surfaces. The waves are closely spaced with three 01' mOl'e waves per inch of veneer width. Too low a knife angle results in too much bearing on the knife, forcing it out of the ideal spiral cutting line. When the fOl'ce on the knife builds up, it may then plunge into the bolt, resulting in thick and thin veneer with 'waves a foot or more apart. Some lathe operators use low knife angles, as the heavy bearing of the knife against the bolt tends to smooth the surface of the veneer. Lathe and knife manufacturers do not Uke this practice because the pressures on the face of the knife may become so great that the knife wHI be bent and the knife failure blamed on the knife manufacturer. Low knife angles also require more power for tu·rning the bolt and cause mOl'e stain and wear to the lathe. 0 , To prevent these problems, some lathe opera­ tors increase the angle of the knife until a corrugated veneer surface results. They then reduce the knife angle gradually until the cor­ rugations disappear and use this .Knife angle for cutting. For best results, \\'e recommend determining and recording thl) knife angles that are satis­ factory and usinr; an instrument for measuring this angle when the knife is set. Instruments for measuri ng the knife angle are described by Fleischer (1,9) Feihl and Godin (15), Fondronniel' and Guillerm (21), and Dokken and Godin (9). ,\Vhile all are suit­ able, the French design (21) (fig. 21) and the Canadian design (9) are easily read. If the knives are all ground the same, they can be interchanged on a lathe or slicer with­ out changing the knife angle or clearance angle. However, if the knives are ground so the bevel or sharpness angle is as little at 1~0 different, the cutting can be altered significantly. Conse­ quently, we recommend the knife angle be t 0 59 :/[ L311 !l311 FigurE' 21.-1nstrument of French drsign for lllHaSUl'­ ing L1lE' knifr angle. It is held by magnets to thr facE' of the knife, the bubble is centered, and the knife angle is read on the vernier. checked with an instrument after each knife change. Setting the Slicer Knife Setting the knife ill the slicer is similar to setting the knife in a lathe except that the position of the knife edge in a slicer is set by the extension of the knife from the bed. Th'e slicer knife edge should extend above the knife bed just enough so the ground face of the knife clears the bolts that hold it against the knife bed. In other words, the knife should extend as little as possible and still make certain the flitch 'will clear. On vertical face veneer slicers, this distance is about 2 inches. Like the lathe knife, the slicer knife shouldl'est on the two end adjusting screws. The knife is then brought against the bed and an~r sag in the middle is removed with the height-adjusting screws neal' the middle of the slicer. Since slicer knives are often longer than lathe kni'i:es, this adjustment is more critical on the slicer. A taut fine wire can be used as a guide to deter­ mine sag in the knife or, if the pressure bar bed is known to be straight, it can be used as a guide. A preSSUl'e bar that has been ground uniform in thickness is braught up against the pressure bar bed. The bottom of the preSSlll'e bar can then be used as a reference to deter­ mine if there is a sag in the slicer knife. Once the knife edge is determined to be straight, the knife is bolted nrmly in place and all of the adjusting screws are brought in con­ tact with the b0ttom of the knife. The knife angle of the slicer is relatively easy to set compared to the lathe knife, Sinc~ all cutting is from a flat smface, the knife angle does not change with flitch diameter. Further, the knife must lead into the flitch so the heel of the knife does not rub hard against the flitch. Experimentally, we have found that a slicer knife angle from 90° 20' to 90° 30' (about 1'2° clearance angle) can be used to slice wood from %lO to I; inch (0.25 to 6.3 mm) in thickness from both low-densit~T and high­ density woods. Like the lathe knife, the angle of the slicer knife should be checked ,Yith an insh ument each time a knife is replaced. Pressure Bar The pressure bar is important for control­ ling thickness, smoothness, and depth of checks into the veneer. It compresses the wood just ahead of the knife and so al10ws the knife to cut rather than split the veneer from the bolt or flitch. This helps control rough surfaces and checks into the veneer. By keeping a force be­ tween the knife carriage and the flitch or bolt, the pressure bar takes up slack in the machin­ ery always in the same direction and so aids control of the veneer thickness. There are two common types of pressure bars -the nxed pres~ml'e bar and the roller pres­ sure bar. Fixed Pressure Bar Two factors to consider when selecting a fixed pressure bar are its stability and wear resistance. The most common metals are tool steel, stel1ite, and stainless steel. The tool steel bar is relatiyely stable, machines easily, and is relatively inexpensive. A stellite bar is more expensive, harder to grind, and less stable. However, the stellite bar ""HI wear many times longer than the tool steel. Stainless steel is easier to grind than stellite and, like stellite, does not stain the veneer. The nxed bar is generally ground to a bevel angle of about 74 0 to 78°. As the wood bolt or flitch approaches the nxed bar in the lathe or slicer, the wood is compressed along a plane 12° to 16° from the motion of the wood. When cutting 1~" inch (0.9 mm) or thinner veneer from dense hardwoods, the bar should be ground to a sharp edge. The edge of the bar is generally slightly eased or rounded when cut­ ting thicker veneer from low-density woods 01' "'oods subject to rupture on the tight side of the veneer from rubbing against the bar. Yari­ ous researchers recommend an edge radi us of about 0.015 inch (0.3 mm). But Fleischer (17) reports rounding the bar to '11;-inch (3.2 mm) radius did not improve the smoothness of west­ ern hemlock veneer and may be disadvan­ tageous. Roller PreSSllrl> Bar The roller bar is the second major type of presslire bal'. In U.S. practice, the bar is com­ monl~T of bronze, generally r,!~ inch (15.9 mm) in diameter if it is a single bar and I~ inch (12.7 mm) in diameter if it is a double roller bal'. The single 1'ol1er bar is driven directly while the double roller bar is driven with a 60 backup roll. Two advantages of the double roller type stand out: (1) The drive roller can be larger so there is less breakage of the rollers, and (2) the knife and pressure bar can advance very close to the Chucks, permitting peeling to smaller diameter cores than with a single l'oller bar. The drive chain for a single roller bar may protrude up to 1 inch beyond the surface of the roller bar. Roller bars are generally lubricated with 1 percent vegetable oil mixed in water and introduced through holes in the cap that holds the bar. position of the bar with respect to the knife is fixed if any two of the three openings are fixed. For example, if the lead and gap are set, this also automatically sets the exit gap. \'~hich two are chosen for setting the knife and bar should depend on the ease with which the openings can be measured and on how the knife and bar can be adjusted on a specific lathe or slicer. Examples of how these three openings are interrelated for different veneer thicknesses and different settings are given in tables 8 thl'ough 11. Comparison of.Fixed Bar and Roller Bar Setting Fixed Pressure Bar on Lot.he (by 1'.ead and Gap) The fixed bar is the simplest and most com­ monly used pressure bar. It is used exclusively on slicers and is by far the most common bal" used to cut hardwoods on a lathe. The roller bar is more common in the United States for cutting vVest Coast softwoods and has occa­ sionally been used to cut eastern softwoods and hardwoods. The fixed bar can be used to cut veneer of any thickness. The 5~-inch (15.9 mm) diameter roller bar cannot be set to cut veneer much thinner than 1'1n inch (1.6 mm). Most veneer peeled with the aid of a railer bar is llsed in construction plywood and is li:! inch (2.1 mm) or thicker. In general, it is easier to set a fixed bar precisely than a roller bar. A major advantage of the driven roller bar is that it l'equires Jess torque to turn a bolt; this in turn means less spinout of the bolts at the chucks and Jess bl'eakage at shake and splits in these bolts. Another advantap:e of the roller bar is that it pushes through sman splinters that otherwise may jam between a fixed bar and the bolt and degrade the veneer. Setting Pressure Bar The information on setting the pressure bar, like the information on setting the knife, assumes the lathe or slicer is in good mechani­ cal condition ,dth a minimum of looseness in moving parts. The kllife, pressure bar, and surroundjng metal parts on the lathe or slicer should be at the approximate temperature they 'will attain during cutting. Cross sections of the knife with a conven­ tional fixed bar and a roller bar are shown in figure 19. Three openings between the knife and the bar are indicated-the lead, gap, and exit gap. Wif:h any knife-bar combination, the 61 \"Then the knife edge and the pressure bar edge are ground straight, it is much easier to set the bar. These two edges must be straight and as perfectly ~t1ined as posible for precision veneer cutting. All the precautions suggested under knife grincUng should also be used when grinding a new edge on a fixed pressure bar. The bed for the bar and the nosebar cap should be clean and straight. The bar is in­ serted between the beel and the cap and the nosebar locking screw tightened just enough to hold the bar against the bed but loose enough so the bar can be moved without bending it. The bar should extend from the supporting casting only a minimum amount so it is a rigid as practical. After the knife is set, the bar is moved toward the knife with aajusting scre\\'s at the two ends of the bar untj] the bar is about lic' inch (0.8 mm) behind the knife edge. Settin~ Lead The nosebar bed On most lathes has adjust­ ing screws at the two ends that allow the entire bed to be raised or lowered, increasing or de­ creasing the lead of the nosebar edge ,dth respect to the knife edge. The amount of lead (vertical opening) is adjusted primarily for the thickness of veneer being cut. Some lathe operators set the lead one-third of the thick­ ness of veneer being cut. Fleischer (17) sug­ gests there is a straight-line relationship with a lead of 0.0005 inch (0.12 mm) when cutting ~ill() inch (0.25 mm) and a lead of 0.030 inch (0.8 mm) when cutting 1 s-inch (3.2 mm) veneer. Some settings using a variable lead that depend on veneer thkkness are shown in table 9. Certain lathes made in Germany do not Table 8.-Lathe settings tvith a fixed bar and a constant lead 1 ------------------------ Feed (veneer thickness) In. 0.010 .032 .042 .0625 .100 .125 .1875 .250 I j\lhn Mm In. 0.030 .030 .030 .030 .030 .030 .030 .030 0.25 .81 1.07 1.59 2.54 3.17 4.76 6.35 Exit gap Gap Lead Mm In. 0.009 .029 .038 .056 .090 .112 .1(,9 .225 0.76 .76 .76 .76 .76 .76 .76 .76 In. 0.019 .038 .046 .063 .095 .115 .168 .221 0.23 .74 .97 1.42 2.29 2.84 4.29 5.71 Mm 0.48 .97 1.17 1.60 2.41 2.92 4.27 5.61 Fixed bar, knife bevel 20°, knife angle 90° (0° clearance), lead 0.030 in. (0.76 mm), and gap 10 pet less than feed. Table 9.-Lathe settings tcith a fixed bar and a variable lead Feed (veneer thickness) In. 0.010 .032 .042 .0625 .100 .125 .1875 .250 Lead 111m Gap M7It In. 0.005 .010 .012 .017 .024 .030 .043 .056 0.25 .81 1.07 1.59 2.54 3.17 4.76 6.35 1 llfm In. 0.009 .029 .038 .056 .090 .112 .169 .225 0.13 .25 .30 .43 .51 .76 1.09 1.42 Exit gap ._-In. Mm 0.010 .031 .040 .058 .093 .115 .173 .230 0.23 .74 .97 1.42 2.29 2.84 4.29 5.71 0.25 .79 1.02 1.47 2.36 2.92 4.39 5.84 --,-~-----. I Fixed bar, knife be"el 21°, knife angle 90° (00 clearance), lead changing with veneer thickness (13), and gap 10 pet less than feed. Table lO.-Lathe settings with a roller bar and a fixed lead 1 Feed (veneer thickness) In. 0.0625 .100 .125 .1875 .250 Mm Mm In. 0.085 .085 .085 .085 .085 1.59 2.54 3.17 4.76 6.35 Gap Lead hi. 0.056 .090 .112 .169 .225 2.16 2.16 2.16 2.16 2.16 15 ''R-in.-diameter roller har. knife hevel 20°. knife angle 90 0 (00 Exit gap Mm 1.57 2.39 2.90 4.24 5.59 c1earancel, lead 0.085 in. (2.16 mm), and gap 10 pet less than feed. Table n.-Lathe settings with a roller bar and a variable lead Lead Feed (veneer thickness) In. 0.062 .094 .114 .167 .220 111"711 1.42 2.29 2.84 4.29 5.71 1 Gap Exit gap ....----~-~----. In. 0.0525 .100 .125 .1875 .250 Mm 1.59 2.54 3.17 4.16 6.35 _ _ .4-~" _ _ _ _ _ ~_~" _. _ _ _ _ _ _ _ ,-_~ In. 0.068 .075 .079 .089 .100 In. 0.056 .090 .112 .169 .225 MlIt 1.73 1.90 2.01 2.26 2.54 ~-~_~._ Mm 1.42 2.29 2.84 4.29 5.71 "--~---.------- I 5!8-in••diameter roller bar. kn;fe bevel 21 0 , knife angle 90 0 (00 clearunce), gap equal exit gap equal 10 pet less than feed. 62 In. 0.056 .090 .112 .169 .225 Mm 1.42 2.29 2.84 4.29 5.71 have a lead or vertical-opening adjustment. This distance is built in the lathe to be about 0.020 inch (0.5 mm). It coincides -with the lead suggested by Fleischer for cutting veneer about 71-1 inch (2 mm) thick. All agree that the bar edge should be set above rather than at or below the knife edge. It is also generally agreed that the distance the bar is set to lead the knife must be the same at all points along the knife edge. The common method of checking this opening is to insert a feeler gage of the proper thick­ ness in the Jead (fig. 22) between the knife edge and the bar. When the feeler gage is per­ pendicular to the ground face of the knife, the opening is the same as the thickness of the gage. After the bar is set this way at both ends, it should also be checked at other intervals along the knife. Some lathes have push-pulls so the bar can be warped locally to make the Jead or vertical opening uniform across the lathe. However, if the knife and bar are ground straight and the knife bed and bar bed are also straight, any local adjustment of the lead should be minimal. Use of a feeler gage may slightly nick the blade. It is, therefore, good practice to lightly hone the knife after setting the lead. Setting the Gap The second bar adjustment is the gap or horizontal opening. This is the distance from the leading edge of the pressure bar to a plane extended from the ground surface of the knife. Some experienced operators like to bring the edge of the bar to the same plane as the knife edge. Then by feeling with the thumb, they can tell jf there are any spots whel'e the bar is ahead or behind the knife edge. These local spots are brought in line with the push-pull screws at the back of the bar. Once the bar is "fit" to the knife, it is retracted to give the desired opening or gap and clamped. vVe prefer to use instruments to help make this critical setting. Two such instruments are described by Fleischer (19) and Feihl and Godin (15). Both are essentially dial-microm­ eter depth gages that use the ground surface of the knife as a reference and measure to the edge of the bal'. To automatically position the measuring pin, Fleischer (19) suggests that M 139 !)42 Figure 22.-Adjusting the lead of the pressure bar with a feeler gage: The lead of the b~r,is moye(~ until a fe~ler gage of the desired thickness is at a right angle to the face of the kmfe when the gage IS lTIserted In the opening between the knife and the bar. 63 1'.1 13~1 ~I tn L~"jr" :.::;, l,a)' :\1,'a~lJr:l'g till' ~a), ;",1\\,"')1 tllf' kllif,' alll\ pl'('~~Ul'!' \,ar p(h;('. :\1"[I"\ll'!'l1l1'l1t,; al'l' !'!lHlI",d on til,· !lll"", .'a-til:g alld :1!1;. df'\;:l~:,q:, ).':!'.. al,'1' titall 11.11111 ill('h l'I'lll<>\'"d with tlw l'u:('('IPs that i:-; I'P"j,;tant (II damap:p h,\' s(,],:tpiIlJr t lip 111I,;el"u' IIn']' the \\,(llld ,;urfa('p. It is po:-;,;il>lp the ~() pe]'('elll figun) l11a~' haw bpell (jPl'i\'erl from J1Iea,;ul'l'Il1Pllb (Ill [aU IPS that had some l()():-;(,Ile,.;~ or play ane! not co]'recting fo/, t he lo():-;elle~s, \\'hen the Jll'e';~lll'e hal' is ~et ai' (jl':-;( rilJ('(l ('arliPl' \\'P ha\

in..;! nnnellt l'e4 Illl the till' or the jl]'C':-;:-;ure hal' :Illf! 1111 the gTIll!llcl f;J('e of the knife (fig. ~:}) . \\'hllp 011(' mall hold...; the ill:::tl'ument ill COll­ tact \\itll the kllij'p alld the lllEl\'ahle :-;ell:-;ing pitt agaill,..;t 11,P lpadillg' 111l~l'ha]' edge. a :-;eculld III a I I ar!\'1l lliolmted 'II! tIll' !:tUtl'. tht- g'ap ,.;!tolllcl ]11)\\' jH' tlw,all'l> ;II'I'IJ,,"- tIll' latll(', JlO\\I,·n·l'. ,... jllc'P Ihi" i,'-> oIH, .. r tllp .-ril i,'at Iathp "p(liug·,.... \\p routinely ,·11(" kiLl' "PPllillg 01 ,lfap Ht l-illC'h illtpl'\'ab alllng 1II{' 1';11', 'I'Ll' y;t!lW of eal'll rpading j:-; I'\wlkl't\ ,'11 tll(' ca,.;tillg' Il'ddillg thp l'rp,";~lIre 1mI'. Al:~ gl'wlua: l,elid ... "I' liulllp" ill thp l,al' arC' thPll 1,laiI11~' \'i"jlik L(wal dl'\'iatioll'; an' (,01'­ (-i1 cutting thinner veneer. Higher compression (smaller gap or horizontal opening) may re­ sult in tighter veneer; it may also cause the veneer to be thinner than the knife feed and cause damage to the tight side, such as shell­ ing of the grain on susceptible species like western redcedar and redwood. The advantage of using instruments to meas­ ure the knife angle and pressure bar settings is that the setup can be readily duplicated. When experience shows that a certain setting is good for cutting a given thickness of veneer from a given species at a given temperature, then the information should be recorded and the exact processing conditions duplicated when this item is produced again. Setting Fixed Pressure Bar on Slicer (by Lead and Gap) The slicer bar is ground and set by the same method as described for setting the fixed bar on the lathe. The difference cornes in the actual value of the settings. On the lathe, the lead or vertical opening may be set at various openings such as 0.010 inch (0.25 mm) for~~o-inch (0.5 mm) veneer to 0.030 (0.75 mm) for %-inch (3.2 mm) veneer. On the slicer, the lead or vertical opening is generally set at about 0.030 inch (0.75 mm). We have cut veneer of satis­ factOl-y quality from l/tOO to 111 inch (0.25 to 6.3 mm) in thickness with this lead. A smaller lead such as 0.020 inch (0.5 mm) can be used when cutting l dh -inch (0.9 mm) and thinner veneer. However, this smaller lead may result in more splinters breaking off at the end of the cut and more chance that splinters will become jammed between the knife and bar, causing rub mal'l<;:s on the veneer. Not as much pressure can be applied with the nosebar on a vertical operating face veneer slicer as can be applied on a lathe. The knife and pressure bar rest on half bearings, permit­ ting the knife and bar to be offset to clear the flitch on the upstroke. If the pressure bar is set for excessive pressure against the flitch, it will cause the knife and bar carriage to rock on the half bearing; the result is poor veneer and possibly damage to the slicer. When slicing 1!!s-inch (O.036-in.) (0.9 mm) veneer, we have found the range of satisfactory gap or horizontal openings between the knife and bar to be between 0.029 and 0.032 inch (0.725 and 0.800 mm). In effect, the bar is then compressing the ·wood just ahead of the knife edge 0.004 to 0.007 inch (0.1 to 0.175 mm). Face veneer producers sometimes set the bar to compress the wood only 0.001 or 0.002 inch. When slicing thicker veneer such as % (0.125) inch (3.25 mm), the bar may be set to leave a gap of 0.115 inch (2.95 mm), or 0.010 inch (0.25 mm) less than the feed. As with the lathe, more compl'ession (slightly smaller openings) can be used when cutting low-density woods than when cutting high­ density woods. Setting Roller Pressure Bar on Lathe (by Lead and Gap) The roller bar is most commonly used when rotary-cutting western softwoods Yl!! to :}j(j inch (2.1 to 4.8 mm) in thickness. It is not suitable for cutting veneer thinner than ¥tu inch (1.6 mm). The reason is that the pressure should be applied against the bolt just ahead of the knife edge. When cutting veneer thinner than l;io inch (1.6 mm), a roller bar set at a fixed bar lead would over-compress the veneer after it is cut by restricting the throat between the roller bar and the knife. This restraint may cause the veneer to jam and break. In industry practice, %-inch- (15.9 mm) di­ ameter roller bars are generally set ·with a lead of lito (0.062) inch (1.6 mm) or more. From theoretical considerations and laboratory ex­ periments, Feihl, Colbeck, and Godin (13) recommended a roller bar lead or vertical gap of 0.085 inch (2.16 mm) when cutting Douglas­ fir ~"o to ~'1 inch (2.54 to 6.35 mm) in thickness. They also describe an instrument for measur­ ing the lead of a roller bar. Lathe settings for several veneer thicknesses using a fixed lead are shown in table 10. The gap is set much the same as with a fixed bar. That is, good results are obtained by com­ pressing the wood ahead of the knife about 10 to 15 percent of the veneer thickness. This varies with species, wood density, and veneer thickness as discussed under the fixed pressure bar. The gap or horizDntal opening can be set and checked with a depth gage reading to 0.001 inch (0.025 mm). 65 Setting Roller Pressure Bar (By Gap and Exit Gap) Collett, Brackley, and Cumming (7) suggest that lathes having a roller bar be set by gap and exit gap. They comment that, for veneer thicknesses from llro to 1/[ inch (2.54 to 6.35 mm), the literature indicates that the gap and exit gap can be the same. This simplifies the recordkecping as unly one value needs to be recorded for each veneer thickness of each species. They recommend use of a depth gage to measure the gap and a feeler gage to measure the exit gap. The amount of compression they suggest at both the gap and exit gap is 10 to 20 percent of the veneer thickness. Table 11 shows some settings whel'e the gap and exit gap are the same. Setting Fixed Pressure Bar (By Lead and Exit Gap) Lead and exit gap are suggested by Fondron­ nier and Guillerm (21) as the openings to be measured when setting a lathe with a fixed bar. They list the lead changing in a regular man­ ner with veneer thickness as follows: the bar. They report that the method elimi­ nates play in the horizontal mechanism; pro­ vides a direct measure of pressure against the bar and so gives the operator good control of the setting; and finally that the veneer pro­ duced was equal in quality to veneer produced with a bar set to fixed stops. The method is being tried commercially. Possible Ways to Generalize Setting of Lathe and Slicer Optimization of veneer peeling or slicing may require different knife and pressure bar settings for each specific cutting situation. However, it would be convenient to have one knife setting that could be used to cut veneer of any species into any thickness from l!:l~ to % inch (0.8 to 6.3 mm). Similarly, it would simplify pressure bar settings if one lead could be used for cut­ ting all veneer. From an examination of the literature and our own experience, it is possible to do this. Setting Gap by Pressure Rather Thall to Fixed Stops Generalized Knife Settings The knife settings specified in figure 24 are broadly applicable, and may be particularly valuable as a starting point for cutting un­ familiar species. The knife should be ground to a 21 0 bevel with 0.002-inch (0.05 mm) hollow grind. The knife angle can be set to 90 0 30' or, stated another way, with 1/~0 clearance angle. For lathes having an automatic change of knife angle with change in bolt diameter, the knife can be set at 90 30' when it is 12 inches (30 mm) from the spindle center. This knife set­ ting can be used to cut veneer %~ to ~" inch (0.8 to 6.3 mm) in thickness from any species on the slicer 01' on the lathe from bolt diameters of 24 inches (60 cm) to a 6-inch (15 cm) core. During rotary cutting of veneer, the force against the pressure bar may vary as much as from 10 to 500 pounds pel' lineal inch (178 to 8,900 kg/m) of contact -with the wood (.1;.5). Feihl and Carroll (12) adapted a research lathe to allow the bar to float and maintain the gap by pressme delivered by a cylinder and piston acting against the bar frame. In other words, they set the lead to stops but allowed the gap to be determined by the force against Generalized Setting of (l Fixed PresslLre Bar The pressure bar should be ground to have an included angle to 75°. This results in the woodwork piece being compressed along a plane approximately 15 0 from the cutting direc­ tion. The edge of the bar that contacts the wood should be rounded to an edge having a radius of about 0.015 inch (0.3 mm). Veneer Thickness (in.) 0.039 .078 .118 .157 .197 .236 (mm) 1 2 3 4 5 6 Lead 01' Vertical Opening (in.) (mm) 0.020 0.5 .024 .6 .028 .7 .031 .8 .035 .9 .039 1.0 They suggest the exit gap should be 10 to 20 percent less than the veneer thickness. Further they recommend that feeler gages be used to measure both the lead and exit gap. 0 66 F I I Ir- I I c I I KNIFE AND FIXED BAR C I KNIFE AND ROLLER BAR M 144 168 Figure 24.-Knife and pressure bar settings of general applicability are specified in terms of the diagram. These settings might be used to cut ven~er from V3!! to lA inch in thicknp.sR. Symbol A B C D Generalized Settings Symbol Knife angle = 90· 30' Knife bevel = 21 with 0.002-inch hollow grind Clearance angle = 30' (%.) Lead = 0.030 inch for fixed bar or 0.085 for %-inch-diameter roller bar E F 0 G H 67 Generalized Settings PressUl'e bar bevel = 75· Gap = 90 percent of veneer thickness (10 pct compression) Exit gap = Gap = 90 percent of veneer thickness (roller bar) Nosebal' compression angle = 15° (fixed bar) The lead of the fixed pressure bar ahead of the knife edge can be 0.03 inch (0.75 mm) for both the lathe and the slicer. The gap from the edge of the pressure bar to the plane of the ground face of the knife can be 90 percent of the thickness of the veneer being cut. Veneer 11;12 to lIf inch (0.8 to 6.3 mm) in thickness and of various species can be cut with these fixed pressure bar settings (fig. 24) . Generalized Setting 01 Roller Pressure Bar The generalized settings for lathes with a roller pressure bar are for cutting veneer ','tn to 1,4 inch (1.6 to 6.3 mm) in thickness. The lead of the roller bar should be 0.085 inch (2.16 mm). That is, the center of the 5.8-inch- (15.9 mm) diameter roller bar should lead the knife edge by 0.085 inch (2.16 mm). The comparable figure for the fixed bar is 0.030 inch (0.75 mm) (fig. 24 and tables 8 and 10) . An Alternate Generalized Setting 01 Roller Pressure Bar Collett, Brackley, and Cumming (6) describe setting a roller bar with the gap and exit gap equal. As with the rigid bar, a generalized set­ ting would be to have the gap and exit gap both 90 percent of the thickness of the veneer being cut (fig. 24 and table 11) . Generalized Setting 01 the Gap by Pressure Feihl and Carroll (12) report that pine veneer that is l~n to % inch (2.5 to 4.2 mm) in thickness can be cut satisfactorily with the pressure on a floating roller bar of about 60 pounds per linear inch (1.070 kg/m) of bar contacting the wood bolt. They further con­ clude: "It is not impossible that in some mills (when all species are fairly similar and veneer thicknesses are in the same range) it would be prac .. aI to use one pressure setting." Summary 01 Generalized Lathe and Slicer Settings Suggested "universal" lathe and slicer set­ tings-listed in figure 24-are not optimum settings, but they should permit cutting veneer of moderate quality from any species into any thickness from %2 to 1,+ inch (0.8 to 6.3 mm). (The roller bar is not satisfactory for use when cutting veneer thinner than l'Jn in. (1.6 mm).) In general, excluding the extreme ranges of specific gravity, one species of wood acts much like another and the veneer cutting process does not change abruptly \dthin the range of thickness from lr.l~ to I; inch (0.8 to 6.3 mm). The settings listed \\·ith figure 211 will gen­ erally result in a moderately tight cut. If tighter and smoother veneer is desired, smaller open­ ings between the knife and pressure bar may be used. Lathes having automatic pitch adjust­ ment could be set to have a knife angle of 91 0 at a bolt diameter of 36 inches (91 cm) and a knife angle of 89 0 30' at a bolt diameter of 6 inches (15 cm). Ideally, the rate of change of the knife pitch should be greater at the smaller diameters. A smaller fixed pressnre bar lead such as 0.020 or 0.01i) inch (0.5 to 0.4 mm) can be used for cutting ''tn-inch (1.6 mm) and thin­ ner veneer. Positioning Bolts and Flitches For maximum yield of rotary veneer, it is essential that bolts be chucked in the geometric center. If th..' bolts are chucked eccentrically as little as 1,,! inch, the recovery of veneer can be reduced significantly. H. C. Mason, an industry consultant, stated in 1972 that use of bolt­ diameter-measuring instruments and a mini­ computer controlling a lathe charger to pre­ cisely center the bolt in the chucks, will result in at least a 7-percent increase in recovery of veneer for a typkaJ Douglas-fir veneer plant. The way a flitch is mounted on the slicer table has little effect on yielcl, but it can affect the smoothness of the veneer (39). An eccentric flat-cut flitch should be dogged with the pith toward the start of the knife cut. A quartered flitch should be turned 180 0 when the cut ap­ proaches the true quarter. These and related phenomena are discussed in detail in (39). 68 CONVEYING AND CLIPPING VENEER A German machinery manufacturer l'ecently announced a system to reel sliced veneer by first applying string to the ends of the veneer sheets as they come from the slicer. The string then "leads" the veneer onto the reel where it can then be stored before unreeling into a dryer. Conveying Veneer from Lathe As veneer comes from the lathe, it may be manually pulled out on a table, but more gen­ erally it is moved to long trays in line with the clippers or is reelec1. The tray system is most common in both softwood and hardwood plants. As the veneer comes from the lathe, a short tipple directs un­ usable veneer to a waste conveyor. Usable veneer is directed into one of the trays with belts synchronized to the lathe speed. After one tray is full, the veneer is broken or cut, and the veneer directed to another tray. This must be done carefully to prevent the veneer ribbon from being folded and split. The second mechanical means of conveying veneer from the lathe is with a reel. The reel system works best with lx-inch (3.2 mm) and thinner hardwods cut from sound bolts. Like the tray system, the first unusable veneer is directed to a waste conveyor. Then the usable roundup is collected on a short tray or table. Finally, when a sound ribbon veneer comes from the lathe, it is tacked to a reel and the veneer reeled up as it is peeled. The speed of the reel is synchronized ,vith the lathe. The veneer is reeled with the loose side out. Combination tray and reeling is popular with some plants peeling species like lauan. The bet­ ter grades are cut into thin face stock and reeled. Lower grades are cut into thicker core stock and conveyed on trays. Conveying Veneer from Slicer I t is important to keep the sliced veneer sheets in consecutive order. In many plants, two men turn the veneer over as the sheets come from the slicer and stack them consecutively with the loose side up. In some cases, a short conveyor takes the veneer from the slicer to a position where it is more convenient to stack it. Some European plants automatically convey the sliced veneer to a veneer dryer. Dryer capacity should be sized for the ,yood veneer species, thickness, and production rate of the slicer. Clipping Green Veneer Veneer stored on trays is fed to one or more clippers. In a typical installation, with six trays from a lathe, three trays would feed to one clip­ per and the other three to a second clipper. A modern clipper has some sensing and measuring device so veneer can be clipped to nominal 4-foot (1.2 m), 2-foot (0.6 m), or random widths. Random widths may be generated when defects such as knots and splits are clipped from the veneer ribbon. An acclU'ate sensing device coupled with the clipper soon pays for itself by greater yields of usable veneer. The green veneer is then sorted by widths, grades, and possibly by sapwood and heartwood in preparation for drying. Reeled veneer is stored in racks and unreeled just ahead of the clipper. The clipping opera­ tion is much the same as that described for veneer stored on trays. One limitation of reeled veneer is that, if it is cut from hot bolts, it should be clipped before the veneer cools and sets in a curved shape. Flitches of green sliced veneer sometimes have defects clipped out or are trimmed before drying. Packs about Ii-inch (6.3 mm) deep are clipped together as a book. The green cUpping saves drying of material that will not be used. Clipping Dry Vcneer Veneer on trays or on reels is sometimes fed to the dryer in a continuous ribbon. As the veneer comes from the dryer, it is clipped to size. This system reportedly results in less waste and split veneer. One dryer manufac­ turer states that ch-ying of a continuous ribbon will result in at least a 4-percent increase in recovery of c11·y veneer. 69 VENEER DRYING An essential part of the veneer-producing process is to dry the veneer. The amount of this drying varies widely. Products that require a minimum of dryi.ng-such as bushel baskets and fruit containers-may bring the veneer be­ low a moisture content at which it will mold (about 20 pct). On the upper extreme is drying of softwood veneers that are to be glued with a phenolic hot-press glue, in which case the veneer must be 5 percent or lower in moisture content. In between are such products as deco­ rative face veneer, generally dried to 8 to 10 percent moisture content, and commercial hard­ wood veneers that are to be glued with a urea glue, in which case 6 to 8 percent moisture con­ tent is desirable in the veneer. In all cases, a major criterion is to dry the veneer at the lowest total cost. Because most veneer operations are set up in a straight-line production system and the pro­ duction from the lathe and slicer is very high, it is generally necesary to have a fast drying system. Dried veneer should: (1) Have a uni­ form moisture content; (2) be dried without buckle or end waviness; (3) be free of splits; (4) be in good condition for gluing; (5) have a desirable color; (6) have a minimum of shrinkage; (7) avoid collapse and honeycomb; and (8) have a minimum of casehardening. (Veneer is casehardened when the oute:!.· layers are in compression and the center or core is in tension.) Some Veneer Properties That Affect Drying Factors that affect drying of veneer include both the wood itself and the drying conditions. An obvious factor is the thickness of the veneer. Thicker veneers dry more slowly than thin veneers. A modification of this is variation in veneer thickness from the nominal thickness. Commercial %-inch (3.2 mm) veneer will often vary ±0.008 inch (0.2 mm) or more in thick­ ness. The thicker portions of the veneer take longer to dry than the thinner portions and COll­ tribute to a nonuniform fina1 moisture content. A second factor is the grain direction on the surface of the veneer. End grain dries several times faster than tangential (flat) grain. End­ grain drying is significant at the ends of all veneer sheets, which tend to dry faster than the bulk of the sheet. It may also be a factor in curly-grained or other figured veneer \"here at least partial end grain is exposed on the broad surface of the veneer. As these areas dry faster than surrounding straight-grain areas, they can cause stresses and buckling in the veneer sheet. The difference in drying rates between radial and tangential surfaces is small but may show up. Quarter-shred veneer will take slightly longet· to dry than rotary-cut veneer of the sanle thickness, and flat-sliced veneer may dry slower on the near-quarter edges than in the flat-grain area at the center of the sheet. The moisture in the veneer naturally affects the total drying time, as expressed in several ways. Veneer from butt logs may have higher moisture content than top logs. For example, the difference in moisture content of the heart­ wood of redwood from different logs may be as much as 2 to 1. Furthermore, the wetter heart­ \\rood veneer requires significantly longer dry­ ing time than drier heartwood of the same species. Comstock (8) indicates that density of the veneer may be another factor in total drying time. The denser wood heats more slowly than less dense wood and requires more total calories to heat and dry. The differences between the sapwood and heartwood may be factors with some species and not with others. Bethel and Hader (3) report that the sapwood of sweetgum will dry 25 to 30 percent faster than the heartwood of s\veetgum. The difference is attributed to the difference in permeability of the sapwood and the heartwood. This same phenomenon has been observed at the U.S. Forest Products Laboratory when drying veneer of tupelo and other hardwoods like over­ cup oak. In contrast, Comstock (8) reports that drying time in a .i et dryer does not depend on whether the veneer is heartwood or sapwood. Similarly, there is a lack of agreement on the effect of species on veneer drying. Fleischer (18) found that redwood and sweetgum heart­ wood dried at a slower rate than yellow-poplar heartwood. Bethel and Hader (3) also found differences in the drying of different species. Comstock (8) and Fleischer (18) indicate that veneer drying is controlled to a large extent by 70 the rate of heat transfer to the veneer. Fleischer qualifies this by saying that this controlling factor is a function of veneer thickne'"c:; and also to some degree of veneer species. Comstock (8) states that differences between species and be­ tween hardwood and sapwood are not important independent variables aside from their effect on the veneer density and moisture content. He developed a general equation for the time re­ quired to dry veneer in a jet dryer. He was, therefore, interested in generalities that could be used for any given species. Bethel and Hadel' (1) concluded that the drying rate of veneer may be controlled by moisture diffusion. From the literature then, it appears that the rate of heat transfer to veneer is an important factor in the rate of veneer drying. However, diffusion, at least in part, controls rate of dry­ ing in 1 ~-inch (3.2 mm) and thicker veneer of the impermeable species such as sweetgum heartwood. Reaction wood-tension "rood in hardwoods and compression wood in softwoods-shrinks more longitudinally than typical wood of the the same species. As a result, sheets of veneer containing streaks of tension wood or compres­ sion wood tend to buckle during drying. Do breaks (knife checks) in the veneer dur­ ing cutting have any effect on drying? Experi­ ments at the Forest Produ,..ts Laboratory do not show any difference in the drying rate of 1 Hi­ or 1;'-inch (1.6 or 3.2 mm) loosely cut and tightly cut sapwood veneer of sweetgum and yellow birch dried at ~WOo to 350 0 F (93 0 to 177 0 C) with an air velocity of SOO feet (180 m) per minute. The loosely cut veneer 'was easier to flatten after drying. SOlllP Dryel' COllditiollH That Can Alfeet Vf'IH"f'r Drvin" • r'I In general, dryers are operated to hold the veneer flat and transfer as much heat as pos­ sible to the veneer during drying. The importance of holc1ing the veneer flat can be judged by comparing matched sheets of veneer dried with various amounts of restraint. In general, buckle will be greatest in the veneer hung from the ends and allowed to dry at ambient room conditions. Next wi]] be veneer restrained by stickers and dried in a kiln. Veneer dried in a mechanical dryer with a roller or wire-mesh conveyor will buckle less than matched material dried in kiln. The least buckled will be veneer dried between flat hot­ plates. Temperature and drying time are factors that can affect the rate of drying. For example, 1 ~-inch (3.2 mm) heartwood of Douglas-fir dried at 250 0 F (121 0 C) may require 20 minutes in the dryer. The same kind of veneer dried at 320 0 F (160 0 C) may dry in 10 minutes. In­ creasing the drying temperature to 400 0 F (204 0 C) may reduce this drying time to about 6 minutes. Douglas-fir heartwood veneer has been dried in 2_1/.~ minutes by using a drying temperature of 550 0 F (288 0 C). Such a hig-h drying temperature may, however, lead J~.) i:Jl'ot'­ lems in gluing the veneer. Another factor which is universally agreed to affect the drying rate is the air velocity across the veneer surface. In 10ft drying, air move­ ment is very slow from convection currents. Veneer dried in a kiln might be subject to air velocities of several hundred feet per minute. This higher air velocity, together with the higher temperatures used in the kiln, greatly accelerates the drying. Prior to 1960, most mechanical veneer dryers had air circulation either in the longitudinal direction of the dryer or across the ,yidth of the dryer. Typical air velocities in such dryers were about 600 feet (180 m) per minute. Most me­ chanical dryers made after 1960 have the air impinging directly onto the face of the veneer through slots or orifices. The ail' velocity is in the range of 2,000 to 10,000 feet (600 to 3,000 m) per minute. This very high ail' velocity tends to break up any boundary layer at the veneer surface and greatly improves heat transfer. As a result, with a given dryer temperature, thin veneer will dry about one-third faster in a jet dryer than in a mechanical dryer having longi­ tu(linal or cross circulation air movement. The fastest heat transfer is by conduction. In general, with a given dryer temperature, veneer dried betweel1 heated platens requires less dry­ ing time than veneers in a dryer that depends On air circulation to transfer the heat. The dry­ ing occurs fastest when the metal cauls are per­ forated to allow moisture to escape while main­ taining high heat transfer from the hot plates. The roller conveyor or wire-mesh conveyor in conventional mechanical veneer dryer aids in the drying by transferring heat by conduction 71 to the veneer surface. Some investigators have reported that the heat hansfer from the rolls may be as much as 20 percent of the total heat transferred to the veneer. This heat transfer from the rolls is very obvious when comparing the drying rates of veneer through an essentially empty dryer and one in which the conveyor is full of veneer. In the full dryer, the rolls are cooled by the wet veneer and the required drying time for a given final moisture content increases. This means the first veneel' through an empty dryer will emerge much drier than veneer coming from a full dryer. If the drying time is set according to the first veneer through the dryer, the time '\vill be too short, and veneer coming from a full dryer will be much higher in moisture content. The relative humidity in a kiln can be used to control the final moisture content of the veneer. The relationship of wet-bulb and dry-bulb tem­ peratures to the final equilibrium moisture con­ tent of the "vood is shown in figure 25. The ability to control the final moisture content of the veneer is one of the main advantages of the dry kiln. Most veneer is dried in mechanical dryers at temperatures above 250 0 F. At these higher temperatures, Fleischer reports that l'elative humi(lity has no effect on the drying rate (18). As a matter of interest, the calculated equi­ libl'hlm moisture content of wood in saturated steam at 220 0 F (104 0 C) is about llvercent. At 240 0 F (116 0 C) it is about 5 percent. Re­ cent experiments show that veneer steamed at 220 0 to 240 0 F in a kiln or in a hot press will come to the desired final moisture content. Dry­ ing veneer to a controlled final moisture content should reduce degrade, reduce shrinkage, and provide a superior surface for gluing. Types of V {"nee-r Dryers By far the most common veneer dryer is the direct-fired 01' steam or hot water-heated pro­ gressive conveyor type. The roller conveyor is used most commonly with rotary-cut veneer. A wire-mesh conveyor is used for drying continu­ ous ribbons of rotary-cut veneer and for sliced and half-round veneer. It permits feeding the veneer sidewise so that the sheets can be kept in sequence for matching, in contrast to the roller dryer where the sheets are fed endwise. The 'wire-mesh conveyor is reported to work most satisfactorily with a restraint weight of about 5 pounds per square foot (24 kg/m2) when drying thin face veneer. In a roller dryer the roDers are generally hollow tubes which rest directly on the veneer. Both the roller con­ veyor and the wire-mesh conveyor can con­ hibute to drying by conducting heat directly to the surface of the veneer. Longitudinal, cross­ circulation, and impingement air movement are used in these progressive dryers. The method most commonly used in new veneer plants today is the jet dryer with the air impinging on the veneer surface at velocities of 2,000 to 10,000 feet (600 to 3,000 m) per minute. Some veneer is dried in progressive kilns. These kilns are operated at temperatures below 212 0 F (100'~ C) and, consequently, the relative humidity and equilibrium moisture content of the yeneer can be controlled. Control of the TInal moisture content and1)l'oductioll of veneer that is easily glued are two of the main advantages of the progressive kiln. Some products, like baskets, are assembled from green veneer and then dried. Usually heated tunnels with conveyors are used t~, dry veneer to about 20 percent moisture content to prevent mold. A few veneer plants llse progressive platen dryers. Many users of face veneer redry their veneer in a platen dryer. A rather unique face dryer made in Germany consists of perforated drums, with a partial vacuum inside the drums. The vacuum holds the veneer against the heated drum and re­ portedly 'works satisfactorily with relatively thin veneer. The dryer does not seem well adapted for veneer thicker than l~;;-inch (0.9 mm). An all-infrared dryer has been used com­ mercially on the "Vest Coast, but its use was discontinued because of high drying costs. Recently banks of gas-fired infrared heaters have been placed at the green end of a few dryers used . . v ith softwood veneer for construc­ tion plywood. They boost the temperature to reduce the drying time of thick sapwood veneer. Similarly, high-frequency and microwave en­ ergy have been used as a part of drying systems to equalize moisture content at the end of the drying cycle. These methods have not been gen­ erally used because of high equipment and power costs (59). 72 I /10 /80 /90 200 M 74591 F Figure 25.-Lines of constant equilibrium moisture content. 73 Drying veneer between peTiorated cauls in a hot press has been shown experimentally (30) to be a fast 'way to dry flat veneer. Veneer Drying Emissions A factor of current interest is veneer dryer emissions and whether they contribute to air pollution. Recent studies indicate the opacity of the plume from veneer dryers ranged up to 82 percent ,vith an average of 21 percent (1). Opacity is judged visually by qualified raters. Rating is in 20-percent increments similar to the Ringelmann Smoke Scale. The State of Oregon passed a law in 1972 limiting opacity of plumes from existing veneer dryers to 20 percent and from new dryers to 10 percent. The opacity of the plume can be reduced by using stack velocities over 2,000 feet (600 m) a minute. While this may pass the opacity limitation, it is costly because it results in a large heat loss. Also, it does not cut down on pollution. Another approach is to filter the stack gases at high velocity through a fiberglass mat. This system can reportedly reduce the average opac­ ity to 5 percent or less (5). Still another appro~,ch is to recirculate the air in direct-fired dryers through a heated duct at 1,200'; F. In one-half second the hydro­ carbons are incinerated and visibility of stack emissions reduced accordingly (5). Heat of combustion of the hydrocarbons is recovered by a heat exchanger to lower the total fuel needed to operate the system. Applied Drying Suggestions for Mechanical Dryers Dry the veneer as soon as practical after cut­ ting to minimize end splits, oxidation stain, mold, and blue stain. This is particularly im­ pOl·tant for light-colored wood. To minimize drying time, operate the dryer at the maximum temperature consistent with good glue bonds and wood color. In general, this will be about 400 0 F (204° C) at the green end and 360 0 F (182" C) at the dry end of the dryer. If gluing or \'eneer color are problems, lower the dryer temperature. Decreasing the dryer temperature by 100 0 F (38 0 C) (for ex­ ample, from 350 0 to 250 0 Ii' (177° to 121 0 C» will approximately double the drying time. Keep the dryer vents as nearly closed as practical. This will reduce the energy consumed and reduce veneer dryer emissions. If condensa­ tion and haze in the building become trouble­ some, open the vents the minimum amount needed to correct the problem. In general, operate the dryer with the maxi­ mum ail' circulation possible. It may sometimes be necessary to reduce the air velocity to pre­ vent overclrying and splitting of very thin veneer. Keep the dryer as full of veneer as possible. Dryer schedules should be based on a full dryer operating at a steady temperature and air movement. Segregate green \'eneer by required drying time. The green veneer sorts should be by veneer thickness, species, and-for many soft­ woods-by sapwood and heartwood. Doubling the yeneer thickness will more than double the drying time. Sapwood of species like Douglas­ fir requires about twice as much drying time as heartwood veneer. Heartwood and sapwood of many hardwoods dry in about the same time. Veneer containing both sapwood and hearh\Tood or wet streaks in the heartwood should be dried on the sapwood schedule. The veneer drying time should be regulated by the kind of veneer being fed in the green end. It is tempting for the dryer operator to change the drying time from the dry end, de­ pending on whether the emerging veneer seems too wet or too dry. If he does, there may be a constant shifting of drying times and a cor­ responding shifting in the average moisture content of the veneer out of the dryer. A better method is to carefully determine the proper time to dry veneer of a given thickness, species, and sapwood or heartwood and use this sched­ ule I"hen similar veneer is dried again. Even when the best dryer schedules are main­ tained, there will be a range of moisture con­ tent in the emerging veneer. Consequently, it is very desirable to have a constant electronic check of the moisture content in the veneer. Veneer having wet s pots can be pulled sepa­ rately. After standing overnight or longer, the veneer can be rechecked for high moisture con­ tent and wet pieces redried. If automatic moisture-detection equipment is not available, then the veneer out of the dryer should be checked regularly 'with a hand-oper­ 74 ated moisture meter. v\'hen such meters are calibrated for a given species and make firm contact on cool veneer, they are quite accurate froIT. about 6 to 15 percent moisture content. An eA-perienced dryer operator can some­ times tell in general the yeneer is drying by subjective methods. ViThen veneer is being over­ dried, static electricity makes the dryer snap and pop. Overdried veneer may be hotter to touch and in extreme cases may be darkened. Underdried veneer will be cool to touch, there 'will be less noise from static electricity, and the veneer may be more free of end waviness and buckle. All veneer should be cooled and held fiat as it comes from the dryer. Cool veneer is less likely to buckle and will not contribute to pre~ cure of gluelines. The dried veneer should be neatly stacked on fiat skids and the top of the pile weighted. Flitches of sliced veneer should be promptly strapped in fiat crates. QUALITY CONTROL browning of a freshly cut surface of an apple. Enzymes, moistul'e, favorable temperatures, and air are factors in this color change. Probably the best 'way to control this stain is to dry the veneer promptly after cutting so the surface is dried before oxidation takes place. Holding wet veneer over a weekend is likely to cause stain on susceptible wood species. Another control method is to heat the logs sufficiently to inactivate the enzymes present in the wood. This generally means heating the logs for 2 days at 160 0 F or higher rather than lim­ iting heating to .overnight. We have been told that running the veneer through boiling water as soon as it is cut may prevent the stain. \Vhen 'wet wood comes in contact "'itll iron or steel, it reacts to form a blue-black stain. The stain becomes worse the longer the contact and the hotter the wood. It may be particularly prevalent on woods like oak that have a high tannin content, and is very noticeable on light­ colored wood like the sapwood of maple. Such stain is not particularly important for uses like construction plywood but is very objectionable on decorative face \'eneer. Control methods include keeping the knife and pressure bar as clean as possible; heating the knife and pre::;sure bar to reduce condensa­ tion; lacquering the knife and pressure bar so that only the extreme edges have exposed steel that can stain the wood; using stainless metals for the pressure bar and knife; using a double be\'el on the slicer knife so the heel of the slicer l;::nife cannot rub against thefiitch; using a greater knife angle (more clearance) so the heel of the slicer knife does not contact the flitch; and using less nosebar pressure. Undried Veneer The quality of veneer is affected by log qual­ ity, by the care used in storing the logs or flitches, by heating the wood prior to cutting, and by the mechanical condition, setup, and opel'ation of the lathe or slicer. Quantitatively five factors should be checked at regular intervals: Stain, uniformity of thick­ ness, roughness of the veneer surface, breaks in the veneer, and buckle or other distortions of the veneer. Control of Stain Stain on veneer may be due to fungus, oxida­ tion, or contact of the wet wood with iron 01' steel. Blue stain is the most common fungus stain that occurs readily in the sapwood of most spe­ cies if unprotected logs are stored during: warm weather. The best control is rapid processing of the logs or storage of the logs under water or under a 'water spray. If water or 'water spray is not available, end coating the logs is bene­ ficial. Oxidation stain is generally a yenow or tan stain that may penetrate from the ends of un­ protected logs during summer storage. Uke fungus stain, it can be pl'evented by rapid proc­ essing of the logs or by storing logs uncleI' water 01' und<::'r a water spray. End coatings are also helpful. Oxidation stain may also occur on the surface of veneer sheets between the time they are cut and dried. A common example is the yellow stain that may develop on birch 01' maple sap­ wood. The stain is 80metimes compared to the 75 ,., (OIllr,d of 1 ('J/('(', Thicl"Il',\,\ , L: , . flf·! I ~ ~l~ ,I, I J' H ..' . ~. !) . t ~ ~~ . ! 1 r' t· : l~ I !l,r' : " " i I .; ;\" ' ·r· ,.,' f>!' I , , ," 'tIP"~: f, :~ I ~ I f-1,! f'f'l' t: . k 'd~' . 1 . 'Ii ,: ,.', ! r (i, at .' 1 I( :4' '" " :, , " ,1 , 'I- ~ " : , ;" , jf' , ;, 1 :p,~, p~ ,;, t' ,t , ' I' . , ,p, '. I . ,~ ,,~ . 1, ! ! p r,' , )t'P. : I I·~,,j' ·i1;:t:tt .• ' !j4}"OI PUl'lH-:--.p .. , Tt '<'. Hu:d Jlrn~l~ :d,,\ ~j:t,\ til f·a'.p .t (·(lnl1Iltr~.ttd :-.~1!~· a .... qp .. -!'! ,!H·d .\ I~r~"a!~t. }lptpt'". unt! lI(,p!,~ipr « ; ) j'f ' .. , . ,~ ! ~ . , 1 'h Tl ... ! .' .. H1;\ il 'I' f'll!da('tmg -uI'Lw" I ~,7 llllll) Ili dialrlPtp), :,' 'I ~ ~ j , ' Pi!..-,·r t lIt; ihp ("1' ;It'\ 1: al,ollt ".I;(i :,',:1'.; 1:;1111 :.'), \\'r:!'I:, ('!lI·,idli.!!' jhidHfP'~ ,,( '1':,'" \P!!t'f'I', \\P t,;t\p 1'''l1lld at! pr '.\ iL (·tid u ....,tt. 1:'11" PX;tft:l;g Jlprlpd!pd iif~ 1t,p ;tt f~.~H l!l;t\' l.p a ;.nlHll<: ~,: ~ 'Pl" \\' j!l tI{lcod t, , f 'f' 111 "('1'\ cHid . . . p1 ilJ • alld , 'l·f·ra'l'd \\'j! h I Veneer Thickness 1..j l'R 11.(; )~2 1,tH (In.) (0.250) ( .125) ( .0(2) ( .031) ( .016) (mm) 6.3 3.2 1.6 .8 A Tolerance (in.) ±O.OO ±.004 ±.003 ±.002 ±.OOl (mm) ±O.127 ±.102 ±.O76 ±.051 ±.025 care to produce veneer that will consistently meet these specifications. Many commercial operations run with tolerances approximately double those listed. Control of Thickness of Veneer Cut on Lathe The most common fault in veneer thickness is thin veneer for the first few revolutions of veneer cut on the lathe. The major cause of this thin veneer is looseness in the moving parts of the lathe. A secondary cause is deflection of the \yood by the pressure bar beyond the knife edge (29). Further, when the knife alone is contact­ ing the wood, the knife carriage and the wood work piece are pulled together. In conh'ast, when the pressure bar is contacting the wood, the knife carriage and the wood work piece are forced apart. To minimize the production of thin veneer at the start of cutting, the lathe should have tight-fitting parts; the preSSUl'e bar should be closed from the start of cutting and throughout the cutting; and moderate nosebar pressure should be used. This is discussed in more detail by Lutz, Mergen, and Panzer (.H). Another cause of variable veneer thickness is an improper setting of the knife angle or knife pitch. If the pitch is too low, the veneer is thick and thin in waves, the CTest of which may be 1 or more feet apart. FeihJ and Godin (16) report, "This defect is particularly pronounced in winter 'when veneel' is cut from logs that are not adequately heated and contain some frozen wood, When such logs are peeled with a low knife angle, the frozen parts tend to produce thin veneer and the thawed parts thick veneer." The corrective measures are to heat the logs to a uniform temperature and to change to a higher knife angle (greater clearance angle). 111 139 941 Figure 27.-An air-operated device for measuring veneer thickness. Tbe preSSUl'e on the anvils can be easily changed to suit the species and thickness being measured. 77 A number of investigators (4) have found that wood having high moisture content is more susceptible than drier wood to being cut thinner thc:.n the knife feed. An example is the tendency of Douglas-fir sapwood veneer to be thinner than heartwood veneer vvhen cut with the same lathe settings. One solution is to use less nose­ bar pressure when cutting sapwood of conifers than when cutting heartwood. Wood having high moisture content, such as southern pine sapwood, tends to be thinner than would be expected from the knife feed 'when cut at fast speed and with high nosebar pres­ sure (43). Slower cutting speed or less nosebar pressure should result in better thickness control. Shake, heart checks, or splits in the log,s.nd soft centers that allow the bolt to move in the chucks can cause irregular veneer thickness. These unwanted thickness variations are re­ lated to specific bolts and do not occur on sound bolts. Larger chucks and continuous end pres­ sure help when cutting bolts with soft centers or with large end splits. Misalinement of the pressure bar and knife may cause a thickness variation from one end to the other end of the veneer sheet. If the bar moves back at one end of the lathe, the gap or horizontal openin~: is wedge-shaped. As a result, the emerging sheet of veneer is thick and short at the edge cut with the large gap, and thin and long at the edge cut at the smaner gap. The veneer coming from the lathe runs in the direc­ tion of the thicker veneer and the bolt takes a conical shape. The corrective measure is to aline the bar parallel to the knife. Then check for play in the nosebar assembly. Movement of the pl'essure bar during cutting may be greater at one end than the other and so cause misaline­ ment (16). Misalinement of the lead of the pressure bar with respect to the knife may also cause this phenomenon but it is less likely to ,iccur and relatively less important than misalinement of the gap. A conical-shaped bolt may also be caused by a much larger overhang of one spindle than the other. The remedy is to center the bolt endwise with respectto the knife. Similarly, if the knife edge is not parallel to the axis of the spindle, a conical bolt win be generated. The correction is to adjust the nut of one of the feed screws of the lathe carriage until the knife frame is parallel to the axis of the spindles (15). Misalinement of the knife and bar may cause barrel-shaped bolts and veneer that is thicker at the edges than in the middle. This may be caused by closing of the bar lead and gap at the center of the lathe due to heat expansion when cutting hot bolts. It can best be corrected by heating the knife and bar prior to setting up the lathe. Alternately, the lathe can be equipped with a cooling system or the nosebar frame may have a yoke and pull screw. A barrel-shaped bolt may also be caused by bending of the bolt in the lathe. This is most likely to occur when cutting long bolts to a small diameter. Use of a backup 1'011 can pre­ vent bending of the bolt during peeling. Control of Thickness of Veneer Cut on the Slicer The pressure bar is generally bolted into posi­ tion on the slicer and the flitch is backed up with a steel table. Consequently, the veneer cut on the slicer may be more uniform in thickness than veneer cut on the lathe. Since most veneer cut on a Elicer is t'tH-inch (1.6 mm) or thinner, this also makes thickness control less of a prob­ lem than 'with thicker rotary-cut veneer. Even so, the first few sheets cut on a slicer may be thinner than nominal thickness. The cause is primarily play in the feed mechanism and the flitch table. As with the lathe, it may also be due to compression of the wood beyond the knife edge by the pressure bar (29). A warped flitch that is not held securely against the flitch table by the dogs may also result in thin veneer. Having all slicer parts closefitting, the flitch securely held against the flitch table, and using moderate nosebar pressure should minimize these sources of nonuniform sliced veneer. Less common reasons for nonuniform veneer include heat distortion of the knife and pressure bar that results in veneer cut from near the center of the slicer to be thin. Heating the knife and pressure bar prior to setting up the slicer is the best way to overcome this problem. Yokes and pull screws on the pressure bar holder can also be used to help correct the alinement of the pressure bar to the knife edge. A non uniformly heated flitch may also result in nonuniform veneer thickness. 78 M 141 666 Figure 28.-An instrument for measuring roughness of wood surfaces by moving a stylus across the rough sur­ face. The insert shows the type of trace the instrument records. A slicer that indexes the previously cut sur­ face against a stop plate may produce uneven veneer if splinters or other debris come between the flitch and the stop plate. Slicers having a pawl and ratchet feed must have the same number of teeth advanced every stroke. If the mechanism is not set carefu ny, an incoTrect thickness may be produced. Simi­ larly, if the feed index train is not braked, momentum may carry the knife carriage beyond the desired index. Splits or shake in flitcheli can cause uneven veneer thickness. These thickness variations do not OCcur with sound flitches. Control of Veneer Roughness Like nonuniform veneer thickness, veneer roughness is undesirable for all end uses. Rough veneer can cause gluing problems, require ex­ cessive sanding, and cause finishing problems. Measuring the roughness of wood surfaces is a complex problem. Peters and Mergen (54) described (\ stylus trace method they developed for measuring wood surfaces (fig. 28). Earlier Lutz (38) described a light-sectioning method for measuring roughness of rotary-cut veneer (fig. 29). Northcott and Walser (50) have pub­ lished a visual veneer roughness scale which in turn was obtained by measuring depressions on the surface of the veneer samples with a dial micrometer. For research, the stylus trace method, the light-sectioning method, and the dial micrometer give values fOr comparative purposes. For mill use, a visual veneer rough­ ness scale is probably more useful. Actual veneer samples that have been measured for 79 surface roughness in the laboratory could be kept near the lathe or slicer for visual com­ parison with the veneer being produced. The orientation of the wood structure (39) and the growth rate of softwood trees (40) affect the smoothness of knife-cut veneers. When cutting against the grain of the wood fibers, annual rings, or wood rays, the wood tends to split ahead of the knife and into the wood work piece, causing depressions on the tight side of the veneer. The annual ring effect is most pronounced when rotary-cutting fast­ grown softwoods at small COTe diameters. The ray effect is pronounced when quarter-slicing goes beyond the true quarter. Cutting against the fibers occurs around knots, with curly grain and with interlocked grain. The thicker the veneer, the more likely the veneer will be rough. It is sometimes possible to mount the flitch or bolt to minimize cutting against the grain (39). Probably the best control is to adjust the nose­ bar to increase the pressure just ahead of the knife tip and so reduce splitting ahead of the knife. Proper heating of the wood and use of a sharp knife also help reduce this roughness. Another type of roughness is a fuzzy surface. It is most common on low-density hardwoods like cottonwood that contain tension wood. Over­ heating of any species may also cause fuzzy sur­ faces. Oontrol may include log selection to avoid tension wood, cutting the wood at as Iowa tem­ perature as is practical, and keeping the knife sharp. An extra hard knife will keep a sharp edge longer than a soft knife and can be used 'with low-density woods. Use of a slightly eased fixed nosebar edge and continuous flushing of the surface between the wood and the nosebar with cold water may also help. M 141 667 Figure 29.-An instrument for measuring veneer surfaces by light sectioning. The insert shows what i,~ seen through the magnifying glass of the instrument. 80 Shelling or separation of the springwood from the summerwood may occur when rotary­ cutting or flD.t-slicing both softwoods and hard­ woods that have a relatively weak zone between the springwood and summerwood. Hemlock, true firs, western redcedar, and angelique are species that may develop shelling. Overheating of the wood, too much nosebar pressure, too sharp a nosebar, or a dull knife may contribute to shelling. Shattering of the veneer surface is somewhat like shelling and may occur v{ith wood having a high moisture content and low permeability. For example, Douglas-fir sapwood and sinker redwood bolts may develop shattered veneer surfaces if cut at high speed and with high nosebar pressure. Apparently water in the wood is compressed so fast that it ruptures the wood structure to escape. LO'wer nosebar pressure and slower cutting speed reduce the occurrence of shattered veneer surfaces. Nicks on the knife edge or pressUl'e-bar edge may cause scratches on the veneer. Scratches from the knife occur on both the tight and loose side of the veneer while scratches from the pres­ sure bar occur only on the tight side of the veneer. These scratch marks are so common that they can often be used to distinguish one­ half-round from flat-sliced veneer. The scratches on the half-round veneer are at a right angle to the length of the sheet while those on flat-sliced veneer are at some acute angle corresponding to the draw of the slicer. Careful examination of the veneer, followed by honing the knife and pressure bar when necessary, will minimize these scratch marks. This is particularly im­ portant for decorative face veneer. The scratches may take more stain than surrounding wood even if the sanded wood appears to be free of scratches. Grain raising is occasionally seen on soft­ wood veneer cut from wood having a dense summerwood and much less (lense springwood. Excessive pressure from the nosebal' overcom­ presses the springwood. After the veneer is cut, the springwood recovers, resulting in raised grain. The cor:rective measure is to reduce the nosebar pressure. Feihl and Godin (16) report that bulging of knots in the core is related to raised grain and they suggest increasing the knife angle as ",:ell as decreasing the nosebar pressure as means of correcting this fault. 81 Corrugated veneer with three or four waves pel' inch of veneer is generally associated 'with too high a knife angle. Feihl and Godin (16) report corrugated veneer can also be caused by cold or dry wood and by setting the knife edge too low. Other causes are too much overhang on the spindles, cutting to a sman core without adequate support for the core, and wood bolts that become loose in the chucks. Corrective measures are obvious from the stated causes. Cont,.ol of Cracks 0,. B,.ea.ks into the Venee,. Breaks into the veneer may be on the side of the veneer that is next to the knife or on the side next to the pressure bar during cutting. By far the most common are small cracks that de­ velop on the side of the veneer next to the knife. They may be caused by splitting ahead of the knife edge or by bending the veneer as it passes the knife after it is cut. The terms tight and loose side of the veneer refer to this phenom­ enon, with the loose side being the side that has the checks. These small breaks are also known as knife checks, lathe checks, or slicer checks. Less prevalent but perhaps more serious are breaks on the bar side 01' tight side of the veneer. Three samples are grain separation, lifted grain, and cracks approximately perpen­ dicular to the veneer surface. Loosely cut veneer is weak in tension perpen­ dicular to the grain. As a result, it may develop splits or break readily dming handling, thus lowering the grade of the veneer. Deep checks in face veneer may also contribute to surface checks in furnitme or other finished panels. On the other hand, loosely cut veneer may develop more wood failure than tightly cut veneer. As a result, veneer is sometimes cut loosely on pur­ pose to increase the wood failure when the plywood is evaluated by the standard plywood shear test. Three methods have been used to measure looseness of veneer. One method is to pull l-inch- (2.54 cm) long veneer samples apart in tension perpendicular to the grain on a suitable test machine (fig. 30). Because of variability, a minimum of about 30 samples should be tested to obtain a value for a given cutting condition. The values obtained can be compared with values for matched sawn and planed pieces of the same size. A second method of evaluating veneer checks is to apply an alcohol-soluble dye to the checks by brushing it on the dry veneer surfaces or by dipping the end of the dry veneer in the dye. The dye penetrates into the checks. The depth of checks as a percentage of the veneer thick­ ness can be estimated from scarfed sections of the samples (fig. 31). The method works very well with relatively impermeable veneer such as Douglas-fir heartwood where the dye is gen­ erally confined to the checks; it is less satisfac­ tory with permeable veneer such as southern pine sapwood due to overall penetration of the dye into the wood. A third method is to flex the veneer across the grain. Tightly cut veneer is stiffer than loosely cut veneer. Two factors are most important in minimiz­ ing depth of checks on the loose side of the veneer. They are adequate heating of the wood and use of adequate nosebar pressure. Factors that may increase checking are logs that have partially dried and use of a knife bevel much greater than is commonly used. + + / - 1" ~ \ J M 108 074 Figure 30.-A veneer specimen in the grips of a ten­ sion testing machine. Assuming proper heating schedules are bdng used as described earlier, the temperature through the flitch or bolts should be relatively uniform. One way to check the bolt temperature is to drill a Ii-inch- (6.3 mm diameter hole radially an inch or two (2.5 to 5 cm) deep at the center of the cores remaining arter cutting veneer from Im·ge- and sman-diameter bolts. A thermometer should immediately be inserted in the hole and the temperature recorded. This temperature should be 'within 10° F (5° C) of the desired temperature for good cutting. This method is recommended over measuring the temperature at the surface of the bolt, as the surface temperature of a heated block changes very fast when it is exposed to air. If the measmed temperature is not satisfac­ tory, the heating schedules should be rechecked and the actual temperatures in various posi­ tions in the heating vat should be monitored with thermocouples throughout the heating cycle. N osebar pressure was described ill detail earlier. For quality control, perhaps the most useful procedure is to be certain that the lathe or slicer settings are made with instruments, and that gages are mounted on the equipment to show any unwanted movement of the nosebar with respect to the knife edge during cutting. With good veneer species like yellow birch and yellow-poplar, it is possible to cut veneer as thick as ~B-inch (3.2 mm) with no visible checks on the knife side of the veneer. Grain separation is similar to shelling and is a failure of wood between annual rings. The defect may not be noticed in the green veneer but later causes trouble when the plywood made from the veneer is bent as for a boat hull. Two species that have developed the defect are okoume and lauan. The cause is related to rela­ tively weak zones in the wood and is generally considered to be due to setting the bar with too much lead and too small a gap. If suspected, it may be detected in dry veneer or plywood by tapping with a coin or stroking with a stiff brush. The void causes a different noise than the noise that comes when tapping or brushing sound veneer. Lifted grain is a separation of large groups of fibers in figured veneer like curly birch (16). It is serious because such areas cannot be 82 Figure :n.-A 1\1 107 770 ~('arf"d »ampi" of hiJ'f'h ,'PI1PPI' to "how chp('k" about OI1P-thil'd of tllP thicknNl~ of thE' \"('nppl'. A dye \Va" appli"d prillI' to "eu1'flng to makp thl' ehi'ck" stand out. sanded to a smooth surfacl:!. Careful setting of the knife and pressure bar ma~' minimize this defect in thin face veneer :-;uch ag l:!l-inch (1 mm), Extreme curly grain :-;hould not be cut into thicker veneer if lifted grain is to be avoided. The last type of cracks to he discussed in­ volves breaks perpendicular to the tight side. They may occur if excessiye nosebar pressure is used. or if the nosebar lead puts excessive restraint on the venc,_J' as it passes between the knife and the pressure bar, Breaks on the tight side of the veneer can be detected by the ten­ sion test and by the alcohol-soluble d~'e test the same as breaks into the ioose !-iide of the veneer. Careful setting of the pressure bar will elimi­ nate thi:o; problem. Control of Bllcklt, in (;u'(>ll "(,ll('er Buckle i:-; unde:-;iJ'able ag it intel'fel'e~ with edge gluing, glue :o;pl'eariing, and panel layup. Vi/hen it is :-;evere it may emtse overlaps or splits in the pl~'w(J(J(1. BtH'kled venper e([used by l'eaetion wood ma~: abo cause "'m'ped panels in ser\'ice, Buckle, like end wu\'ines:-;. may he measUl'pd by deviation from a plane :-;uli'aee by pla('jug' the buckled veneer between two flat pm'allel 83 :o;urfaees and recording the spacing. Commonly, buckle i:o; rated visually as mild, moderate, 01' :-;evere. Buckle in green veneer may ill' caused by re­ action wood or b~' uneven pressure against the bolt or flitch during cutti ng. Compression wood in softwoods and tension wood in hal'dwooci:-; have different longitudinal :-;tresse:-; than normal wood. \\'hen sheets of veneer containing hoth reaction wood and normal wo:)d al'e cut, the veneer may buckle as it tome:-; from the lathe or slice]'. Drying accentuate:-; thi:o; buckle. Logs from species known to be ]ll'One to develop reaction wood :o;hould be examined prior to ('utting and not be ('ut into veneel' if the reaction wood is pro­ nounced. {'neyen pressure against the bolt. or ftit('h may he due to heat distortion of the knife and pl'e:O;:-;U!'e hal' :o;etting on the lathe or slicer; bow­ ing of small-diameter bolts on the lathe; jam­ ming of a ehip 01' splinter between the pressure bar and the bolt or flitch; or a tight spot due to a local deviation of the knife or pressure bar edge:-; from a straight line. As discussed erl"lier, heat diRtortion can be minimized by heating the knife and pressure bar prior to setting them. Bowing of the bolt may be minimized by reducing the nosebar pressure and by using a backup roll. Some lathe operators judge the correct nosebar pressure by whether the veneer buckles in the center of the sheet. If the center of the veneer ribbon is buckled, the pressure is too high and the nose­ bar gap is widened. A splinter or chip jammed between the knife and bar in effect puts very high local pressure on the wood and causes the veneer to be thin. A bump builds on the bolt 01' flitch. If it is pronounced, the veneer may develop a hole at this area and the knife may be bent. The cor­ rection is to stop cutting, open the pressure bar, remove the chip 01' splinter, close the bar, and resume cutting. Use of a roller Lar helps reduce this defect as the chips are more readily pushed past the opening between the knife and pressure bar. Setting a fixed bar with more lead may help reduce this problem. Having the bolt or flitches clear of bark and loose splinters is good practice and will reduce jamming of particles between the surface of the bolt or flitch and the pressure bar. Finally, if the knife and pressure bar are not ground straight, there may be a local tight spot that will result in buckled veneer. The correc­ tion is to grind the knife and bar straight. Both surfaces of the knife edge should be ex­ amined and if necessary both should be ground to straighten the edge (24). Dry Veneer Most veneer readily dries satisfactorily for the intended end use. But since veneer is easy to dry, potential problems are sometimes over­ looked. Some veneer drying problems are nonuni­ form moisture content in the veneer as it emerges from the dryer, buckle and end wavi­ ness of veneer sheets, splits and checks in the veneer, a veneer surface that is difficult to glue, scorched veneer surfaces, veneer that shows signs of collapse, honeycomb, or casehardening, exces::;ive veneer shrinkage, and undesirable color. Control of Final Moisture Content Probably the most universal problem in dry­ ing veneer in a progressive mechanical veneer­ type dryer operating above 220 0 F (104 0 C) is the nonuniform moisture content in the ve­ neer as it comes from the dryer. This is true of a dryer having longitudinal circulation, cross circulation, or jet impingement circulation. It is similarly true for a progressive platen-type dryer. For example, veneer dried to an average moisture content of 8 percent will generally have a range of moisture content from about 2 to 20 percent. This is because the equilibrium moisture conditions in the dryer are for all practical purposes 2 percent or less. When drying to an average moisture content of 8 per­ cent, the faster drying veneer may come to 2 percent and the slower drying to 20 percent moisture content. In other words, any differ­ ence in the drying rates of different areas of the same sheet of veneer then results in a ,vide range in final moisture content in the veneer as it comes from the dryer. To keep this problem to a minimum, the green veneer should be sorted for thickness, moisture content, and density. Better control \vill probably result if the green veneer is also sorted for sapwood and heartwood and by species. Assuming the veneer is being sorted as well as possible to have veneer of one type being dried at a time, the next point to check is the uniformity of drying conditions in (Ef­ ferent parts of the dryer. Modern veneer dryers are generally designed to have uniform temperature and air movement throughout the dryer. However, it may be worthwhile to check these factors. Is the tem­ perature at the top conveyor the same as it is at the Lottom conveyor? Is the airspeed ap­ proximately the same in all parts of the dryer? One method of checking this is to run matched samples of veneer through different portions of the dryer. For example, one sample can be run through the left side of the upper conveyor, another through the right side of the upper conveyor, another through the left side of a lower conveyor, and so on. Then carefully check these samples for moisture content immediately out of the dryer. If this test shows that one portion of the dryer is consistently drying ve­ neer faster than another, drying rates can sometimes be eqnalized by adding steam coils, baffles, or fans where needed in the dryer. Another way of controlling the final mois­ ture content is to dry all of the veneer to 5 per­ cent moisture content 01' less. This may result 84 in overdrying of some of the veneer, but it will l'esult in a llalTOWer range of veneer moisture. A very common method of reducing the spread of moisture in the veneer is to electron­ ically measure the moisture content in each piece of veneer as it comes from the dryer. Veneer that has a moisture content higher than the desired maximum is marked and pulled separately for further drying. Leaving this ,vet veneer in a solid stack overnight will help to equalize the moisture content. A re-sort through the moisture detector the next day will reduce the number of pieces that need to be reddec1. Some moisture meters are sensitive to wood temperature as well as moisture content. They should be calibrated under the conditions in 'which they will be used. Another method that is sometimes used when nonuniform moisture content is a serious prob­ lem is to dry in two stages. In the first pass, the veneer is brought to an average moisture content of about 20 percent. It is then stacked overnight to allow some equalization and rerun the next day to the average moisture content desired. High-frequency or microwave units have been used experimentally at the dry end of the dryer to equalize the moistJre content of the veneer. Both these methods work on the principle that the higher moisture areas in the yeneer absorb more energy. Heating and drying are propor­ tional to this absorption of energy. Both of these methods do equalize moisture content in the veneer, but they have not been generally adopted because of cost (li9). It is possible to dry veneer to controlled mois­ ture contents in superhea.ted steam at atmos­ pheric preSSUl't;> To date this method has not been used commercially. Control of BllCkl(~ Buckle in veneer may be caused by stresses in the wood, by reaction wood, by irregular grain with resulting irregular drying rates and irregular grain with resulting shrinkage, and possibly also by improper setting of the lathe or slicer. Use of the maximum restraint that will hold the veneer flat 'without causing it to split dne to shrinkage stresses will help to minimize buckle. Similarly, anything that can be done to dry the veneer to as uniform a mois­ ture content as possible will reduce buckling. In most cases, buckling can be minimized by redrying in a plate dryer. The redrying tem­ perature and time will depend on the moisture content of the veneer (.4.1). Control of Splits Splits in veneer that has been dried in a pro­ gressive mechanical dryer are generally related to splits that were in the green veneer or result from rough handling. If stacks of green veneer must be held before dlying, the ends should be protected from end drying by covering them with a plastic sheet (such as polyethylene) or if necessary by spraying them with water. A recent development for controlling han­ dling splits is green veneer taping. Tape is applied at the lathe primarily to veneer thinner than li!fi inch (1 mm). Taping reportedly im­ proves the veneer grade, and reduces the need to splice and repair veneer. Forest Products Laboratory experiments showed that 1 ~-inch­ (12.7 mm) 'wide flexible tape applied to the spurred ends of the green veneer reduces end waviness. Another method of reducing handling splits is to dry rotary-cut veneer in a continuous rib­ bon using a wire-mesh conveyor in a mechan­ ical dryer. The method was used as early as 1950 'with birch veneer which was reeled as it came from the lathe and then unreeled into the dryer. The dryer veneer was then clipped for grade. More recently a system has been developed where softwood veneer is stored on long trays and then fed in line to the dryer. In addition to reducing splits, recovery is reportedly im­ proved because the veneer is clipped dry and it is not necessary to oversize to compensate for variability in shrinkage. Control of Veneer Surfaces for Glll.ability Poor glue bonds have been reported with veneer dried in direct oil-fired dryers operating at temperatures as high as G50° F (288 C). This is less of a problem with direct gas-fired dryers and less yet with sLeam-heated dryers. Dropping the temperature to 400 0 F (208° C) or lower improved the gluability of the veneer. Causes of glue interference may be \yeakening of the surfaces and extractives brought to the wood surface during high-temperature drying. 0 85 At any rate, use of a lower drying temperature and prevention of overdrying the veneer are the common means of overcoming veneer glu­ ing problems. Control of Dryer Fires and Scorched Veneer High drying temperatures may cause scorched veneer and possibly fires in the dryer. At temperatures from 200 0 to 300 0 F (93 0 to 149 0 C), extraneous materials volatilize from wood. From 300 0 to 400 0 F (149° to 204 0 C), there is scorching and slow evolution of flam­ mable gases from the wood. This progressively 0 becomes more rapid until at about 600 0 to 650 (316 0 to 346 0 C) the wood can ignite spontane­ ously. Even if wood does not ignite spontaneously until the temperature at its surface reaches about 650 0 F (346 0 C), if the surface becomes charred, charcoal gases may ignite at a temper­ ature as low as 450 0 F (232 0 C). Extraneous materials such as turpentine also ignite at a temperature of about 450 0 F (232 0 C). Veneer being dried in dryers operating at 400 0 F (204 0 C) or less sometimes ignites in the dryer. These fires may be caused by a static spark that ignites flammable gases of volatile extraneous materials. Avoiding overdrying and use of controlled lower drying temperatures are the primary means of preventing dryer fires and scorched veneer. Control of Collapse, Honeycomb, and Casehardening Collapse and honeycomb may occur in species that are relatively nonporous. Typical examples would be %-inch (3.2 mm) and thicker heart­ wood of sweetgum and overcup oak. Collapse in s'weetgum heartwooc is likely to occur in early stages of the drying. Sweetgum dried at 350') F (177° C) had much more honeycomb than sweetgum heartwood dried at 150:' F (66:' C). Experiments at Madison showed that 1,~_ inch (3.2 mm) overcup oak dried at 320 0 F (160 0 C) might shrink as much as 20 percent in thickness. The solution to these drying prob­ lems in all cases appears to be to use a lower drying temperature. Casehardening was at a maximum in l~-inch (3.2 mm) heartwood of sweetgum when dried at temperatures of 120 0 to 160 0 F (49 0 to 71 0 C). Casehardening can be removed by use of high temperature, particularly if the veneer has a high moisture content. Control of Shrinkage Widthwise shrinlmge of flat-grain veneer generally decreases with increasing drying temperature. For example, ~';;-inch (3.2 mm) yellow-poplar dried at 150:) F {66 e C) shrank 6 percent; when dried at 250 c F (121 P C) jt 0 shrank 51~ percent; anel when dried at 350 F (177 C) it shrank 41~ percent. In contrast, the shrinkage in thickness tends to increase ivith an increase in (hying temperatul'e. 0 Cont.rol of Color Color in face veneer call often be controlled to some degree by varying the time that the green veneer is held in a stack prior to drying. In general, the wet veneer tends to oxidize and darken in storage. Consequently, if a light color is desired, as with the sapwood of hard maple, the veneer should be dried as quickly as possible after cutting. In other cases, it may be desirable to have some color change take place in the green veneer stack. An example is black walnut. The color of the sap\\'ood and heartwood changes gradually in the warm green stack. ViThen the desired color is reached. the veneer is sent through the veneer dryer. 86 VENEER YIELDS AND VOLL'ME NEEDED FOR A PLANT VENEEH YIELDS (ROTARY CUTTING) 'Vith knife-cut veneer one might assume that veneer recovery could equal the volume of the log minus the volume of the core. rnfortunately this is not the typical case. For example, durin?: peeling of Douglas-fir in commercial plants, ViToodfin (68) fonnd losses due to: spurring, 2 percent; roundup, 51~ percent; green end clip­ per loss, 22 vercent; below-grade veneer, G per­ cent; core, 91~ percent; and veneer shrinkage 3 percent. Thus the actual recovery of dry ve­ neer was onl:v G2 pen'ent of the total green block cubic volume. This is typical of yield studies in industrial plants. The losses at different stages vary with the quality and diameter of veneer blocks. Cylin­ drical logs have less loss from roundup than logs with pronounced taper or crook. Assuming the core diameter is constant, large-diameter logs ha\'e a smaller percentage loss as ('ore than small-diameter logs. Sharp increases in log cost~ in 1973 stim­ ulated interest in meHns of im]lroying veneer yields. Baldwin's book. "Plywood Manufactur­ ing Practices" (,2), describes good ind ustry practice in 1975 to maximize recovery of ve­ neer. Some techniques described include backup rolls and retractable chucks to aid cutting to smaller cores, use of a moving knife to separate the veneer ribbon going to different trays, veneer clippers having devices to sense open defects and clip automatically for maximum yield, and veneer 5heet composers. A technique for increasing yield that has been described (2.3) but not adapted is to pre­ cisely measure block diameters, feed the in­ formation to a computer which in turn directs the charging device to precisely chuck the block in the geometric center. Estimated incre::tsed yields Hre up to 7 to 8 percent. Drying veneer in a ribbon and clipping after drying has been reported to increase yields as much as 4 percent. However, extra energy is used to dry some veneer that is then clipped out and not used to make plywood. If all conditions are favorable, it is possible to obtain high veneer recovery in a commercial plant. For example, Knutson (.3.4) reported 87 percent yield of 1 in-inch Douglas-fir from sound logs 20 to 23 inches in diameter. VENEER YIELDS (SLICED) In genel'al veneer recove, y is highest b:v ro­ tary cutting', less by flat-slicing, and least by quarter-slicing. Yields are less for slicing be­ cause of losses when sawing the flitches and \"hen clipping' straight edges on the relatiYely nHrrow sliced veneer. Some commercial slicing operators have re­ ported that, for logs 15 inches and larger in diameter, the yield of flat-sliced veneer is abont equal in equivalent thicknesses to the board foot value by the Scribner Decimal C log rule. 87 VOLUME 01" TIMBER NEEDED TO SET UP A VENEEH PLANT A typical plant in the United States making construction and industrial plywood llses ap­ proximately 40 million board feet of logs per year. The smallest economically suitable con­ struction plywood plant uses about 11) million board feet of logs a year. If the volume of wood available at a site is less than this, there is little point in considering it for structural plywood. Hardwood and decorative plywood plants are general1y smaller than ::;tructural plywood plants. In addition. they frequently use a variety of species, Therefore, ,,'hile 12 to 15 million lJoard feet of logs may be used in a year, a harch,'ood species that could be supplied at the rate of 5 million board feet a year could prob­ ably be llsed satisfactorily, An even greater diversity of species is cut by mills making face veneers. Manufacturers of face veneers state that it is imperative that a continuing suppl~' of a new faee veneer must be a\'ailable. Othendse the cost of advertising hnd other promotion needed te get a new species accepted is not warranted. Core and rl'ossband yeneer is generally not sllecified by the ultimate customer. Benee, in­ troducing a new species is Dot as difficult as with fare veneers. The technical 11l"Operties of the \Yood and the volume antilability at a rea­ sonable cost are important for core and cross­ band veneers. Container veneer often is made from a vari­ ety of species. Typical plants are small and use less volume of logs than plywood plants. The encl-produtt h; generally an expendable lo"\\"-cost container. Cheap stumpage is essential. Lo"wer quality logs than those acceptable for plywood panels are successfully used for container veneer. Two examples of the im]lOl'tance of avaHable timber are the development of Routhern pine softwood plywood and bickol'Y- or pecan-faced hardwooct plywood during' the 19GO's. Both of these groups of species are relatively difficult to process into veneer and plywood. Yet, because of the larg'e availalJle timber supply of each, ther became realities. Southern pine is challeng­ ingthe western soft\\"ood plywood inclusb'~', and hickory and pee-an are a major group used for decorative face veneel'. In some mixed forests of the tropieg, the totai stumpage is large. but no one species occurs in large volume. In these areas it is often difficult to exploit ne\\' species for veneer. This is true even for a species that has good technical prop­ ertieR for use as veneer. The cost of developing information on a new Rpecies, determining ho\\' it should be handled in production, introdudng it, and promoting it in a product line is \'ery costly. If a species is available only on a sporadic basis. it is gener­ ally not economical for a manufacturer to uti­ lize the species. 88 LITERATURE CITED 1. American Plywood Association 1973. How to control veneer dryer emISSIons. APA sem., reprinted in Wood and Wood Prod. Nov. 1973, p. 94 B,C,D. 2. Baldwin, Richard F. 1975. Plywood manufacturing practices. Miller Fraeman Pub., Inc. San Francisco. p. 260. 3. Bethel, James S., and Robert J. Hadel' 1952. Hardwood veneer drying. J. For. Pl·od. Res. Soc. 2 (5) :205-215. 4. Bryant, B., 'I'. Peters, and G. Hoerber 1965. Veneer thickness variation: its measure­ ment and significance in plywood manufacture. For. Prod. J. 15 (6) :233-237. 5. Burrell, J. F. 1973. Plywood plants of the future. Plywood and Panel Mag. 14(6) :28-30. Nov. S. Cade, J. C., and E. T. Choong 1969. Influence of cutting' velocity and log diam­ eter on tensile strength of veneer across the grain. For. Prod. J. 19 (7) : 52-53. 7. CollettI B. M., A. Brackley, and J. D. Cumming 1971. Simpiified, highly accurate method of pro­ ducing' high-quality veneer. For. Ind. 98 (1) : 62-65. B. Comstock, G. L. 1971. The kinetics of veneer jet drying. For. Prod. J. 21 (9) :104-111. 9. Dokken, H. M., and V. Godin 1975. Instrument for measuring' knife pitch angle on venee" lathes. For. Prod. J. 25(6): 44-45. June. 10. Feihl, A. O. 1959. Improved profiles for veneer knives. Can. Woodworker. Aug. 11. Feihl, A. O. 1972. Heating frozen and nonfrozen yen eel' logs. For. Prod. J. 22(10) :41-50. 12. Feihl, A. 0., and M. N. Carroll 1969. Rotary cutting veneer with a floating bar. For. Prod. J. 19 (10) :28-32. 13. Feihl, A. 0., H. G. M. Colbeck, and V. Godin 1965. The rotary cutting of Douglas-fir. Can. Dep. For., For. Prod. Res. Br., Pub. No. 1004. 14. Feihl, A. 0., and V. Godin 1967. Wear, play, and heat distortion in veneer lathes. Can. Dep. For., For. Prod. Res. Br., Pub. No. 1188. 15. Feihl, A. 0, and V Godin 1970. Setting veneer lathes with aid of instru­ ments. Can. Dep. For., For. Prod. Res. Br., Pub. No. 1206. 16. Feih1, A. 0., and V. Godin 1970. Peeling defects in veneer, their causes and control. Can. Dep. For., For. Prod. Res. Br., Tech. Note 25. 17. Fleischer, H. O. 1949. Experiments in rotary veneer cutting. J. For. Prod. Res. Soc. 3 :137-155. 18. Fleischer, H. O. 1953. Veneer drying rates and factors affect­ ing them. J. For. Prod. Res. Soc. 3(3) :27-32. 19. Fleischer, H. O. 1956. Instruments of alining the knife and nose­ bar on the veneer lathe and slicer. For. Prod. J. 6(1) :1-5. 89 20. Fleischer, H. O. 1959. Heating rates for logs, bolts, and flitches to be cut into veneer. U.S. For. Prod. Lab. Rep. No. 2149. 21. Fondronnier, J., and J. Guillerm 1967. Guide pratique de Ia derouleuse (Fr.). Cent. Tech. du Bois, 10 Ave. de St. Mancle, Paris 12e, Fr. 22. Fondronnier, J., and J. Guillerm 1975. Le Flambage du bois lors de son dcroulage. Cent. Tech. du Bois, 10 Ave. de St. Mancle, Paris 12e, Fr. 23. Foschi, R. O. 1976. Log centering errors and veneer yield. For. Prod. J. 26 (2) : 52-56. :Feb. 24. Godin, V. 1968. The grinding of veneer knives. Can. Dep. For., For. Prod. Res. Br., Pub. No. 1236. 25. Grantham, John and George Atherton 1959. Heating Douglas-fir blocks-does it pa~T? Oreg. For. Prod. Res. Center. Bull. No.9. 26. Hancock, W. V., and H. Hailey 1975. Lathe operators' manual VP-X-130. Can. West. For. Prod. Lab., Vancouver, B.C. Jan. 27. HalTar, L. S. 1954. Defects in hard wood veneer logs: their frequency and importance. USDA For. Servo Southeast. For. Exp. Stn. Pap. No. 39. Ashe­ ville, N.C. 28. Hillis, W. E. 1962. Wood extractives. Academic Press, N.Y. 513 p. 29. Hoadley, R. B. 1962. Dynamic equilibrium in veneer cutting. For. Prod. J. 12(3) :116-123. 30. Hann, R. A., R. W. Jokerst., R. S. Kurtenacker, C. C. PetE'l's, and J. L. Tschernitz. 1971. Rapid production of pallet deckboards from low-grade logs. USDA For. Ser. Res. Pap. 154. For. Prod. Lab., Madison, Wis. 31. Kivimaa, E. 1952. Was ist die Abstumpfung del' Holzbear­ beitungswerkzeuge? Holz als Roh- und Werkst. 10 :425-428. 32. Kivimaa, E., and M. Kovanen 1953. Microsharpening of veneer lathe knives. State Institute for Tech. Res., Helsinki, Finl., Rep. No. 126, 24p. 33. Knospe, Lothar 1d64. The influence of the cutting process in slicing and peeling on the quality of veneers. Holztechnologie (Wood Tech.) 5 (1) :8-14. (in Ger.) 34. Knudson, R. M., R. W. C. Scharpff, R. J. Mastin, and D. Barnes 1975. Effect of lathe settings on veneer yield. For. Prod. J. 25(10) :52-56. 35. Kubinsky, Eugen and Milan Sochor 1968. New softening treatment for beech logs before rotary peeling to veneers. For. Prod. J. 18 (3) :19-21. 36. Kubler, Hans 1959. Studies of growth stresses in trees. Holz als Roh- und Wel'kst. 17(1) :1-9; 17(2) :44-54; and 17 (3) :77-86. 37. Lockard, C. R, J. A. Putnam, and R. D. Carpenter 1963. Grade defects in hardwood timber and logs. USDA Agric. Handb. 244. 38. Lutz, John F. 1952. Measuring roughness of rotary-cut veneer. The Timberman 53 (5) :97,98,100. 39. Lutz, John F. 1956. Effect of wood-structure orientation on smoothness of knife-cut veneers. For. Prod. J. 6 (11) :464-468. 40. Lutz, John F. 1964. How growth rate affects properties of softwood veneer. For. Prod. J. 14(3) :97-102. 41. Lutz, John Ii'. 1970. Buckle in veneer. USDA For. Servo Res. Note FPL-0207. For. Prod. Lab., Madison, Wis. 42. Lutz, John F. 1972. Veneer species that grow in the United States. USDA For. Servo Res. Pap. FPL 167. For. Prod. Lab., Madison, Wis. 43. Lutz, John F., A. Mergen, ancl H ..Panzer 1967. Effect of moisture content and speed of cut on quality of rotary-cut veneer. USDA For. Servo Res. Note FPL-0176. For. Prod. Lab., Madison, Wis. 44. Lutz, John }<'., A. F. Mergen, and H. Panzer 1969. Control of veneer thickness during rotary cutting. For. Prod. J. 19 (12) :21-27. 45. Lutz, John F., and R A. Patzer 1966. Effects of horizontal roller-bar openings 011 quality of roller-cut southern pine and yel­ low-poplar veneer. For. Prod. J. 16(10) :15-25. 46. MacLean, J. D. 1946. Rate of temperature change in short­ length round timbers. Trans. ArneI'. Soc. Mech. Eng. 68(1:1):1-16. 47. McKenzie, W. M., and B. M. McCombe 1968. Corrosive wear of veneer knives. For. Prod. J. 18 (3) :45,46. 48. Meriluoto, J aakko 1971. Melting of birch bolts. Paperi ja Puu 53 (9) :493-497. 49. Nearn, W. T. 1955. Effect of water soluble extractives on the volumetric slu:inkage and equilibrium moisture content of eleven tropical and domestic woods. Bull. 598, Pa. State Univ., CoIl. of Agric., Agric. Exp. Stn., University Park, Pa. 50. Northcott, P. L., and D. C. Walser 1965. Veneer-roug1.ness scale. B. C. Lumber­ man. July. 51. Northeastern Forest Experiment Station 1965. A guide to hardwood log grading. USDA For. Serv., Northeast For. Exp. Stn. Handb., Rev., Upper Darby, Pa. 52. Northern Hardwood and Pine Manufacturers Association 1968. Official grading rules for northern hard­ wood and softwood, logs and tie cuts. Green Bay, Wis. 53. Palka, L. C. 1974. Veneer cutting review. VP-X-135. Can. West. For. Prod. Lab., Vancouver, Carlada. 54. Peters, C. C., and A. Mergen 1971. Measuring wood surface smoothness: a proposed method. For. Prod. J. 21(7) :28-30. 55. Pillow, Maxon Y. 1943. Compression wood: importance and detec­ tion in aircraft veneer and plywood. U.S. For. Prod. Lab. Rep. No. 1586. Madison, Wis. 56. Pillow, Maxon Y. 1955. Detection of figured wood in standing trees. U.S. For. Prod. Lab. Rep. No. 2034. Madison, Wis. 57. Pillow, Maxon Y. 1962. Effects: of ten,,'Jn wood in harclwood lum­ ber ancl VE.lleer. U.S. For. Prod. Lab. Rep. No. 1943. Madison, Wis. 58. Puget Sound Log Scaling and Grading Bureau Columbia River Log Scaling and Grading Bureau Grays Harbor Log Scaling and Grading Bureau Southern Oregon Log Scaling and Grading Bureau Northern California Log Scaling and Grading Bureau 1969. Official log scaling and grading rules. Portland, Oreg. 59. Resch, H., C. A. Lofdahl, F. J. Smith, and C. Erb 1970. Moisture leveling in veneer by mkrowaves and hot air. For. Prod. J. 20 (10) :50-58. 60. Scheffer, T. C. 1969. Protecting stored logs and pulpwood in North America. Sonderdruck aus: Mater. und Organismen 4 Heft 3, 167-199. Verlag: Dunc­ kel' and Humblot, Ber!' 41. 61. Sche.ffer, T. C., and R M. Lindgren 1940. Stains of sapwood and sapwood products and their control. USDA Tech. Bull. No. 714. 62. Selbo, M. L. 1975. Adhesive bonding of wood. U.S. Dep. Agric., Tech. Bull. No. 1512. 63. U.S. Department of Commerce Hardwood and decorative plywood. Prod. Stand. PS 51-71. 64. U.S. Department of Commerce Construction and industrial plywood. Prod. Stand. PS 1-74. 65. U.S. Forest Products Laboratory, Forest Service 1974. Wood Handbook. U.S. Dept. Agric., Agric. Handb. No. 72, Rev. 66. U.S. General Services Administration Boxes, wood, wirebound. Fed. Specif. PPP-B­ 585b. 67. Walser, D. C. 1975. Preloading the pressure-bar assembly for improved veneer-lathe setting accuracy. For. Prod. J. 25 (7) :44-45. July. 68. Woodfin, Rkhard 0., Jr. 1973. Wood losses in plywood production. For. Prod. J. 23 (9), Sept. 90 APPENDIX I-NOMENCLATURE OF WOOD SPECIES AND VENEER Accurate identification is the key to efficient utilization of individual wood species. Wood is made up of a vast number of spec"es, each with its own properties, and known by a variety of common names. Only the precise name properly identifies aJ: individual species. Included here are the official common name of a species and the corresponding botanical name. In turn, these wood names are tied to the names for veneer. NOMENCLATURE OF WOOD SPECIES AND VENEER Commercial name of veneer General Official common tree name Botanical name Specific UNITED STATES HARDWOODS Alder American ash Aspen Nepal alder Red alder Black ash Oregon ash Pumpkin ash ViThite ash Shamel ash Popple Basswood Beech Birch Box elder Buckeye Butternut Cherry Cottonwood Elm Rock elm Soft elm Eucalyptus Gum Hackberry Hickory Holly Koa Locust Madrone Magnolia Nepal alder Red alder Black ash Oregon ash Pumpkin ash Blue ash Green ash White ash Shamel ash Bigtooth aspen Quaking aspen American basswood White basswood American beech Yellow birch Sweet birch Paper birch Alaskan paper birch Gray birch River birch Box elder Ohio buckeye Yellow buckeye Butternut Black cherry Balsam poplar Black cottonwood Eastern cottonwood Swamp cottonwood Cedar elm Rock elm Winged elm American elm (gray elm) Slippery elm (red elm) Robusta eucalyptus Sweetgum Hackberry Sugarberry Mockernut hickory Pignut hickory Shagbark hickory Shellbark hickory American holly Koa Black locust Honeylocust Pacific madrone Cucumbertree Southern magnolia Sweetbay 91 Alnus nepalensis A. rubra Fraxinus nigra F. lati/olia F. profunda F. quadrangulala F. pennsylvanica F. americana F. uhdei Populus grandidenlata P. lremuloides Tilia americana T. helerophylla Fagus grandi/olia Betula alleghaniensis B. lenta B. papyri/era B. papyrijera var. humilis B. populi/olia B. nigra Acer negundo Aesculus glabra A.ociandra Juglans cinerea Prunus serotina Populus balsamifera P. trichoco.rpa P. deltoideI) P. heterophylla Ulmus crassi/olia U.lhomasii U. alala U. americana U. mbra Eucalyptus robusla Liquidambar slyracifiua CeUis occidentalis C. laevigata Carya tomenlosa C. glabra C. ovalo. C. laciniosa flex opaca Acacia koa Robinia pseudoacacia Gledilsia tr1·acanthos Arbutus menziesii kf aynolia acuminala M. yrandifiora M. viryiniana NOMENCLATURE OF WOOD SPECIES AND VENEER-continued Official common tree name Commercial name of veneer General Maple Oak Ohia Oregon myrtle Pecan Persimmon Poplar Sassafras Silk-oak Sycamore Tanoak Teak Tupelo Walnut Willow Yagrumo hembra Cedar Cypress Botanical name Specific UNITED STATES HARDWOOD-continued Black maple Sugar maple Bigleaf maple Oregon maple Red maple Soft maple Silver maple Black oak Red oak California black oak Cherrybark oak Laurel oak Northern red oak Nuttall oak Pin oak Scarlet oak Shumard oak Southern red oak Water oak Willow oak Bur oak White oak Chestnut oak Chinkapin oak Delta post oak Durand oak Live oak Oregon white oak Overcup oak Post oak Swamp chestnut oak Swamp white oak White oak Ohia California laurel Bitternut hickory Nutmeg hickory Water hickory Pecan Common persimmon Yellow-poplar Sassafras Lacewood American sycamore Tanoak Teak Black tupelo Swamp tupelo Water tupelo Black walnut Black willow Yagrumo hembra Hard maple UNITED STATES SOF'£WOODS Alaska-cedar Alaska cedar Incense-cedar Incense cedar Port-Orford-cedar Port Orford cedar Eastern redcedar Eastern red cedar Western red cedar Western red cedar Northern white-cedar Northern whit"l cedar Atlantic white-cedar Southern white cedar Baldcypress Pond cypress 92 Acer nigrum A. saccharum A. macrophyllum A. rubrum A. saccharinum Quercus velulina Q. kelZoggii Q. falcala var. pagodaefolia Q. Zat~rifolia Q. rubra Q. nuttallii Q. palustris Q. coccinea Q. shumardii Q. falcata Q. nigra Q. phelZos Q. macrocarpa Q. prinus Q. muehlenbergii Q. stcUata var. mississippiensis Q. durandii Q. virginiana Q. garryana Q. lyrata Q. stellala Q. michauxii Q. bicolor Q. alba M ctrosideros polymorpha UmbelluZaria californica Carya cordiformis C. myristicaeformis C. aquatica C. illinoensis Diospyros virginiana Liriodendron luZipifera Sassafras albidum Grevillea robusta Platanus occidentalis Lithocarpus densifiorus Tectona grandis Nyssa sylvatica N. sylvatica var. bifiora N. aquatica Juglans nigra Salix nigra Cecropia peltata Chamaecyparis nootkatensis Libocedms decurrens Chamaecyparis lawsoniana Juniperus virginiana Thuja plicata T. occidentalis Chamaecyparis lhyoides Taxodiunt distichum T. distichum var. nutans NOMENCLATURE OF WOOD SPECIES AND VENEER-continued Commercial name of veneer General Official common tree name Botanical name Specific UNITED STATES SOFTWOODs-continued Fir Balsam fir Douglas-fir Noble fir White fir Hemlock Juniper Western larch Pine Eastern hemlock Mount.ain hemlock West Coast hemlock Western juniper Digger pine Jack pine Jeffrey pine Knobcone pine Limber pine Lodgepole pine Norway pine Ponderosa pine Sugar pine Idaho white pine Northern white pine White bark pine Southern pine Redwood Spruce Eastern spruce Engelmann spruce Sitka spruce Tamarack Paci.fic yew Balsam fir Coast Douglas-fir Interior west Douglas-fir Interior north Douglas-fir Interior south Douglas-fir Noble fir Subalpine fir California red fir Shasta red fir Grand fir Pacific silver fir White fir Eastern hemlock Mountain hemlock Western hemlock Alligator juniper Rocky Mountain juniper Western juniper Vi estern larch Digger pine Jack pine Jeffrey pine Knobcone pine Limber pine Lodgepole pine Red pine Ponderosa pine Sugar pine Western white pine Eastern white pine White bark pine Loblolly pine Shortleaf pine Longleaf pine Slash pine Spruce pine Pond pine Virginia pine Pitch pine Sand pine Table-Mountain pine Big tree Redwood Black spruce Red spruce White spruce Blue spruce Engelmann spruce Sitka spruce Tamarack !'acific yew Abies balsamea Pseudotsuga menziesii P. menziesii P. menziesii var. glauca P. menziesii var. glauca Abies procera A. lasiocarpa Abies magnifica A. magnifica var. shastensis A. grandis A. amabilis A. concolor T. canadensis T. mertensiana T. heterophylla .Tuniperus deppeana .T. scopulorum .T. occidentalis Larix occidentalis Pinus sabiniana P. banksiana P. jeffreyi P. attenuala P. fiexilis P. contorta P. resinosa P. ponderosa P. lambertiana P. monticola P. strobus P. albicaulis Pinus taeda P. echinala P. palustris P. ellioltii P. glabra P. serolina P. virginiana P. rigida P. clausa P. pungens Sequoia gigantea S. sempervirens Picea mariana P. rubens P. glauca P. pungens P. engelmannii P. sitchensis Larix laricina Taxus brevijolia OTHER SPECIES IMPORTANT To U.S. VENEER Alpine ash Angelique Apitong Avodire Brazil nut Bubinga Cativo Alpine ash Angelique Keruing Avodire Brazil nut Bubinga Ca.tivo 93 Eucalyptus gillanlea Dicorynia guianensis DipleroCarl)US Bpp. Turraeanlhus ajricanus Berlhollelia excelsa Guibourlia spp. Prioria copaifera NOMENCLATURE OF WOOD SPECIES AND VENEER-continued Commercial name of veneer Official common tree name Botanical name Specific General OTHER SPECIEs-continued Ceiba Determa Kapur Keruing Klinki Lauan Dark red Light red Light red Light red Limba Mahogany Mengkulang Meranti Mersawa Muritinga Okoume Paldao Primavera Rosewood Sapele Teak Caribbean pine Ocote pine Ceiba Determa Keladan Apitong Klinki pine Philippine mahogany Tangile Almon Bagtikan Mayapis Limba Honduras mahogany African mahogany Mengkulang Meranti Palosapis Muritinga Okoume Paldao Primavera Rosewood Sapele Teak Caribbean pine Ocote pine 94 Ceiba pentandra and samauma Oeotea rubra Dryobo,lanops spp, Dipteroearpus spp, Arauearia klinkii Shorea polysperma S. almon Parashorea plieata S. squamata Terminalia superba Swietenia maerophylla Khaya spp. Tarrietia spp. Shorea spp. Anisoptera spp. M aquira spp. Aueoumea klaineana Draeontomelon spp. Cybistax donnell-srniihii Dalbergia spp. Eniandrophragma eylindrieurn Teetona grandis Pinus earibaea Pinus ooearpa APPENDIX I1--PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER The column on specific gravity of the wood gives a quick comparison between species. In general, the higher the specific gravity, the higher the strength properties such as hard­ ness and stiffness and the greater the shrink­ age. The green moisture content is givtn to the closest 10 percent for both sapwood and heart­ wC'od. If the moisture content of the sapwood and heartwood is very different, it may pay to separate sapwood and heartwood veneer for drying. Very high moisture contents, such as over 100 percent, may indicate problems in cut­ ting and drying vene.:.', from this species. Permeability is listed as P, permeable; M, moderately permeable; or R, refractory. Shrinkage is given under three subheads: Tangential, radial, and volumetric. Tangential shrinkage indicates the widthwise shrinkage of . 95 rotary-cut and flat-sliced veneer, while radial shrinkage is an estimate of the widthwise shrinkage of quarter-sliced veneer. Since these figures are given from green to ovendry, they can be interpolated for other moisture condi­ tions. In general, shrinkage is considered to be a straight-line relationship from a moisture content of 30 percent (green) to 0 percent. The volumetric shrinkage, together with spe­ cific gravity, can be used to describe the wood nn the basis of weight at any moisture content. The columns describing arrangement and size of vessels in hardwood veneer contribute to an understanding of the figure of this ve­ neer. Small pores are under 100 microns in diameter; medium pores 100 to 150 microns; and large pores over 150 microns. The grain direction and color of the sap­ wood and heartwood are self-explanatory. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER Common name Green Specific moisture gravity (green content volume HeartSapand oveadry wood wood weight) Permeability I Sapwood Vessel (pores) Shrinkage green to ovendry Heartwood Tangen- Radial tial Volumetric Arrangement Grain Coior of sapwood and heartwood Size (texture) -------_. Pet Pet Pet Pet Pet UNITED STATES HARDWOODS Alder Nepal 0.34 90 6.8 4.0 10.8 Diffuse porous Medium Straight 7.3 4.4 12.6 ... do ... . , .do ... ... do ... 7.8 5.0 15.2 Ring porous Large ., .do ... 6.5 3.9 11.7 ... do ... ... do ... ... do ... 7.1 8.1 4.6 4.1 12.5 13.2 ... do ... ... do ... .. . do ... ... do ... ... do ... ., .do ... 6.3 3.7 12.0 ... do ... .. . do ... ... do ... 7.4 3.5 10.2 .. . do ... " .do ... ., .do ... 7.8 4.9 13.4 .. . do ... ... do ... ., .do ... to 190 ~ 100 Red .37 Ash Black .45 Blue .53 Green Oregon . 53 .50 Pumpkin . 48 Shamel .47 50 White . 55 40 P P 90 0"> P 60 50 50 P Sapwood nearly white. Heartwood pink-white. Both become light tan with a roseate cast during drying. Sapwood white turning to pale pink-tan on expo­ sure. Heartwood pale pir.k-tan. Similar to white ash but the heartwood is a darker warm brown. White to pale yellow sap­ wood, the heartwood is very light brown . ...... . do ....... Similar to white ash but the heartwood sometimes has a reddish tinge. White to pale yellow sap­ wood, the heartwood is very light brown. Sapwood is nearly white and merges gradually in to the ligh t-tan heart­ wood. White to pale yellow sap­ wood. The heartwood is very light brown. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Specific gra\ ity (green volume and ovendry weight) ----.­ Green moisture content Sapwood Sapwood Heartwood ........ -~---~ Pet Permeability - -~-~-----~~. 1 Shrinkage green to ovendry Heart­ wood Tangen- Radial tial -~----- Pel ~-~---.,--"~-- Pet Pel - Volu­ metric ----­ ---~ Vessel (pores) Arrangement _. _ _ L._.__ Grain Size (texture) ~. _~ Color of sapwood and heartwood ____ Pet UNITED STATES HARDWOODS-continued Aspen Bigtooth Quaking Basswood American .35 90 .35 110 .32 130 M 7.9 3.3 11.8 Diffuse porous Small Usually straight 100 M 6.7 3.5 11.5 ... do ... ... do ... .. . do ... 80 P 9.3 6.6 15.8 ... do ... ... do ... Straight Diffuse porous Small Straight White to ..;J Beech, American 0.56 70 60 Birch Alaskan paper .49 60 60 Gray .45 Paper River Sweet Yellow Buckeye Ohio .48 .49 .60 .55 Yellow .33 70 90 70 70 80 70 140 140 P M P P P P-R M P M M 11.9 5.5 16.3 .. . do ... ... do ... Straight to inter­ locked 9.9 6.5 16.7 ... do ... Small Straight 9.5 5.2 14.7 ... do ... Medium Straight to curly 8.6 9.2 9.0 9.5 6.3 4.7 6.3 7.3 16.2 13.9 15.6 16.7 ... do ... ... do ... ... do ... ... do ... ... do ... . .. do ... ., .do ... ... do ... .. .do ... . .. do ... .. . do ... ... do ... ... do ... Small Straight ... do ... . .. do ... . .. do ... 8.1 3.6 12.5 Sapwood white to cream merging into cream to light gray-brown heartwood. . ...... do ....... Sapwood creamy white merging gradually to pale brown P1artwood. Sapwood creamy white merging gradually to pale brown heartwood. Sapwood white tinged with red. Heartwood light red-brown. Sapwood nearly white, may brown slightly during drying at high temper­ atures. Heartwood is light reddish-brown. Sapwood white to pale yellow. Heartwood light to dark brown or reddishbrown. . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... White sapwood merging gradually to creamy white to pale yellow heart-wood. Frequent gray streaks. . ...... do ....... --- ~~~~. Common name ~ __ • ....-_._"r'•. ~. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER--continued ____"'"_·"" .___ __ .______ __• ____ "",,~ _ _ _ . __• _".~ ___ ~ __ ,~ ___ Green Specific moisture gravity Sapcontent (green volume --~---.---- wood HeartSapand wood ovendry wood weight) ~> _______ 4~_'_'~_' ~ Shrinlmge green to ovendry Heart- - - - . - - - - . - - - - - wood Tangen- Radial Volumetric tial Permeability ------- Pet Pet Pet .. ~- --... Grain Color of sapwood and heartwood Size (texture) Arrangement -~- Pet .'r._~~~_"" Vessel (pores) 1 ~-~.- Pet UNITED STATIcS HARDWOODs--continued Butternut .36 Cherry, Black .47 Cottonwood Balsam poplar (Balm of Gilead) .30 100 Sapwood white to light gray-brown. Heartwood a buttery-tan with occa­ sional dark streaks. Sapwood nearly white. Usually Heartwood light to dark straight red-brown, darkens with exposure. ... do ... 100 6.4 3.4 10.6 SemidifTuse porous Medium 60 7.1 3.7 11.5 DifTuse porous Small M 7.1 3.0 10.5 ... do ... .. . do ... ... do ... (,0 00 Sapwood white gradually merging into gray-white to light brown heart­ wood . ....... do ........ ....... do, ...... Sapwood white gradually merging into gray-white to light gray-brown heartwood. .31 .37 150 160 P M M M 8.6 9.2 3.6 3.9 12.4 14.1 ... do ... .. . do ... " .do ... .. . do ... .. . do ... .. ,do ... . , .do ... ., .do ... ... do ... Elm American .46 90 100 P M 9.5 4.2 14.6 Ring porous Large Sapwood gray-white, Heartwood light gray­ brown, often tinged with reel. Cedar .5H 60 70 10.2 4.7 14.9 ... do .. , Rock Slippery .57 60 40 8.1 8.9 4.8 4.9 14.1 13.8 ... do ... .. . do ... Variable (small) Small Large Straight; sometimes interlocked . , .do ... . , .do ... ... do ... Winged .60 11.6 5.3 16.9 ... do ... Small .... , .. do ....... Sapwood gray-white, Heartwood light red­ brown to dark red-brown or chucolate brown. May have yellow streak~. Sapwood gray-white . Heartwood light gray­ brown, often tinged with red. Black Eastern Swamp ,48 R P . , .do ... ....... do ....... PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Specific gravity (green volume and ovendry weight) Green moisture content Sapwood Heartwood Pet Pet Permeability Sapwood I Shrinkage green to ovendry Heart­ wood Tangen- Radial tial Volu­ metric Pet Pet Pet Vessel (pores) Arrangement Grain Size (texture) Color of sapwood and heartwood UNITED STATES HARDWOODs-continued Eucalyptus .60 70 Hackberry .49 70 90 to 100 60 0.60 50 SO 60 60 to 100 70 SO to 90 Hickory, pecan Bitternut R 10.7 6.1 S.9 4.S P Diffuse porous Medium Interlocked 16.9 Ring porous Large Straight; some­ times inter­ locked 13.6 Semiring porous Large Straight S.9 4.9 13.6 13.6 13.6 ... do ... ... do ... ., .do ... Large . .. do ... ...do ... ... do ... ... do ... ... do ... Sapwood white to light pink-tan. Heartwood reddish-brown with darker streaks . ...... do ....... . ...... do ....... . ...... do ....... 11.0 11.5 7.7 7.2 17.9 17.9 ... do ... ., .do ... . .. do ... .. .do... . ...... do ....... . ...... do ....... 10.5 12.6 9.9 7.0 7.6 4.S 16.7 19.2 16.9 ... do ... Ring porous .. . do ... ... do ... Diffuse porous ... do ... .. . do ... Sman . .. do ... ... do ... ... do ... 6.6 4.2 10.S Ring porous Large ... do ... 6.2 5.5 Diffuse porous Medium Straight to very irregular . ...... do ....... . ...... do ....... White sapwood and ivory­ white heartwood turning brown with exposure. Cream colored sapwood and warm light red­ brown heartwood. Sapwood is narrow and yellow-white. Golden brown heartwood may have shades of red. Veneer from old trees may have black streaks. to to Nutmeg Pecan Water .56 . 60 .61 Hickory, true Mockernut Pignut .64 .66 50 50 SO 70 P P Shagbark Shellbark Holly, American .64 . 62 .50 50 70 SO SO P P P Honeylocust . 60 Koa .53 60 to 100 P P P M P Sapwood cream to light brown. Heartwood is reddish-pink. Sapwood pale yellow to greenish-gray. Heart­ wood same as s,\pwood but darker. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name ... ---~ Specific gravity (green volume and ovendry weight) Green moisture content Sapwood Heartwood Pet Pet ....-""" Shrinkage green to ovendry Heart- - - - " wood Tangen- Radial Volumetric tial Permeability Sapwood ~----'-- ... ------~' -~~-....- 1 Vessel (pores) Arrangement Grain Color of sapwood and heartwood Size (texture) -----'_._- -'>-­ Pet Pet Pet UNITE)) STATES HARDWOODs-continued ~ Laurel, California .51 70 70 Locust, Black .66 40 40 0.58 140 to 170 120 Madrone, Pacific 0 0 Magnolia Cucumbertree R .44 Southern .46 Sweetbay .42 100 80 Maple Bigleaf .44 P Black .fi2 P M 8.5 2.9 11.9 ... do ... Small Straight to inter- locked 7.2 4.6 10.2 Ring porous Large Straight 12.4 5.6 18.1 Diffuse porous Medium Straight; occasionally irregular 8.8 5.2 13.6 ., .do ... Small Straight 6.6 5.4 12.3 ... do ... .. . do ... ... do ... 8.3 4.7 13.0 .. . do ... .. . do ... ... do ... 7.1 3.7 11.6 ... do ... 9.3 4.8 14.0 ... do ... Straight; Small to occasionmedium ally curly or wavy grained Small ... do ... Sapwood white to light brown. Heartwood golden brown. Some­ times yellowish-green, often with darker streaks. Narrow sapwood white to cream. Heartwood golden brown with greenish tinge. Sapwood white often with pink tinge. Heartwood light pink to red-brown and gray-green. Sapwood white. Heartwood light yellow-green. Oc­ casional dark green or purple streaks. Reported dark streaks more common than in yellow-poplar. Sapwood white. Heartwood light yellow-green. Oc­ casional dark green or purple streaks. Sapwood reddish-white. Heartwood pink-brown. White sapwood may be tinged red-brown. Uni­ form light red-brown heartwood. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Specific gravity (green volume and ovendry weight) Green moisture content Sapwood -~-".~~~,. Pet Maple (cont.) Boxelder i-' 0 i-' Heartwood Heart­ wood Tangen- Radial tial --------­ --.~-----,.--- Pet Pet .41 .49 Silver Sugar Oak, red Black .44 .56 Chinkapin Delta post Durand Sapwood Shrinkage green to ovendry Volu­ metric Vessel (pores) Arrangement Grain Size (texture) Color of sapwood and heartwood -~ . .------~-- Pet Pet UNITED STATES HARDWOODs-continued Red California black Cherrybark Chestnut Laurel Northern red Nuttall Pin Scarlet Shumard Southern red Water Willow Oak, white Bur Permeability 1 100 70 60 70 0.56 . 51 .61 .57 . 56 .56 80 80 70 70 80 .58 .60 . 58 .60 80 80 70 80 80 80 3.9 11.1 ... do ... ... do ... . .. do ... P M 8.2 4.0 13.1 ... do ... .. . do ... . .. do ... P P M M 7.2 9.9 3.0 4.8 12.0 14.9 ... do ... ... do ... . , .do ... ., .do ... .. . do ... . .. do ... P P 11.1 4.4 14.2 Ring porous Large Straight P P P P P P P P P P M 6.6 10.6 10.8 9.9 8.6 3.6 5.5 5.3 4.0 4.0 12.1 16.1 16.7 19.0 13.5 9.5 10.8 4.3 4.4 14.5 13.8 11.3 9.8 9.6 4.7 4.4 5.0 16.3 16.4 18.9 ... do ... ... do ... .. . do ... ... do ... .. . do ... .. . do ... ... do ... ... do ... . , .do ... ., .do ... ... do ... ... do ... ... do ... ... do ... ... do ... ... do ... ... do ... .. . do ... .. . do ... ... do ... ... do ... ... do ... ... do ... ... do ... . .. do ... . .. do ... . .. do ... .. .do ... .. .do... ... do ... ... do ... . .. do ... . .. do ... .. .do ... .. .do ... . .. do ... 8.8 4.4 12.7 ... do ... .. . do ... . .. do ... .. . do ... . , .do ... .. . do ... ... do ... ... do ... ... do ... ., .do ... .. .do ... .. .do ... P P P P P P P p R p R p .52 . 56 . 56 7.4 Green-yellow sapwood sometimes with red streaks. Heartwood yellowish-bronze. White sapwood may be tinged red-brown. Uni­ form light red-brown heartwood . . ...... do ....... . ...... do ....... Sapwood generally white. Heartwood of the red oak group usually has a pink tinge but may resemble heartwood of white oaks. . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... . ...... do ....... Sapwood generally white . Heartwood of the white oak group is light or pa:e gray-brown occasionally, has a reddish tinge. . ...... do ....... . ...... do ....... . ...... do ....... -. ~ _._._-- ~"--.-- PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued "- ------- -----~---~--... -------- ------"~ .~.-........--.---. -~"--~-.~-.-..-.~- ~"......-...--.-.,-"~--.-. Common name Green Specific moisture gravity content (green volume HeartSapand wood ovendry wood weight) --~- -.--,-----<--~--. Pet Permeability Sapwood - - ...... Shrinkage green to ovendry 1 Heart- ­ wood Tangen- Radial tial -.---,--~-"~ .. Arrangement Grain Color of sapwood and heartwood Sapwood white to graybrown. Heartwood dull brown to gray-brown. Sapwood generally white. Heartwood of the white oak group is light or pale gray-brown, occasionally has a reddish tinge . ....... do ....... Size (texture) ,~-.----- Pet Pet Volumetric Vessel (pores) Pet Pet UNITED STATER HARDWOODs-continued Oak (cont.) LiYe Oregon white Overcup ~ 0 l'\J Post Swamp chestnut Swamp white White Ohia .81 50 50 .64 0.57 .60 .60 .64 .60 .70 90 80 to to 110 120 80 60 60 P R 9.5 6.6 14.7 Diffuse porous Small Irregular P R 9.2 4.2 13.4 Ring porous Large Straight P R 12.7 5.3 18.0 .. . do ... . , .do ... .. . do ... P P P P R R R R 9.8 10.8 5.4 5.2 10.5 12.1 5.6 6.9 16.2 16.4 17.7 15.8 19.1 .. . do ... .. . do ... .. . do ... .. . do ... Diffuse porous .. . do ... .. . do ... ., .do ... .. . do ... Small 11.2 7.9 19.1 Semiring porous Medium to large 6.2 4.0 10.3 Ring porous Large .. . do ... .. . do ... . , .do ... ... do ... Straight to mildly irregular Straight to interlocked Straight 7.7 2.7 Diffuse porous Medium .. . do ... 7.3 5.0 Ring porous Large Straight; some­ times interlocked to 70 Persimmon, common .64 Sassafras .42 Silk-oak .51 60 60 100 to 130 Sugarberry .47 12.7 ....... do ....... ....... do ....... . ..... do ....... ....... do ....... Light yellow-brown sap­ wood. The heartwood is dark brown with a reddish cast. Sapwood creamy white darkening to gray-brown. Heartwood dark brown with black stripes. Sapwood light yellow. Heartwood dull gray­ brown to orange-brown . Sapwood is white. The heartwood is light pink and turns to light pink­ tan on exposure to sun­ light. Sapwood pale yellow to greenish-gray. Heart­ wood same as sapwood but darker. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued ---_._---"-.--.-- Common name Specific Green gravity moisture (green content volume and SapHeartovendry wood wood weight) Permeability Sapwood - ___. Sweetgum .46 Pet Pet 140 80 Shrinlmge green to ovendry 1 Heart- --~ wood Tangen- Radial tial ~_··~r~· _ ___ -- - .,- ~ Pet Volumetric Vessel (pores) Arrange1l1ent -'"--------~- Pet P UNITED STATES HARDWOODs-continued R 10.2 5.3 15.0 Diffuse porous R to Small Frequently interlocked 120 ,46 130 110 P Tanoak 0.58 80 100 P Teak .5!) Sycamore, Anwrican 90 8.4 5.0 14.2 .. . do ... . .. do ... Interlocked 13.0 6.0 14.9 ... do ... Medium Straight 6.6 2.4 Ring to semidiffuse porous Large ... do ... Diffuse porous Small Usually interlocked ., .do ... ... do. . .. do ... ... do ... .. . do ... . .. do ... to ...... 110 0 co Tupelo Blackgum ,46 120 90 P P 8.7 5.1 13.9 Swamp Water . 45 ,46 150 140 120 150 P P P 7.0 7.6 4.2 12.5 \Valnut, Black .51 70 7.8 5.5 12.8 Semiring porous Medium Straight to irregular Willow, Black .34 HO 8.7 3.3 14.4 Nearly diffuse porous Small Yagrumo hembra .26 110 7.5 1.7 Diffuse porous Medium Straight to interlocked Straight 8.2 4.6 ... do ... Small . .. do ... 90 160 M to 180 Yellow-poplar .'10 110 80 p R Color of sapwood and heartwood Size (texture) <-.-~-----~- -.---.~-- -----~ Pet Grain 12.3 Sapwood is pinkish-white. Heartwood is reddish­ brown, often with ir­ regular dark streaks. Sapwood pale reddish­ brown. Heartwood is deeper red-brown but not sharply defined from the sapwood. Sapwood light tan. Heart­ wood light red-brown. Sapwood white to pale yellow-brown. Heart­ wood yellow-brown to rich brown frequently with irregular dark streaks. White sapwood. Pale brown-gray heartwood. Heartwood may be darker than water tupelo. . ...... do ....... White sapwood. Pale brown-gray heartwood. Light pale brown sapwood darkened by steaming. Heartwood light gray­ brown to dark purplish­ brown. Sapwood whitish. Heart­ wood pale brown to gray-brown. All the wood appears to be sapwood. It is white when first cut and dries to a creamy white color. Sapwood white. Heartwood light yellow green. Oc­ casional dark green or purple streaks. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENgER---continued --.--~.~- ....~-..,...~-- ....... -~.~<" Common name -------. ~--. Specific gr<.vity (green volume and ovendry weight) Green moisture content Sapwood Permeability Sapwood Heart­ wood I Shrinkage green to ovendry Heart­ wood Tangen" Radial tial ----.--.--------.- --­ PrJ --'''. Pet Grain Color of sapwood and heartwood Narrow sapwood, white to yellow merging into bright clear yellow heart­ wood. Thin sapwood, light in color, light brown heart­ wood with a pink tinge. Thin white sapwood and bright purplish-red to dull red heartwood. Thin whitish sapwood, heartwood reddish­ brown to dull brown, sometimes with a pur­ plish tinge. Sapwood nearly white. Narrow heartwood uni­ formly straw brown. Thin light-colored sap­ wood merges into the light yellow or pale brown heartwood. Sapwood nearly white . N arrow heartwood red­ dish or pinkish-brown to dull brown. Volumetric .. -~.- Pet Pet -----_._-'"*"'-- Contrast in density from springwood to summerwood ~.--~-. Pet UNITED STATES SOFTWOODS Cedar Alaska­ >P- 170 R 30 6.0 2.8 9.2 Fille uniform texture, faint growth ring Straight Atlantic wl1ite­ .31 40 5.2 2.8 8,4 More or less gradual ... do ... Eastern red cedar .44 30 4.7 3.1 7.8 Gradual to abrupt, late­ wood distinct ... do ... Incense­ . 3~;) 210 40 5.2 3.3 7.6 Gradual transition, faint growth ring ... do ... Northern white­ .29 Mixed 55 R R 4.7 2.1 7.0 Morr. or less gradual transition Usually straight Por~Orford- .40 100 50 P M 6.9 4.6 10.1 Usually fine, uniform texture, fahlL growth ring Straight 'Western redcedar .37 250 60 R R 5.0 2.4 7.7 More or less abrupt, latewoocl is narrow .. . do ... .42 170 120 M 6.2 3.8 10.5 More or less abrupt Usually straight l-' 0 0.42 Cypress Baldcypress Sapwood pale yellowish­ white, merging into heartwood. Heartwood very variable in color ranging from yellowish to light or dark brown, reddish-brown, or al­ most black. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Specific gravity (green volume and ovendry weight) Green moisture content Sapwood Heartwood Pet Pet Permeability 1 Sapwood Shrinkage green to ovendry Heart­ wood Tangen- Radial tial Volu­ metric Pet Pet Pet Contrast in density from springwood to summerwood Grain Color of sapwood and heartwood More or less abrupt Usually straight Sapwood pale yellowish­ white, merging into heartwood. Heartwood very variable in color ranging from yellowish to light or dark brown, reddish-brown, or almost black. Abrupt transition ... do ... ......... do ......... ......... do ......... ......... do ........ . .. do ... . .. do ... ... do ... Sapwood whitish to pale yellowish or reddish­ white. Heartwood yellow­ ish or pale reddish­ yellow to orange-red or deep red. . ...... do ....... . ...... do ....... . ...... do ....... Transition gradual, latewood distinct Straight UNITED STATES SOFTWOOD5--continued Cypress (cont.) Pondcypress Douglas-fir Coast M .45 120 40 M M-R 7.8 5.0 11.8 ...... 0 01 Interior north Interior south Intedor west Fir Balsam .45 .43 .46 150 110 110 30 30 30 .34 Mixed 120 California red .36 Grand Noble .35 .37 Pacific silver 0.40 Mixed 35 to 230 140 60 to 130 130 to 200 90 40 to 50 40 to 50 R R R R 7.1 2.5 9.0 M M-R 6.9 3.8 11.8 ......... do ......... ... do ... M M R R 7.2 8.3 3.2 4.5 10.6 12.5 ......... do ......... ......... do ......... . .. do ... ... do ... M M 10.0 4.5 14.1 Transition gradual, latewood distinct Straight Heartwood and sapwood indistinguishable, nearly white. Heartwood may be gray. Heartwood and sapwood indistinguishable, white springwood, narrow summerwood with a light reddish-brown tinge. ....... do ....... . ...... do ....... Heartwood and sapwood indistinguishable, white springwood, narrow summerwood with a slight reddish-brown tinge. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Specific gravity (green volume and ovendry weight) Green moisture content Sapwood Heartwood Pet Pet Permeability 1 Sapwood Shrinkage green to oven dry Heart­ wood Tangen- Radial tial Pet Pet Grain Color of sapwood and heartwood ......... do ......... . .. do ... Heartwood and sapwood indistinguishable, white springwood, narrow summerwood with a light reddish-brown tinge . ....... do ....... . ...... do ....... Contrast in density from springwood to summerwood Volu­ metric Pet UNITED STATES SOFTWOODs-continued Fir (cont.) Shasta red .36 Subalpine White .31 .37 M R 50 25 M-R R R 7.1 7.0 2.5 3.2 9.0 9.4 ........ . do ......... ........ . do ......... .. . do ... ... do ... 180 40 M-R R 6.8 3.0 9.7 to to Transition gradual to abrupt 270 180 Uneven spiral grained 7.4 4.4 11.4 Transition more or less gradual Usually straight 7.9 4.3 11.9 ........ . do ......... . , .do ... 3.6 2.7 7.8 Gradual to abrupt, latewood distinct ........ . do ......... Straight Gradual to abrupt, latewood distinct Straight Mixed 35 to 190 Mixed 175 to 200 t-' 0 0") Hemlock Eastern .38 Mountain .43 Western .38 Juniper Alligator Rocky Mountain Western 60 80 40 to to 230 220 .50 100 35 .51 110 25 0.51 to to 150 30 110 25 to to 150 30 P M . , .do ... Sapwood buff to light brown latewood with a roseate or reddish-brown tinge. Heartwood not distinct. Wood wl1itish to light yellowish-brown. Late wood with a roseate, purplish or reddish­ brown tinge . ...... . do ....... White sapwood and light red-brown heartwood. ....... do ....... White sapwood and light red-brown heartwood. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Larch, Western Specific Green gravity moisture (green content volume and SapHeartovendry wood wood weight) .48 Pet Pel. 120 40 to to 130 70 Pine Digger Eastern white ~ Permeability I Sapwood Heart­ wood Shrinkage green to ovendry Tangen- Radial tial Pet P Pet 150 Mixed to 70 UNITED STATES SOFTWOODs-continued R 8.1 4.2 13.2 Conspicuous abrupt changes springwood to summerwood. More or less abrupt P M 6.0 2.3 8.2 Gradual transition P M 6.5 3.4 10.4 Abrupt transition 6.7 4.4 210 ..;J .39 105 Jeffrey .37 100 Knobcone P M-R 9.9 More or less abrupt Abrupt transition Limber .37 Mixed 68 P M-R 5.1 2.4 8.2 Gradual transition Loblolly .47 80 30 P M to 7.4 to 4.8 12.3 Abrupt transition 140 40 150 35 P to R to 6.7 4.5 11.5 More or less abrupt 175 80 Lodgepole 0.38 Color of sapwood and heartwood Pet 0 Jack Grain Volu­ metric P .34 Contrast in density from springwood to summerwood ... do ... Whitish sapwood and russet or reddish-brown heartwood. Usually Sapwood nearly white. straight Heartwood dark yellow-brown often tinged with red. ... do ... Sapwood nearly white to pale yellowish-white. Heartwood cream colored to light brown or reddish-brown turning darker on exposure. ... do ... Sapwood nearly white. Heartwood light orange to light brown. ... do ... Sapwood nearly white to pale yellowish. Heartwood yellowish to light reddish or orange­ brown. ... do ... White sapwood. Heartwood pale yellow-brown. ... do ... Sapwood pale yellow. Heartwood cream to light brown. ... do ... Sapwood nearly white to yellowish or orange­ white or pale yellow. Heartwood shades of yellow and orange to reddish-brown or light brown. Usually Sapwood nearly white to straight pale yellow. Heartwood light yellow to pale yellowish-brown. Common name ~-., ~-- .-­ ~- Pet Permeability Sapwood -~.--~.--- 1 Shrinkage green to ovendry Heart- . wood Tang(Jn- Radial tial Contrast in density from springwood to summerwood . " _ ~ ~ ' o - , . " - . . _ . . _ _ _ ....... ~ . - ~ - ... _ _ . ._ _._ _ ~ ..._ _._ . _ _ ..• ~ ~ - . • ._ _ _........ - -... ......... _ _ ~ .. _ _ _ _ ~ "'_ _ _ _ _ _ _ _ e _ _ _ _ Green Specific moisture gravity content (green volume' Sap- Heartand wood ovendry wood weight) -- --................. ~-,-~~. "~~ __ ~ PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued ,~ _ _ _ Grain Color of sapwood and 11Cartwood S:tpwood nearly white to yellowish or oTllnge­ white or pale yellow. Heartwood slllHles of yellow and orange to reddish-brown or light brown. Sapwood nearly white to yellowish or orange­ white to pale yellow. Heartwood shade!:! of yellow and orange to reddish-brown or light urown. , ..... ,do ....... Sapwood nearly white to pale yellowish. Heart­ wood yellowish to light recldh;h or orange-brown. Sapwood nearly white tc yellowish..Heartwood Iigh t red to orange­ hrown or reddish-brown. Sapwood white to yellow. Heartwood light orange to reddish-brown. Sapwood nearly white to yellowish orange-white or pale yellow. Heart­ woodR shades of yellow and orange to reddish­ hrown or light brown. ., ..... do ....... Sapwood white. Heart­ wood light. hrown. Volu­ metric ~-~--. Pet Pet Pel, Pet UNITIi:D STATES SOF1'WOODs--continued Pine (cont.) Longleaf ,54 70 25 to to 130 50 P M 7.5 5.1 12.2 Abrupt transition Usually straight Pitch .45 Mixed 30 P H 7.1 4.0 10.9 Abrupt transition ... do ... Pond Ponderosa .50 .38 60 120 30 P P M-R P-M 7.1 6.3 5.1 3.9 11.2 9.6 .... , .... do ......... More or less abrupt ... do ... ., .do ... ..... 0 ao Red .44 to to 150 40 40 35 P M 7.2 4.6 11.5 ........ . do ......... ... do, .. to 150 Sand .36 Mixed 45 P M-H 7.3 3.9 10.0 Abrupt transition ... do ... Shortleaf .46 70 25 P M 7.7 4.4 12.3 ........ . do ......... ... do ... to to 180 150 Mixed 66 P P M-R M-R 7.8 5.5 12.2 ........ . do ......... ., .do ... ... do ... Slash Spruce .56 .41 ........ . do ......... PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Specific Green gravity moisture (green content volume and SapHeartovendry wood wood weight) Pet Pine (cont.) Sugar Permeability Sapwood 1 Heart­ wood Pet Shrinkage green to ovendry Tangen- Radial tial Pet Pet Contrast in density from springwood to summerwood Volu­ metric Pet 0.35 140 100 P M 5.6 2.9 7.9 75 P M-R 6.8 3.4 10.9 P M-R P M Gradual transition Usually straight Abrupt transition .. . do ... ........ . do ......... " .do ... Gradual transition Straight Gradual transition Usually straight Usually abrupt .. . do ... ........ . do ......... .. . do ... Gradual transition, faint growth ring ... do ... ......... do ......... Straight 220 Table-Mountain .49 Virginia .45 Western white .36 50 to to 200 60 .37 Mixed 50 P M-R .38 135 70 P to to P-M 240 245 0 Redwood Big tree Spruce Black Mixed 150 t- Whitebark Red 5.3 4.4 2.6 2.6 11.8 6.8 M .38 130 40 Blue Engelmann Color of sapwood and heartwood UNITED STATES SOFTWOODS-continued to ~ Grain <'" ~o" .38 140 40 to to 170 50 110 30 R R R R R R 6.6 3.4 10.4 ......... do ......... ... do ... R R 7.8 3.8 11,8 ......... do ......... Usually straight 6.8 4.1 11.3 Sapwood nearly white to pale yellowish-white. Heartwood light brown to pale reddish-brown. Sapwood nearly white. Heartwood light brown. Sapwood nearly white. Heartwood light orange colored. Sapwood nearly white to pale yellowish-white. Heartwood cream colored to light brown or reddish­ brown turning darker on exposure. Nearly white sapwood. Heartwood cream to light brown. Sapwood nearly white . Narrow heartwood clear light red to deep reddish-brown . ...... . do ....... Nearly white to pale yellowish-brown lus­ trous. Heartwuod not distinct. Nearly white with occasional reddish tinge. Nearly white sapwood, heartwood nearly white with an occasional sligh t tinge of red. Nearly white to pale yellowish-brown lus­ trous. Heartwood not distinct. PHYSICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued APPENDIX III-MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER Seven mechanical properties-tension per­ pendicular to the grain, hardness, modulus of elasticity, modulus of rupture, compression parallel to the grain, compression perpendicular to the grain, and shear-are given in this Ap­ pendix. The figures for tension perpendicular are taken from green material while the others are for wood at 12 percent moisture content. Tension perpendicular is important during cut­ ting when the wood is green while the other mechanical properties are most important for use of veneer in the dry conditions. Most of the mechanical properties listed here came from the Wood Handbook. In some cases, the information is from universities or from foreign laboratories. For up-to-date Canadian and U.S. values, it is suggested the reader check American Standards for Testing Materials D 2555. MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER ~---.--. Common name Tension perpendicular to grain (green) -- --­ ...Hardness (side) ~- -~ .. - -- - ­ 12 percent moisture content ---~- Modulus of elasticity ~- ---- - ._- ..- l\lodulus of rupture .. -.~--- Compression parallel to the grainmaximum crushing strpngth -.--~----.-~- Compression perpendicular to the grainfiber stress at pro­ portional limit_..__ .. ~~-- Lb/in.2 Lb 1,000 Lb/in. 2 Lb/in. 2 Alder Nepal Red Ash Black Blue Green Oregon Pumpkin Shamel White Aspen Bigtooth Quaking Basswood American White Beech, American Birch Alaskan paper Gray Paper River Sweet Yellow Buckeye Ohio Yellow Butternut Cherry, Black Lb/in.2 ---~-- Shear parallel to grain­ maximum shearing st~ength ­ Lb'in.' Lb/in.' 440 1,080 UNITED STATES HARDWOODS 510 590 1,020 1.380 1,600 1,400 1,660 1.360 1,260 1,660 1,770 12,600 13, 7~JO 14.100 12,700 11,060 12.800 15,400 5,970 6.980 7,080 6,040 5,690 760 1,420 1,310 1,250 1,460 1,570 2,030 1,910 1,790 1,720 590 850 1,290 1,200 1.160 990 860 1,320 7,410 1,160 1,950 310 230 420 350 1,430 1.180 9,100 8,400 5,300 4,250 560 370 1,080 850 280 410 1,460 8,700 4,730 370 990 1,300 1,720 14.900 7,300 1,010 2,010 380 840 760 910 1,900 1,150 1,590 13.800 9,800 12.300 7,510 4,870 5,690 830 750 600 1,420 1,340 1,210 430 430 1,470 1,260 2,170 2,010 16,900 16,600 8,540 8,170 1,080 970 2,240 1,880 430 570 490 950 1,170 1,180 1,490 7.490 8,100 12,300 4,170 5,110 7,110 360 460 690 960 1,170 1,700 390 490 590 590 770 720 200 111 8,500 9,800 5,820 MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name 12 percent moisture content Tension perpen­ dicular to grain (green) Hardness (side) Modulus of elasticity Modulus of rupture Compres­ sion parallel to the grain­ maximum crushing strength Compres­ sion perpen­ dicular to the grain­ fiber stress at pro­ portional limit Shear parallel to grain­ maximum shearing strength Lbjin.2 Lb 1,000 Lb/in. 2 Lb/in. 2 Lb/in.2 Lb/in. 2 UNITED STATES HARDWOODs-continued Cottonwood Balsam poplar (Balm of Gilead) Black Eastern Swamp Elm American Cedar Rock Slippery Winged Eucalyptus Hackberry Hickory, pecan Bitternut Nutmeg Pecan Water Hickory, true Mockernut Pignut Shagbark Shellbark Holly, American Honeylocust Koa Laurel, California Locust, Black Madrone, Pacific Magnolia Cucumbertree Southern Maple Bigleaf Black Boxelder Red Silver Sugar Oak, red Black California black Cherrybark Chestnut Laurel Northern red Nuttall Pin Scarlet 160 300 1,100 6,800 4,020 370 7~0 270 410 350 430 1,270 1,370 8,500 8,500 4,500 4,910 300 380 1,040 930 590 690 1,340 1,480 1,540 1,490 1,650 2,200 1,190 11 ,800 13,500 14,800 13,000 14,800 15,600 11,000 5,520 6,020 7,050 6,360 6,780 8,200 5,440 690 950 1,520 820 1,020 1,510 2,240 1,920 1.630 2;370 630 830 1,320 1,320 860 1,540 1,330 880 890 1,590 680 1,580 1,810 1,820 1,790 1,700 1,730 2,020 17,100 16,600 13,700 17,800 9,040 6,910 7,850 8,600 1,680 1,570 1,720 1,550 1,960 1,850 2,800 1,970 2,140 1,880 2,220 2,260 2,160 1,890 1,110 1,630 1,570 940 2,050 1,230 19,200 20,100 20,200 18,100 10,260 14,700 13,300 8,000 19,400 10,450 8,940 9,190 9,210 8,000 5,540 7,500 7,300 5,640 10,180 6,880 1,730 1,980 1,760 1,800 920 1,840 1,740 2,150 2,430 2,110 1,710 2,250 1,130 1,830 1,310 1,860 2,480 1,810 640 850 780 770 1,020 1,580 850 1,270 1,700 440 610 700 1,020 1,820 1,400 12,300 11,200 6,310 5,460 570 860 1,340 1,530 600 720 850 1,180 1,450 1,620 10,700 13,300 5,950 6,680 750 1,020 1,730 1,820 560 950 700 1,450 1,640 1,140 1,830 13,400 8,900 15,800 6,540 5,220 7,830 1,000 740 1,470 1,850 1,480 2,330 700 800 690 770 750 1,210 1,100 1,480 1,130 1,210 1,290 1,640 990 2,280 1,590 1,690 1,820 13,900 8,700 18,100 13,300 12,600 14,300 6,520 5,640 8,740 6,830 6,980 6,760 930 1,160 1,250 840 1,060 1,010 1,910 1,470 2,000 1,490 1,830 1,780 800 700 1,510 1,400 1,730 1,910 14,000 17,400 6,820 8,330 1,020 1,120 2,080 1,890 680 930 112 MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Tension perpen­ dicular to grain (green) Hardness (side) Lbjin. 2 Lb 12 percent moisture content Modulus of elasticity Modulus of rupture Compres­ sion parallel to the grainmaximum crushing strength Compres­ sion perpen­ dicular to the grain­ fiber stress at pro­ portional limit Shear parallel to grain­ maximum shearing strength 1,000 Lbjin. 2 Lbjin. 2 Lbjin. 2 Lbjin. 2 Lb/in. 2 UNITED STATES HRDWOODS-continued Oak (cont.) Shumard Southern red Water Willow Oak, white Bur Chinkapin Delta post Durand Live Oregon white Overcup Post Swamp chestnut Swamp white White Ohia Persimmon, common Sassafras Silk-oak Sugarberry Sweetgum Sweetbay Sycamore, American Tanoak Teak Tupelo Blackgum Swamp Water Walnut, Black Willow, Black Yagrumo hembra Yellow-poplar Cedar AlaskaAtlantic whiteEastern red cedar IncenseNorthern white­ Port-OrfordWestern red cedar Cypress Baldcypress Pondcypress 480 820 760 1,060 1,190 1,460 1,490 2,020 1,900 10,900 15,400 14,500 6,090 6,770 7,040 870 1,020 1,130 1,390 2,020 1,650 800 730 1,370 1,190 1,030 1,420 10,300 12,600 6,060 1,200 1,820 1,040 940 730 790 670 860 770 950 1,200 520 1,970 1,100 1,420 1,510 1,770 2,050 1,780 2,370 2,010 1,120 18,400 10,320 12,600 13,200 13,900 17,700 15,200 18,300 17,660 9,030 8,900 6,530 6,200 6,600 7,270 8,600 7,440 8,900 9,170 4,760 2,840 1,710 810 1,430 1,110 1,190 1,070 1,400 1,990 850 2,660 2,020 2,000 1,840 1,990 2,000 2,000 2,360 2,160 1,240 540 2,680 1,660 1,190 1,360 1,240 1,620 1,360 2,090 2,300 630 930 960 850 630 770 1,140 1,640 1,640 1,420 9,900 12,500 10,920 10,000 5,620 6,320 5,680 5,380 1,000 620 560 700 1,280 1,600 1,680 1,470 960 1,130 1,820 13,900 7,900 1,410 1,320 570 810 1,200 9,600 5,520 930 1,340 600 570 430 880 1,010 450 320 540 1,260 1,680 1,010 1,090 1,580 9,600 14,600 7,830 6,490 10,100 5,920 7,580 4,100 3,490 5,540 870 1,010 430 270 500 1,590 1,370 1,250 510 1,190 UNITED STATES SOFTWOODS 330 180 330 280 240 180 230 580 350 900 470 320 560 350 1,420 930 880 1,040 800 1,730 1,120 11,100 6,800 8,800 8,000 6,500 11,300 7,700 6,310 4,700 6,020 5,200 3,960 6,470 5,020 620 410 920 590 310 620 490 880 850 1,080 860 300 510 1,440 10,600 6,360 730 1,000 113 1,130 800 MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name 12 percent moisture content Tension perpen­ dicular to grain (green) Hardnrss (side) Modulus of elasticity Modulus of rupture Compres­ sion parallel to the grain­ maximum crushing strength Compres­ sion perpen­ dicular to the grain­ fiber stress at pro­ portional limit Shear parallel to grain­ maximum shearing strength Lb/in.2 Lb 1,000 Lb/in. 2 Lb/1:n. 2 Lb/in. 2 Lb/in. 2 Ld/in. 2 UNITED STATES SOFTWOODs-continued Douglas-fir Coast Interior north Interior south Interior west Fir Balsam California red Grand Noble Pacific silver Shasta red Subalpine White Hemlock Eastern Mountain Western Juniper Alligator RockY' Uountain Western Larch, Western Pine Digger Eastern white Jack Jeffrey Knobcone Limber Loblolly Lodgepole Longleaf Pitch Pond Ponderosa Red Sand Shortleaf Slash Spruce Sugar Table-Mountain Virginia Western white Whitebark Redwood Big tree 300 340 250 290 710 600 510 660 1,950 1,790 1,490 1,820 12,400 13,100 11,900 12,600 7,240 6,900 6,220 7,440 800 770 740 760 1,130 1,400 1,510 1,290 180 380 240 230 240 400 500 490 410 430 1,230 1,490 1,570 1,720 1,720 7,600 10,400 8,800 10,700 10,600 4,530 5,470 5,290 6,100 6,530 300 610 500 520 450 710 1,050 910 1,050 1,180 300 400 480 900 1,490 7,100 9,800 4,330 5,810 490 530 1,020 1,100 230 330 290 500 740 540 1,200 1,320 1,640 8,900 11,200 11,300 5,410 6,840 7,110 650 1,030 550 1,060 1,230 1,250 1,160 650 720 6,700 8,310 4,120 5,340 1,380 890 1,042 1,065 330 830 1,870 13,100 7,640 930 1,360 250 360 260 380 570 500 1,240 1,350 1,240 8,600 9,900 9,300 4,800 5,660 5,530 440 580 790 900 1,170 1,210 270 260 220 330 280 280 310 300 380 320 400 270 320 400 260 430 690 480 870 620 740 460 560 730 590 1,010 660 380 660 740 370 1,170 1,800 1,340 1,990 1,430 1,750 1,290 1,630 1,410 1,760 2,060 1,230 1,200 1,550 1,520 1,510 9,100 12,800 9,400 14,700 10,800 11,600 9,400 11,000 11,600 12,800 15,900 10,400 8,000 11,600 13,000 9,500 5,290 7,080 5,370 8,440 5,940 7,540 5,320 6,070 6,920 7,070 9,100 5,650 4,770 6,830 6,710 5,620 580 800 610 960 1,010 1,120 580 600 1,030 810 1,020 730 480 980 910 440 800 1,370 880 1,500 1,360 1,380 1,130 1,210 1,100 1,310 1,730 1,490 1,050 1,200 1,350 850 260 480 1,340 10,000 6,150 700 940 114 MECHANICAL PROPERTIES OF U.S. WOODS FOR VENEER-continued Common name Tension perpen­ dicular to grain (green) Hardness (side) Lb/in.' Lb 12 percent moisture content Moduius of elasticity Modulus of rupture Cor.:pres­ sion parallel to the grain­ maximum crushing strength Compres­ sion perpen­ dicular to the grain­ fiber stress at pro­ portional limit Shear parallel to grain­ maximum shearing strength 1,000 Lb/in.' Lb/in.' Lb/in? Lb/in? Lb/in? UNITED STATES SOFTWOODs-continued Spruce Black Blue Engelmann Red Sitka White Tamarack Yew, Pacific 100 520 1,530 10,300 5,320 530 1,030 240 220 250 220 260 450 390 490 510 480 590 1,600 1,300 1,520 1,570 1,340 1,640 1,350 9,300 10,200 10,200 9.800 11,600 15,200 4,480 5,890 5,610 5,470 7.160 8,100 410 470 580 460 800 2,110 1,200 1,080 1,150 1,080 1,280 2,230 -~--.-- 115 ---­ APPENDIX IV-SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER Ease of bark removal is based on fall-cut wood debarked by machine. The conditioning temperatures are those sug­ gested for cutting veneer about liS inch thick. The l'ecommended temperatures for rotary cut­ ting take into account the tendency of the species to develop splits at the ends of the bolts during heating, For slicing, the recommended temperature will often be 10° to 20° F higher than for peeling because splitdng is less of a problem when heating flitches for slicing. The last columns are rated on an A, B, and C scale. A indicates that the specific property i:; basically favorable for use as veneer and C indicates that the particular property may be a problem in utilizing the species for veneer. For example, an A rating for log splitting due to heating indicates the species is little af­ fected by heating while a C rating indicates that log end splits are a major problem with this species. The A, B, and C ratings for drying times are comparative. The time required to dry veneer varies widely with species and with the type of dryer being used. For this reason, rather than give specific times for a specific dryer, drying times are given in comparison with other species-yellow birch for hardwood ve­ neer and Douglas-fir for softwood veneer. Yellow birch was selected as "typical" for hardwood veneer because this is a well-known veneer species and one on which FPL had much drying data. Besides, the sapwood and heart­ wood of yellow birch take about the same time to dry. Our data show that no other hardwoods dry much faster than yellow birch. In contrast, several hardwood species require considerably longer drying time than yellow birch. So drying time ratings for hardwoods are either B or C. For softwoods, the comparison is based on the drying of sapwood or heartwood of Douglas­ fir. The sapwood of Douglas-fir takes signifi­ cantly longer drying time than the heartwood. The quality and recovery of veneer from all species is sensitive to the setting of the knife and pressure bar. However, acceptable veneer can be cut from some species with a wider range of settings than can be tolerated by other species. An A rating for sensitivity to settings of the knife and pressure bar indicates the species tolerates a wide latitude in machine setting; a C rating indicates the species cuts well only within a narrow range of machine settings. Under defects in drying, an A rating means a species is relatively free of the characteristics listed, while a C rating means the veneer from the species is subject to this particular drying defect. 116 ... Common name SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER 1 Ease of bark removal by machine 2 Suggested conditioning temperature Rotary Sliced of OF Aggra­ vation of log split­ ting due to heating Sensitivity to setting ofKnife Drying time Defects in drying Sapwood Heart­ wood Buckle Splits Col­ lapse Pres­ sure bar UNITED STATES HARDWOODS Alder Nepal Red Ash Black Blue Green Oregon Pumpkin Shamel White Aspen Bigtooth Quaking Basswood American white Beech, American Birch Alaskan paper Gray Paper River Sweet Yellow Buckeye Ohio Yellow Butternut Cherry, Black Cottonwood Balsam poplar Black Eastern Swamp Elm American Cedar Rock Slippery Winged Eucalyptus Hackberry Hickory, pecan Bitternut Nutmeg Pecan Water Hickory, true Mockernut Pignut Shagbark Shellbark 1 2 100-140 80-140 140-160 120-160 A B A A A A B B B B A A A A A A 2 2 2 2 2 2 2 120-140 140-160 140-160 140-160 140-160 140-160 140-160 140-160 160-180 160-180 160-180 160-180 170-180 160-180 B B B B B B A A B B A B B B B B B B B B B B A 1 1 40-70 40-70 40-70 40-70 A A B B A A C C C C B B A A B B 3 3 40-70 40-70 40-70 40-70 A A C C B B B C B C A A A A A A 1 160-180 180-190 B B B B B B A A-B 2 2 2 2 2 2 140-160 120-140 120-140 120-140 ].',0-160 140-160 160-180 140-160 140-160 140-160 160-180 160-180 B A A B B B B A B B B B B B B B B B B B B B A B A A B B B B B B A A A A-B A-B 1 1 2 2 40-70 40-70 70-90 120-140 40-70 40-70 100-200 150-170 A A A B C B C B B B B B C B B A A A 2 2 2 2 40-70 40-70 40-70 40-70 40-70 40-70 40-70 40-70 A A A A B B B B B B B B C C C C C C C C C C C C B B B B C C C C 2 2 2 2 120-140 160-170 160-170 120-140 B B B B B B B B B B B B C C C C C C C C C B A C C B B A A 2 2 1 160-170 140-160 120-140 150-170 190-200 190-200 180 then 150 190-200 180-200 140-160 B C A B B A B B A C C B C C B B A B A B A 3 3 3 3 160-181) 160-180 160-180 160-180 190-200 190-200 170-180 190-200 C C C C B B B C B B B B B B B C C C C C B B C B B B B B A A A A 3 3 3 3 160-180 160-180 160-180 160-180 190-200 190-200 190-200 190-200 C C C C B B B B B B B B B B B B C C C C B C B B B B B B A A A 117 A A A SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER I-continued Common name Ease of bark removal by machine 2 Suggested conditioning temperature Rotary Sliced of of Aggravation of log split­ ting due to heating Sensitivity to setting ofKnife Drying time Sap­ wood Defects in drying Heart­ v.ood Buckle Splits Col­ lapse Pres­ sure bar UNITED STATES HARDWOODs-continued Holly, American Honeylocust Koa Laurel, California Locust, Black Madrone, Pacific Magnolia Cucumbertree Southern Sweetbay Maple Bigleaf Black Boxelder Red Silver Sugar Oak, red Black California black Cherrybark Chestnut Laurel Northern red Nuttall Pin Scarlet Shumard Southern red Water Willow Oak, white Bur Chinkapin Delta post Durand Live Oregon white Overcup Post Swamp chestnut Swamp white White Ohia Persimmon, common Sassafras Silk-oak Sugarberry Sweetgum Sycamore, American 2 3 150-160 140-160 140-160 170-180 180-190 160-180 B B B A B B B B B B A B B B A A 150-160 160-180 150-160 190-200 180-190 180-190 B B B B B B B B B C C 3 3 C C C B B B B B A A A 1 1 1 70-120 70-120 70-120 120-140 120-140 120-140 A A A A A A A A A A A A A A A A A A 2 2 2 2 2 2 80-120 160-180 80-120 JOO-140 80-120 160-190 120-140 170-190 120-140 130-150 120-140 170-190 B B A B A B B B B B B B B B A B B B A-B A A C A A C C C B C C B A B A-B A B B A A A-B 2 140-160 180-200 C B B C C A B A 2 2 2 2 2 2 2 2 2 2 2 2 140-160 140-160 140-160 140-160 140-160 140-160 140-160 140-160 140-160 140-160 140-160 140-160 160-180 180-200 180-200 180-200 180-200 180-200 180-200 180-200 180-200 180-200 180-200 180-200 C C C C C C C C C C C C B B B B B B B B B B B B B B B C B B B B B B B B C C C C C C C C C C B A A B B B B B C B A B A C B C C A B C C C C C C A A A B C C 2 2 2 2 2 2 2 2 140-160 140-160 140-160 140-160 160-170 140-160 140-160 140-160 180-200 180-200 180-200 180-200 200-210 180-200 180-200 180-200 C C C C C C C C B B B B B B B B B B C C C C C A B C B B B B C C C C B C C 2 2 2 2 140-160 140-160 140-160 170-180 180-200 180-200 180-200 200-210 C C C B B B B B B B B C C C B C C B A A B B B B B B A 190-200 120-150 170-180 140-160 140-160 C C C B B B B B 2 2 1 1 150-200 100-120 150-160 120-140 120-140 B A A C C A A A A A B C C A B B 1 120-140 150-160 B A A C C C-B B B 118 B C C SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER I-continued Common name Ease of bark removal by machine 2 Suggested conditioning temperature Rotary Sliced OF OF Aggra­ vation of log split­ ting due to heating Sensitivity to setting ofKnife Drying time Sapwood Defects in drying Heart­ wood Buckle Splits Col­ lapse PresBure bar UNITED STATES HARDWOODs-continued Tanoak Teak Tupelo Blackgum Swamp Water Walnut, Black Willow, Black Yagrumo hembra Yellow-poplar 1 2 150-160 190-200 180-190 200-210 C B B A B B C C C C B A C A C A 1 1 1 2 120-140 120-140 120-140 180 then 150 40-70 50-80 70-120 150-160 150-160 150-160 180 then 150 40-70 70-80 120-140 A A A B A A A B A A A B C C C B C C C B B B B B A A A A B B B A B A A B B A B A A C B B C B B B A B B A A B A 3 2 1 UNITED STATES SOFTWOODS ". Cedar Alaska­ Atlantic white­ Eastern redcedar Incense­ Northern white­ Port-Orford­ Western redcedar Cypress Baldcypress Pondcypress Douglas-fir Coast Interior north Interior south Interior west Fir Balsam California red Grand Noble Pacific silver Shasta red Subalpine White Hemlock Eastern Mountain Western Juniper Alligator Rocky Mountain Western Larch, Western 3 120-140 140-160 B A B B B A A A 2 60-100 100-130 A A B B B A A A 2 3 140-160 70-120 160-180 70-120 B A C B B B B A C B A B A A 2 3 120-140 120-160 140-160 140-160 B B C A C B B C B A A B A B A 3 140-160 160-180 B C C B C A B B 3 3 60-120 60-120 120-140 120-140 A A B B C C C C C C A A B B A A 1 60-140 140-180 A B B B B A B A 1 60-140 140-180 A B B B B A B A 1 60-140 140-180 A B B B B A B A 1 60-140 140-180 A B B B B A B A 1 1 1 1 1 1 1 1 70-130 70-150 70-150 70-150 70-150 70-150 70-130 70-150 120-150 130-160 130-160 130-160 130-160 130-160 120-150 130-160 B B B B B B B B B B B B B B B B B B-C B-C B-C B B-C B B-C B B B B B B B C C C C B-C B-C C C C B B B B B B B B B B B B B B B B A A A A A A A A 2 2 2 120-160 120-160 120-160 160-180 160-180 160-180 B B B B B B C C C B B B C C C B B B B B B A A A 3 140-160 160-180 B C B B A B C A 3 3 3 140-160 140-160 140-150 160-180 160-180 160-180 B B B C C B B B B B B B A A C B B A C C B A A A 119 SOME PROCESSING VARIABLES OF U.S. WOODS FOR VENEER I-continued Common name Ease of bark removal by machine 2 Suggested conditioning temperature Rotary Sliced OF OF Aggravation of log split­ ting due to heating Sensitivity to setting ofKnife Drying time Sapwood Defects in drying Henrtwood Buckle Splits Col­ lapse Pres­ sure bar UNITED STATES SOFTWOODs-continued Pine Digger Eastern white Jack Jeffrey Knobcone Limber Loblolly Lodgepole Longleaf Pitch Pond Ponderosa Red Sand Shortleaf Slash Spruce Sugar TableMountain Virginia Western white Whitebark Redwood Big tree Spruce Black Blue Engelmann Red Sitka White Tamarack Yew, Pacific 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 60-140 70-120 70-120 60-140 60-140 60-120 120-160 60-140 120-160 120-160 120-160 60-140 70-120 120-160 120-160 120-160 120-140 60-120 140-180 120-140 120-140 140-180 140-180 120-140 160-180 140-180 160-180 160-180 160-180 140-180 120-140 140-180 160-180 160-180 140-160 120-140 A A A A A A A A A A A A A A A A A A B B B A B C B A B B B A B B B B B B B B B A B B B A B B C A B B B B B B B B B B B B B B A A B B B B B B B B B B B B B B B B C B C B B B B B B B B B C A B B B-C B B B B A B B B B B A B B B B-C B B B B B B B B B B B A A A A A A A A A A A A A A A 1 1 1 1 120-160 120-160 60-120 60-120 70-160 70-160 160-180 160-180 120-140 120-140 160-180 160-180 A A A A B B B B B C B B B B B B C C B B B B C C B B C B C C B B A B A A B B B B C C A A A A A A 70-120 70-120 70-120 70-120 70-120 70-120 140-160 160-180 120-140 120-140 120-140 120-140 120-140 120-140 150-160 180-200 A A A A A A B C C C C C C B B B B B B B B B B B B B B B B B B B B B B B C B B B B B B B B C B-C B B B-C B B-C B B A A A A A A A A 3 3 1 1 1 1 1 1 2 A, species property very suitable for veneer; B, intermediate; and C, less desirable for veneer. , I, species relatively easy to debark; 2, intermediate to debark; and 3, difficult to debark. I 120 APPENDIX V-EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS An A rating would indicate that the wood is resistent to development of a particular char­ acteristic even under a wide range of process­ ing conditions. A C rating indicates that the wood is highly susceptible to this particular characteristic and should indicate caution in processing to keep this specific characteristic to a minimum. Most information in Appendix V is again based on the A, B, and C scale, and expresses relative ratings. Information in the columns head "Relative freedom from veneer charac­ teristics originating in log storage and proc­ essing" involves a highly variable set of data. All these characteristics are at least to a degree under the control of the processor. EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS 1 Common name Relative freedom from veneer characteristics originating in log storage and in processing Sap stains Mold Iron stain Oxida­ tive stain Bacteria Odor Surface irregularities Extreme perme­ ability Fuzzy Shell­ ing Rough UNITED STATES HARDWOODS Alder Nepal Red Ash Black Blue Green Oregon Pumpkin Shamel White Aspen Bigtooth Quaking Basswood American White Beech, American Birch Alaskan paper Gray Paper River Sweet Yellow Buckeye Ohio Yellow Butternut Cherry, Black Cottonwood Balsam poplar Black Eastern Swamp Elm American Cedar Rock Slippery Winged B A B B B B C C B A B A B B A A A B B B B B B B B B B B B B B B B B B B A B A A A A C A A A A A A A A A A A A A A A A A A B B B B B A B B B C C A A B B C C C C A A B B B B A B B B A A B C A A C C A A A A A A B B A A A A A B B B B B B B A B B B B B B B A A B B B B A A A A A A A A B B B B A C B B C C C B B A B A A A A A A A A C C B B A A A A C A C C C C B B C C C C A A B A B C B B B C C C C A A B B B A B A A B B B B B B A B A A B A A A A A A A A A A A A A 121 B B B B B A A A A B B B A A A B B B B B B EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS I-con. Relative freedom from veneer characteristics originating in log storage and in processing Common name Sap stains Eucalyptus Hackberry Hickory, pecan Bitternut Nutmeg Pecan Water Hickory, true Mockernut Pignut Shagbark Shellbark Holly, American Honeylocust Koa Laurel, California Locust, Black Madrone, Pacific Magnolia Cucumbertree Southern Maple Bigleaf Black Boxelder Red Silver Sugar Oak, red Black California black Cherrybark Chestnut Laurel Northern red Nuttall Pin Scarlet Shumard Southern red Water Willow Oak, white Bur Chinkapin Delta post Durand Live Oregon white Overcup Post Swamp chestnut Swamp white White Ohia Persimmon, Common Sassafras Mold Iron stain Oxidative stain Surface irregularities Bacteria Fuzzy Shelling Rough B C UNITED STATES HARDWOODs-continued A A B C C A A B C C A B A B B B B B B B B B A B B B B B A A B A A A A A A A A A A A A A A A A A C C C C B B B B C A A B A A B A B B B B B B A B A A A A A A A A A A B A A B C B B A A A B B B B C B A A A A A A A A A A A A A A A A A A A A A A A A A A C C C C A B B B B A B B C C A A C C C C B B A A A A A A A A A A A C B B B B B B B B B B B B C C C C C C A A A A A A A A B B A A A A A A A A B A A A B B B A A A A A A A A A A A A A A A A A A A A A A A A A A C C C C C C C C C C C C C C C C C C C C C C C C C C A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A B-C B-C B-C B-C B-C B-C B-C A-C B-C B-C B-C B-C B-C A A A A A A A A A A A A A A A A B C C C C C C C C C C C B A C C C C C C C C C C C C B C A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A B-C B-C B-C B-C B-C B-C B-C B-C B-C B-C B-C B B A A A A A A A A A A B 122 Odor Extreme permeability A A A A EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS I-con. Common name Relative freedom from veneer characteristics originating in log storage and in processing Sap stains Mold Iron stain Oxidative stain Bacteria Odor Surface irregularities Extreme perme­ ability Fuzzy Shelling Rough UNITEI' STATES HARDWOODS-continued Silk-oak Sugarberry Sweetgum Sweetbay Sycamore, American Tanoak Teak Tupelo Black Swamp Water Walnut, Black \Villow, Black Yagrumo hembra Yellow-poplar A C C B A C C C B A A B B B B A C C C B B B B C A A B C B C B A A C B A C B C A C A A A A C B B A C C C B C B B A A A A A B C A A A A B A A A A A A A A B A A A A A A B C B A B B B A A A B C B B A A A A A A A A B A A B A A A B A B B A A B B C UNITED STATES SOFTWOODS Cedar AlaskaAtlantic whiteEastern red cedar IncenseNorthern whitePort-OrfordWestern red cedar Cypress Baldcypress Pondcypress Douglas-fir Coast Interior north Interior south Interior west Fir Balsam California red Grand Noble Pacific silver Shasta red Subalpine White Hemlock Eastern Mountain Western Juniper Alligator Rocky Mountain Western Larch, Western A C A A A A A A A A A A A A B B B C B C' B B B B B B B B B A A A A A A A A B B B B A A A A A A A A A A A A A A A A B B B B B B A A A A A A A A A A A A A A A A A A A A A A B A A A B C A C B B B B B B C C B B A A A A A A A A A A A A A A A A B B B B B B B A A A A A A A A A A A B A A A A B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B B C C C B B B B A A A A A A A A A A A A A A A A A A A B B B B B B B A B B B B B 123 B B B A B B B B A B B B B B B B B B EFFECTS OF LOG STORAGE AND PROCESSING ON VENEER CHARACTERISTICS I-con. Relative freedom from veneer characteristics originating in log storage and in processing Common name Sap stains Mold Iron stain Oxidative stain Bacteria Odor Surface irregularities Extreme permeability Fuzzy Shelling Rough A B B B B A B B B B B B A B B UNITED STATES SOFTWOODs-continued Pine Digger Eastern white Jack Jeffrey Knobcone Limber Loblolly Lodgepole Longleaf Pitch Pond Ponderosa Red Sand Shortleaf Slash Spruce Sugar Table-Mountain Virginia Western white Whitebark Redwood Big tree Spruce Black Blue Engelmann Red Sitka White Tamarack Yew, Pacific C B B C B B C B C C C C B C C C C B C C B B-C A A B B B B B B A B B B B B B C B C C C B B C C C C B C C B B A A B B B B B B A A A A A A A A A A A A A A A A A A A A A A A C C A A A A A A B B B B C B B A B A A A C A A A A A C A A C B B B A A A A A A A B B B B B B B B B B B B B B B B B B B B B C B B C B B C B C C C C B C C C C C C C C B A B C A B A A A A B A A A A B A A B C B A A B A A B A A A A A A A A A A A A A A A A C C C C C C B A B B A B B B A B B B B B B B B B B C C B B B B B B B A B B B B B B B B B B B B B B B B B B B B B B t A, good .......species resists development of undesirable characteristics under a wide range of operating conditions; B, species intermediate in resistance amI C, poor-specl"" susceptible to tbis undesirable development. 124 APPENDIX VI-APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. ~r~CIES FOR VARIOUS USES OF VENEER The last five columns of the Appendix VI table in a sense summarize all the data. An A rating indicates the species is well suited for the indicated product. A B rating indicates the species is moderately well suited for this prod- End Use uct, and a C rating indicates the species is gen­ erally not suited for the particular end product. In making these classifications, the following broad criteria were considered: Typical Specific Uses Desimble Veneer Qualities Construction plywood Building construction as subfloor, wall sheathing, roof sheathing, concrete forms, and overlaid panels. High stiffness and strength, moderate weight, and readily glued Decorative face veneer Prefinished decorative wall panels, furniture, flush doors, kitchen cabinets, and case goods Attractive figure and color, moderately hard, and readily glued Inner plies for decorative panels Inner plies for prefinished wall panels, furniture, flush doors, kitchen cabinets, and case goods Low weight, low shrinkage, straight grain, fine uniform grain, and easily glued Container veneer and plywood Wirebound boxes, bushel baskets, paper-overlaid veneer, cleated panel boxes, and plywood-sheathed crates High in stiffness, shock resistance, and resistance to splitting, light color, free from odor and taste, and moderate in weight In some instances additional end uses and comments are listed under "other." 125 APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER Common name Figure of veneer Clear ve­ neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Relative suitability for- 2 Con­ strue­ tion ply­ wood Decor­ ative face veneer Inner plies of decor­ ative panels Con­ tainer veneer and ply­ wood Other UNITED STATES HARDWOODS Alder Nepal Red Ash Black Blue Green Oregon Pumpkin Shamel White Aspen Bigtooth Quaking Basswood American White Beech, American Birch Alaskan paper Faint growth ring. Large rays slightly darker than back­ ground ......... do ........ . Scattered large flakes from wood rays C B A-B A Occasional large flakes C B B B Conspicuous growth ring, occasional burls and cross figure ......... do ........ . ......... do ........ . ......... do ........ . ......... do ........ . Pronounced parabolas from the wide growth rings. Occa­ sional pin knots Conspicuous growth ring, occasional burls and cross fig­ ure Distinct not conspic­ uous growth ring, occasional burl B A B A . ........ do ........ . ........ . do ........ . . ........ do ........ . . ........ do ........ . Distinct stripe [rom growth rings. Faint crossbar B B A A A B B B B Distinct not conspic­ uous growth ring, occasional burl B Faint growth ring B B C B A C B A A A B A B A B A Occasional cross figure, silky luster C B A A ......... do ....... . . ........ do ....... . C B A A A A B Faint growth ring ......... do ........ . Faint g owth ring Plain, fine texture . ........ do ........ . Numerous small flakes up to 1/8 inch in height C C C B B A A C A A A C Faint growth ring pat­ tern. Slow grown. Many knots and burls Distinct not conspic­ uous growth ring, occasionally wavy ......... do ...•..... ......... do ........ . ......... do ........ . ......... do ........ . Too small to quarter­ slice B A-B B B B B B B B B B B B B B A A-B Gray C Paper River Sweet Yellow Buckeye Ohio B A A Yellow Butternut C C C B Generally plain. Occa­ sionally wavy C . ........ do ........ . . .....•.. do ........ . . ........ do ........ . . ........ do ........ . n A-B 13 B B B A A B B B B Faint growth ring, close grain Plain C C A B ...•..... do ........ . Faint to moderate growth ring, very lustrous ......... do ........ . Plain; the flgure is due to color and luster c C A A n 126 C C c Underlay­ ment plywood .... do .... Plywood flooring APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER-continued Common name Clear Figure of veneer ve­ neer I Rotary- and flat-sliced Quarter- and rift-sliced Construc­ tion ply wood UNITED STATES HARDWOODs-continued Faint growth ring, oc- Light colored small B casional burl, pin ray flecks, satiny knots, and gum luster spots common Relative suitability for- 2 Decorative face veneer Inner plies of decor­ ative panels Container veneer and ply wood A B A A A Cherry, Black B Cottonwood Balsam poplar Black Eastern Swamp Elm American B B B B Faint growth ring ......... do ......... ......... do ......... ......... do ......... Plain . ........ do ......... . ........ do ......... . ........ do ......... C C C C B C C B B B B B A A B Distinct growth ring with fine wavy pat­ tern within each ring ........ . do ......... Conspicuous growth ring with fine wavy pattern within each ring ......... do ......... Faint growth ring stripe B A B A ......... do ......... Faint growth ring stripe B B A A C C A A Distinct growth ring stripe Faint growth ring stripe B A B A B A C A Ribbon grain. Occasional crosshar. Many pin knots Distinct not conspicuous growth stripe, fine sparkle from small rays B A-B C B B A-B C A Distinct not cons picuous growth ring, almost always straight grain ........ . do ..•...... ........ . do ......... ........ . do ......... Faint growth rings, fine rays, occasional dark stripes B A C B ......... do ......... ......... do ......... ......... do ......... B B B A A A C C C B B B ........ . do ......... ........ . do ......... ........ . do ......... ......•. . do ......... Very close grain, almost no visible pat­ tern Conspicuous growth ring ......... do ......... ......... do ......... ......... do ........ .....•... do ......... Very plain uniform texture B B B B C A A A A A C C C C C B B B B C Distinct not conspicuous growth ring, occasional mild cross figure Curly, wavy grain, fiddle-back dark streaks MixtUre of plain and highly figured due to mottle, stumps, and burls C A C B B-C A B B-C C A C C Cedar Rock B B Slippery B Winged B Eucalyptus B Hackberry B Hickory, pecan Bitternut C Distinct growth ring with fine wavy pat­ tern within each ring Faint growth patterns. Occasional crossbar. Many pin knots Conspicuous growth ring Nutmeg Pecan Water Hickory, true Mockernut Pignut Shagbark Shellbark Holly, American C C C Honeylocust A Koa A Irregular grain, dark streaks Laurel, California C Faint growth ring, occasional burl or blisters C C C C C 127 Other APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER-continued Common name Figure of veneer Clear ve­ neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Relative suitability Construc­ don ply wood for~ Decorative face veneer Inner plies of decor­ ative panels Container veneer and ply wood UNITED STATES HARDWOODs-continued Distinct not conspic­ uous growth ring C B C B Bland figure is limited to color changes in the heartwood C A C B Faint growth ring ......... do ......... Plain . ........ do ......... B B C C A A A A Faint growth ring, oc­ casional burls, blister, curly, and quilted Faint growth ring, occasionally curly, wavy, birdseye Faint growth ring, close grain like the maples Faint growth ring, occasionally curly or wavy, often with pith flecks ....•.... do ......•.. Faint growth ring, oc­ casionallY curly, fiddle-back, birds­ eye, wavy Most plain, occasion­ nally curly and wavy C A B A Most plain, occasionally curly and wavy, small dark rays Plain B A B A B B C B Most plain, occasionally curly and wavy, small dark rays B B A A . ........ do ......... ......... do ......... C B B A A B A A C Conspicuous growth ring, rotary-cut veneer has a watery figure with great contrast B A B B C B B C B B B B B B B B B B B B B B A A A B B B B A A B B B C C ......... do ......... ......... do ......... ..•...... do ......... ......... do ........ .do ......... ......... do ......... ......... do ......... ......•.. do .... ." .. ........ . do .. , ...... ......... do ......... ......... do ......... ......... do ......... Pronounced flake on the true quarter and a narrow flake when rift cut; distinct not conspicuous growth ring stripe . ........ do ......... . ........ do ......... . ........ do ......... • ........ do ......... . ........ do .•....... . ........ do ......... . ........ do ......... . ........ do ......... . ........ do .•....... . ......•• do ....•.... . ........ do ......... . ........ do ......... B B C B B B C B B B B B B B B B B B B B B B B ......... do ......... ........ ,do......•.. ....... , .do ......... ......... do ......... . ........ do ......... . ........ do ......... . ........ do ......... . ..•..... do ......... B B B B B B B C B B B B B B Locust, Black C Madrone, Pacific B Distinct growth ring, dark streaks associated with borer holes Faint growth ring, close grain, figure due to pigment changes in heart­ wood A A B Magnolia Cucumbertree Southern Maple Bigleaf Black A Boxelder C Red B Silver Sugar B Oak, red Black California black Cherrybark Chestnut Laurel Northern red Nuttall Pin Scarlet Shumard Southern red Water Willow Oak, white Bur Chinkapin Delta post Durand A C 128 A A A A B B A A C C Other APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER-continued Common name Clear Figure of veneer ve­ neer I Rotary- and flat-sliced Quarter- and rift-sliced Relative suitability for--2 Construction ply wood Decorative face veneer Inner plies of decorative panels Container veneer and ply wood C C B B C C B B B B B B B B B B A A A B C C B B B C B B B B B B UNITED STATES HARDWOODS-continued Oak, white (cont.) Live Oregon white C C Moderate growth ring Conspicuous growth ring, rotary-cut veneer has a watery figure with great contrast Overcup Post Swamp chestnut Swamp white White Ohia B C B B B B ......... do .•....... ......... do ......... ......... do ......... ......... do ......... ......... do ......... Faint growth ring pattern. Occasional burls Persimmon, common C Distinct not conspicuous growth ring Occasional ribbon due to interlocked grain C A-B C B Pronounced growth ring Faint growth ring pattern Distinct not conspicuous growth ring Moderate-sized ray flakes lead to the name "Iacewood" Distinct not conspicuous growth stripe, fine sparkle from small rays Plain Distinct not pronounced ribbon oc­ casionally irregular darker streaks C B C B B A B B B B C A B B C B A B A A B A B A B B C B B A n B B B B A B B B B B A B B B A A B Sassafras Silk-oak Other A Sugarberry Conspicuous growth ring Sweetbay Sweetgum A A Faint growth ring Faint growth ring, occasionally irregular darker streaks Sycamore, American B Faint growth ring Tanoak B Plain, occasional burls Teak A Moderate growth rings, dark irregular streaks, occasional burls Tupelo Black A Faint growth ring Swamp Water Walnut, Black A A B '" Pronounced ray flakes Pronounced flake on the true quarter and a narrow flake when rift cut; distinct not conspicuous growth ring stripe . ........ do ......... . ........ do ......... . ........ do ......... . ........ do ......... ......... do ......... Poorly defined ribbon grain Pronounced reddish flakes up to 1/4 inch in height Inconspicuous wood rays and occasional burls Faint growth stripe, dark irregular streaks, sometimes mottled, fiddle­ back or curly grain Distinct not pronounced ribbon, low luster ........ . do ......... .....•.. ,do., ....... ...•. , ... do ......... ......... do, ..•.... , Distinct not conspicInconspicuous growth uous growth ring, stripe, occasional occasional wavy and burl, crotch, curly cross figure 129 Face for plywood flooring Laminated golf club heads APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER-continued Common name Figure of veneer Clear ve­ neer I Rotary- and flat-sliced Quarter- and rift-sliced Construction ply wood Relative suitability for-2 Decorative face veneer Inner plies of decorative panels Container veneer and ply wood Other UNITED STATES HARDWOODs-continued Willow, Black Yagrumo hembra B A Yellow-poplar A Faint growth ring Plain, moderate-sized vessels Faint growth ring Plain, fine texture Plain C C B-C C B B-C B B Plain B B A A Toy air­ planes UNITED STATES SOFTWOODS Cedar Alaska- B Faint growth ring None B B A A C None C B A A Faint growth rings. Spike knots ineluded sapwood C A B C Incense- C Distinct, not conspicuous growth ring Distinct growth ring, many knots, streaks of white sapwood alternating with purple-red to dark red heartwood Faint growth ring Northern white Port-OrfordWestern red cedar C A ......... do ......... ......... do ......... B Atlantic white Eastern red cedar Cypress Baldcypress Pondcypress Douglas-fir Coast Interior north interior south Interior west Fir Balsam B-C Faint growth ring stripe . ........ do ......... ......... do ......... B-C B B B B-C B B B B A B A Distinct, not conspicuous growth ring ......... do ......... A-B A B-C B B Conspicuous irregular growth ring A-B A B A B ........ . do ......... Distinct, not conspicuous growth ring stripe ......... do ......... B A B A Distinct, not conspicuous growth ring stripe ... , ..... do., ...... , ......... do ......... ......... do ......... A B-C B A-B A B A B-C B-C B-C B B B A-B A-B A-B Faint growth ring stripe Distinct, not conspicuous growth ring stripe ......... do., ...•... ......... do ......... Faint growth ring stripe Distinct, not cons picuous growth ring stripe ......... do ......... B-C C C A A-B C B-C A A-B A-B A-B C C C B-C B-C B-C A A A A-B C B-C A B-C C C A A-B Conspicuous growth ring B B B ......... do ......... ........ . do ......... ... , ... , .do ... , ..... C Distinct, not conspicuous growth ring Conspicuous growth ring California red B-C Grand Noble Pacific silver C B C ......... do ......•.. ......... do ......... ......... do ......... Shasta red B-C ......... do ......... Subalpine C Conspicuous growth ring 130 Small boat parts Cedar chests Decorative knotty faces and etched veneer APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER-continued Common name Clear Figure of veneer ve­ neer 1 Rotary- and flat-sliced Quarter- and rift-sliced Construc­ tion ply wood Relative suitability for-' Decorative face veneer Inner plies of decor­ ative panels Container veneer and ply wood Other UNITED STATES SOFTWOODS-continued White Hemlock Eastern C ......... do ......... . ........ do ......... A-B C B-C A C Distinct, not conspicuous growth ring ......... do ......... ......... do ......... Faint growth ring stripe . ........ do ....... ,. ......... do ........ , B-C C B-C A-B B A-B C C B B A A C Too small to quarter­ slice C C C C Rocky Mountain Western Larch, Western Distinct growth ring, many knots, mixed white sapwood and light red-brown heartwood C C B ... , ..... do ......... ......... do ......... Conspicuous growth ring C C A C C B C C C C C B Pine Digger ......... do ......... ......... do ......... Distinct, not conspic­ uous growth ring stripe C Distinct, not conspic­ uous growth ring Faint growth ring Faint growth ring stripe None B-C C C B B-C A-B B A Distinct, not conspicuous growth ring ......... do ......... ......... do ......... Faint growth ring Conspicuous growth ring Faint growth ring stripe ......... do ......... ......... do ......... None Distinct, not conspic­ uous growth ring stripe Faint growth ring stripe B-C C C B B B-C B-C A A C C C B C C C A A A B B B C A A C C B B-C B B C C A C C B B B A B B C A B-C C C B A A B-C B-C B-C C C C A C C C C B C B B B A B Mountain Western Juniper Alligator C B Eastern white B Jack C Jeffrey Knobcone Limber Loblolly B C C B Lodgepole C Longleaf B Pitch Pond Ponderosa C B B Red B Sand B Shortleaf Slash Spruce Sugar Table-Mountain B B B A C Distinct, not conspic­ uous growth ring; faint "pocked" ap­ pearance Conspicuous growth ring Distinct, not conspic­ uous growth ring stripe ......... do ......... ......... do ......... ...... .. do ......... •........ do ......... Distinct, not conspicDistinct, not conspic­ uous growth ring uous growth ring stripe ....•.... do ...... , .. Faint growth ring stripe Conspicuous growth Distinct, not conspic­ ring uous growth ring stripe ......... do ...... , .. ......... do ......... ......... do ......... ......... do ......... ......... do ......... .... , .... do ...... , .. Faint growth ring None Conspicuous growth Distinct, not cOllspic­ ring uous growth ring stripe 131 Decorative knotty faces Decorative knotty faces APPEARANCE AND SUITABILITY OF INDIVIDUAL U.S. SPECIES FOR VARIOUS USES OF VENEER-continued Common name Figure of veneer Clear ve­ neer 1 Rotary- and fiat-sliced Quarter- and rift-sliced Relative suitability Construction ply wood for~ Decorative face veneer Inner plies of decorative panels Container veneer and ply wood B-C B B-C A-B C A C B A A C B C C B A C A Other UNITED STATES SOFTWOODs-continued Virginia Western white Whitebark Redwood C A C A ......... do ......... Faint growth ring ......... do ......... Distinct, not conspicuous growth ring; occasionally wavy and burl Distinct, not conspicuous growth ring . ........ do ......... None . ........ do ......... Faint growth ring stripe; occasionally wavy and burl Faint growth ring stripe A A Big tree A Spruce Black Blue Engelmann Red Sitka C C C C B Faint growth ring ........ . do ......... •........ do ......... ........ . do ......... ......... do ......... None ......... do ......... . ........ do ......... ......... do ......... . ........ do ......... B-C B-C B B A-B C C C C B C C C C B A A A A A White Tamarack C C ........ . do ......... Conspicuous growth ring B-C A-B C B C C A B Yew, Pacific C Mild growth ring figure ......... do ......... Distinct, not cons picuous growth ring stripe Not quarter-sliced C A C B Decorative etched veneer faces Aircraft parts I An A rating indicates Veneer logs of the species tend to have a high percent of clear wood, a C rating indicates a low percent of clear wood, and a B is intermediate. 'A. indicates species is well suited for end product; B. intermediate; and C, generally not well suited for this product. 132 GLOSSARY Annual growth ring.-The layer of wood growth put on a tree during a single growing season. In the tem­ perate zone the annual growth rings of many species (e.g., oaks and pines) are readily distinguished because of differences in the cells formed during the early and late parts of the season. In some temperate zone species (black gum and sweetgum) and many tropical species, annual growth rings are not easily recognized. Bird peck.-A small hole or patch of distorted grain resulting from birds pecking through the growing cells in the tree. In shape, bird peck usually resembles a carpet tack with the point towards the bark; bird peck is usually accompanied by discoloration extending for considerable distance along the grain and to a much lesser extent across the grain. Birdseye.-Small localized areas in wood with the fibers indented and otherwise contorted to form few to many circular or elliptical figures remotely resembling birds' eyes on the tangential surface. Sometimes found in sugar maple and used for decorative purposes; rare in other hardwood species. Bolt.-(l) A short section of a tree trunk; (2) in veneer production, a short log of a length suitable for peeling in a lathe. Burl.-(l) A hard, woody outgrowth on a tree, more or less rounded in form, usually resulting from the entwined growth of a cluster of adventitious bud:>. Such burls are the source of the highly figured burl veneers used for purely ornamental purposes. (2) In lumber or veneer, a localized severp distortion of the grain gener­ ally rounded in outline, usually resulting from over­ growth of dead branch stubs, varying from ¥! inch to several inches in diameter; frequently includes one or more clusters of several small contiguous conical proturberances, each usually having a core or pith but no appreciable amount of end grain (in tangential view) surrounding it. Cellulose.-The carbohydrate that is the principal con­ stituent of wood and forms the framework of the wood cells. Closed side.-Side of veneer not touching knife as it is peeled from log (also called tight side of veneer). Combgrain.-Veneer cut at about a 45° angle to the wood rays. The rays show as narrow, straight stripes on the face of the veneer. White oak is commonly sliced to produce combgrain face veneer. Cump1'ession wood.-Wood formed on the lower side of branches and inclined trunks of softwood trees. Com­ pression wood is identified by its relatively wide annual rings, usually eccentric, relatively large amount of summerwood, sometimes more than 50 percent of the width of the annual rings in which it occurs, and its lack of demarcation between springwood and summer­ wood in the S:lme annual rings. Compl'l.Jsion wood shrinks excessively lengthwise, as compared with normal wood. Crossband.-To place the grain of layers of wood at right angles in order to minimize shrinking and swell­ ing; also, in plywood of three or more plies, a layer of veneer whose grain direction is at right angles to that of the face plies. Crossfire.-Figure in fancy face veneer caused by the grain of the wood dipping in and out of the face of the veneer sheet. Crotch veneer.-Veneer cut from fork of tree to provide pleasing grain, figure, and contrast. Density.-As usually applied to wood of normal cellu­ lar form, density is the mass of wood substance en­ closed with the boundary surfaces of a wood-plus-voids complex having unit volume. It is variously expressed as pounds per cubic foot, kilograms per cubic meter, or grams per cubic centimeter at a specified moisture con­ tent. Diffuse-porous wood.-Certain hardwoods in which the pores tend to be uniform in size and distribution throughout each annual ring or to decrease in size slightly and gradually toward the outer border of the ring. Dubbing.-The extra heavy cut that may occur at the ends of a lathe or slicer knife when it is ground. This rounds the ends of the knife and is undesirable. Taking up slack in the parts of the grinding machine or use of short dummy knife sections at the ends of the knife during grinding will reduce or eliminate dubbing. Ea1·lywood.-The portion of the annual growth ring that is formed during the early part of the growing season. It is usually less dense and weaker mechan­ ically than latewood. Equilibrium moisture content.-The moisture content at which wood neither gains nor loses moisture when surrounded by air at a given relative humidity and temperature. Ext1·active.-Substances in wood, not an integral part of the cellular structure, that can be removed by solu­ tion in hot or cold water, ether, benzene, or other sol­ vents that do not rt'act chemically with wood compo­ nents. Fibe1' saturation point.-The stage in the drying or wetting of wood at which the cell walls are saturated and the cell cavities are free from water. It applies to an individual ceJl or group of cells, not to whole boards. It is usually taken as approximately 30 percent moisture content, based on ovendry weight. Figured veneer.-General term for decorative veneer such as from crotches, burls, and stumps. Flitch.-A portion of a log sawn on two or more faces -commonly on opposite faces, leaving two waney edges. When intended for resawing into lumber, it is resawn parallel to its original wide faces. Or, it may be sliced or sawn into veneer, in which case the resulting sheets of veneer laid together in the sequence of cutting are called a flitch. The term is loosely used. Gnm.-A comprehensive term for nonvolatile viscous plant exudates, which either dissolve or swell up in contact with water. Many substances referred to as gums, such as pine and spruce gum, are actually oleo­ resins. Hardwoods.-Generally one of the botanical groups of trees that have broad leaves in contrast to the conifers or softwoods. The terJ11 has no reference to the actual hardness of the wood. Heartwood.-The wood extending from the pith to the sapwood, the cells of which no longer participate in the life processes of the tree. Heartwood may contain phenolic compounds, gums, resins, and other materials that usually make it darker and more decay resistant than sapwood. Latewood.-The portion of the annual growth ring that is formed after the earlywood formation has ceased. It is usually denser and stronger mechanically than earlywood. 133 Lignin.-The second most abundant constituent of wood. located principally in the secondary wall and the mid­ dle lamella, which is the thin cementing layer between wood cells. Chemically it is an irregular polymer of substituted propylphenol groups, and thus no simple chemical formula can be written for it. Mineral streak.-An olive to greenish-black or brown discoloration of undetermined cause in hardwoods. Moisture content.-The amount of water contained in . the wood, usually expressed as a percentage of the weight of the ovendry wood. Mold.-A fungus growth on wood products at or near the surface and, therefore, not, typically resulting in deep discoloration. Mold discolorations are usually ash green to deep green, although black is common. Oleoresin.-A solution of resin in an essential oil that occurs in or exudes from many plants, especially soft­ woods. The oleoresin from pine is a solution of pine resin (rosin) in turpentine. Parenchyma.-Short cells having simple pits and func­ tioning primarily in the metabolism and storage of plant food materials. They remain alive longer than the tracheids, fibers, and vessel segments, sometimes for many years. Two kinds of parenchyma cells are recog­ nized-those in vertical strands, known more specific­ ally as axial parenchyma, and those in horizontal series in the rays, known as ray parenchyma. Peel.-To convert a log into veneer by rotary cutting. Pitch streaks.-A well-defined accumulation of pitch in a more or less regular streak in the wood of certain conifers. Plywood.-A composite panel or board made up of crossbanded layers of veneer only, or veneer in com­ bination with a core of lumber or of particleboard bonded with an adhesive. Generally the grain of one or more plies is roughly at right angles to the other plies. Pressure bar Fixed.-A bar on a lathe or slicer set to compress the wood just ahead of the knife edge. Roller.-Used on some lathes in place of a fixed pressure bar and performs the same function. Quarter-slicing.-A method of cutting face veneer nearly parallel to the wood rays. If the rays are large, as in oak, then they are prominent in the face veneer. Quarter-slicing also shows interlocked grain to advan­ tage in species like mahogany. Reaction wood.-Wood with more or less distinctive anatomical characters, formed typically in parts of leaning or crooked stems and in branches. In hardwoods this consists of tension wood and in softwoods of com­ pression wood. Resin.-Inflammable, water-soluble, vegetable sub­ stances secreted by certain plants or trees, and char­ acterizing the wood of many coniferous species. The term is also applied to synthetic organic products re­ lated to the natural resins. Resin ducts.-Intercellular passages that contain and transmit resinous materials. On a cut surface, they are usually inconspicuous. They may extend vertically para­ llel to the axis of the tree or at right angles to the axis and parallel to the rays. Short-grain.-Term used for cross grain as when end grain is exposed on face of veneer. Showth1·ough.-Term used when effects of defects within a panel can be seen on the face. Sliced veneer.-(See Veneer.} Softwoods.-Generally, one of the botanical groups of trees that in most cases have needlelike or scalelike leaves, the conifers; also the wood produced by such trees. The term has no reference to the actual hard­ ness of the wood. Specific gravity.-As applied to wood, the ratio of the ovendry weight of a sample to the weight of a volume of water equal to the volume of the sample at a speci­ fied moisture content (green, air-dry, or ovendry). Stain.-A discoloration in wood that may be caused by such diverse agencies as micro-organisms, metal, or chemicals. The term also applies to materials used to impart color to wood. St1'aight-grained wood.-Wood in which the fibers run parallel to the axis of the piece. Tension woo d.-A form of wood found in leaning trees of some hardwood species and chaL'acterized by the presence of gelatinous fibers and excessive longitudinal shrinkage. Tension wood fibers hold together tenaci­ ously, so that sawed surfaces usually have projecting fibers, and planed surfaces often are torn or have raised grain. Tension wood may cause warping. Texture.-A term often used interchangeably with grain. Sometimes used to combine the concepts of density and degree of contrast between springwood and summerwood. Veneer.-A thin layer or sheet of wood. Rotary-cut veneer.-Veneer cut in a lathe which rotates a log or bolt, chucked in the center, against a knife. Sawed venee1'.-Veneer produced by sawing. Sliced venee1·.-Veneer that is sliced off a log, bolt, or flitch with a knife. Veneer checks.-When wood is cut into veneer with a knife, checks often form on the side of the veneer next to the knife. In general, checks tend to lie deeper in thick veneer of dense wood than in thin veneer of low­ density wood. Also called ;':nife checks, lathe checks, and slicer checks. Veneer clipper.-Machine for cutting veneers into de­ sired sizes. 134 INDEX Abnormal wood, 15 Adventitious buds, 17, 24 Appearance, 125 Back grinding, 57 Back-roll lathe, 49 Bacterial action, 29, 121 Bark pockets, 24 Bark removal, 30, 117 Bird peck, 19, 24 Bolts for veneer, 31, 51, 68 Botanical names, 91 Box shook, 1, 125 Bucking into bolts, 31 Buckle, 3, 83, 117 Burls, 17, 24 Bushel baskets, 5, 125 Case goods, 5, 125 Checks in veneer, 11 Chucks, 49, 58 Cleated panel boxes, 5, 125 Clipping veneer, 69 Close grain, 23 Color, 10, 17, 24, 95 Common names, 91, 95 Compression parallel, 23, 111 Compression perpendicular, 23, 111 Compression wood, 15, 24 Concrete form, 4, 125 Conditioning wood, 34,117 Construction plywood, 4, 125 Container plywood, 22, 125 Conveying veneer, 69 Core, 5, 125 Cracks, quality control, 81 Crossband, 5, 125 Cutting: back cut, 34, 49 direction, 32 equipment, 45 flat-slicing, 32, 49 half-round, 32, 49 quarter-sliced, 34, 49 rift-cut, 32, 49 rotary, 32, 45 sawn, 34 slicing, 45 speed, 53 stay-log, 49 Cylindrical form, 24 Debarking, 30, 117 Decay, 24 Decorative plywood, 3, 125 Core,4,125 Crossband, 4, 125 Defects in drying, 117 Diameter effect, 40 Dimensional stability, 11, 23 Dryer: emissions, 74 fires, 86 types, 72 Drying: techniques, 29, 74 temperatures, 74 time, 38, 74, 117 veneer, 70 Eccentricity, 14, 24 Electric heating, 44 Embedded metal, 20, 24 End uses, 4, 125 Epicormic' ranches, 17, 23 Extractives, 9, 23 Extraneous cell content, 9 Faces, 4 Felling splits, 20 Figure, 11. 17,23, 34, 129 Fine texture, 23 Fire scars, 19 Flat-slicing, 32, 49 Flitches for veneer, 32, 68 Flush doors, 5, 125 Function of log grades, 13 Furniture parts, 2, 5 Generalized settings, 66 Grain effects, 8, 17,40,95 Grinding: veneer knife, 56 back grinding, 57 Growth rate, 7, 24 Growth stresses, 15 Gum, 9, 23 Gum streaks and pockets, 19 Half-round cutting, 32, 49 Handling damage, 24 Hard deposits, 11, 23 Hardness, 23, 111 Hardwoods, 2 Heat distortion, 51 Heating: benefits, 39 bolts and flitches, 31, 44 color changes, 37 decay resistance, 38 dimensional changes, 37 disadvantages, 39 drying time, 38 effects, 34 growth stresses, 37 hardness, 36 hot water, 40, 42 plasticity, 34 rate, 41 shrinkage, 38 stearn, 40, 42, 44 strength, 37 time required, 40, 41 torque, 38 variability, 40 warp, 38 Hot water heating, 42 Ideal veneer log, 12 Individual species, 91, 95, 111, 116, 121, 125 135 Industrial plywood, 4 Inner plies: 4 case goods, ·1 flush doors, 4 furniture, 5 wall panels, 4 Irregular grain, 17, 23 Kitchen cabinets, 4 Knife: angle, 48, 59 back grinding, 57 bevel, 48, 55 generalized settings, 66 grinding, 56 honing, 57 secondary bevels, 57 selection, 54 setting, 58, 117 slicer, 60 terminology, 48 wear, 55 thickness, 55 type, 54 Knots, 16, 24 Lathe: advantages, 47,49,69 back-roll, 49 cutting action, 45 dynamic equilibrium, 53 operation, 45 stay-log, 49 Log: breakdown, 31 characteristics, 24 diameter eccentricity, 14 end splits, 15, 24 grades, 13 handling damage, 20 processing, 31 requirements, 13 splits, 29, 41 storage, 29, 121 Mechanical properties, 12, 23, 111 Metal stain, 11 Mineral streak, 24 Modulus of elasticity, 23, 111 Modulus of rupture, 23, 111 Moisture content, 3, 6, 23, 34, 41, 73, 84, 95, 111 Mold, 121 Movement, undesirable: wood, 49, 51 machine parts, 49, 51 Names, 91, 95 Odor, 11, 23, 29 Oleoresin, 10 Overlaid panels, 5 Paper-overlaid veneer, 5 Parenchyma, 8, 23 Peeling techniques, 29 Permeability, 7, 23, 95 Physical properties of wood, 3, 23, 95 Pitch pockets, 24 Plywood: block flooring, 4, 125 construction, 4, 22, 125 industrial, 5, 22, 125 Plywood-sheathed crates, 5, 125 Polyphenols, 10 Prefinished panels, 5 Properties of veneer logs, 11 Pressure bar: fixed, 60, 65 generalized setting, 66 lead for lathe, 61 lead for slicer, 61 roller, 60, 65 setting, 61, 117 setting gap, 63 terminology, 48 Processing variables, 116, 121 Quality control: buckle, 83 casehardening, 86 checks or cracks, 81 collapse, 86 color, 86 honeycom b, 86 shrinkage, 86 stain, 75 veneer roughness, 79 veneer thickness, 75 Quarter-sliced, 34, 49 Requirements for veneer logs, 13 Resin, 10, 23 Resistance to splitting, 24 Retractable chucks, 50 Rift-cut, 32, 49 Ring shake, 16, 24 Roof sheathing, 4 Rotary cutting, 32, 47, 49, 87 Sawing into bolts, 31 Scars, 24 Seams, 19 Shake, 16 Shear, 2'I, 111 Shelling, 6, 8, 121 Shrinkage, 7, 23, 95 Slicer: advantages, 47, 49 dynamic equilibrium, 53 heat distortion, 53 offset, vertical face, 52 mechanism, 45 parts movement, 52 pawl & rachet, 52 stop plate, 52 wood movement, 52 yields, 87 Slicing techniques, 29, 45, 49 Species: appearance, 125 bark removal, 30 classification for pJywood, 22 density ranges, 22, 95 individual, 30, 91 log storage, 121 nomencJature, 91 processing variables, 116, 121 properties, 23 specific gravity, 25 136 \ suitability, 125 United States, 21, 25, 91, 95, 111, 116, 125 Species nomenclature, 91 Specific gravity, 3, 23, 25, 41, 42, 95 Specific uses, 125 Spindles, lathe, 50 Spinout, 38 Splits, 24, 117 Spur configuration, 50 Stains, 19, 24, 29, 121 Stay-log, 49 Steam heating, 42 Storage of logs, 29 Straight grain, 17, 23 Stresses, growth, 15 Stump pull, 20, 24 Subfloor, 4 Suitability for use, 125 Surface roughness, 121 Sweep, 24 Taper, 24 Temperature: constant, 41 final, 34, 39, 40 gradient, 40 storage, 29 total change, 40 Tension perpendicular, 111 Tension wood, 15, 24 Terminology, 48, 67 Texture, 8 Thickness, 2, 76 Timber requirement, 88 Torque, 38 Tl:'ee names, 91 Undesirable movement, 49, 51 Uniformity of thickness, 2, 76 Veneer: appearance, 125 buckle, 3, 83 characteristics, 121 checks, 11 color, 17, 24, 95 conveying and clipping, 69 cutting, 1, 4, 45 decorative face, 4, 125 dryers, 74 drying, 70 figure, 11, 17, 23, 34, 129 flitches, 32, 68 gluability, 4 hardwoods, 22, 91, 121 lathe, 49, 69 properties, 70, 95, 111 quality, 2, 4, 75 roughness, 2, 121 slicer, 49, 69 softwoods, 22, 91, 121 species, 91 stiffness, 23, 111 strength, 23, 111 thickness" 2, 76 uses, 4, 1"5 volume, 87 Veneer logs: characteristics, 13, 30 diameters, 13 form, 14 grades, 13 length, 13 properties, 13 sweep, 14 taper, 14 Veneer plant requirements, 88 Veneer yields, 87 Volume for plant, 87 Wall panels, 4, 125 Wall sheathing, 4, 125 Wax, 11,23 Wirebound boxes, 5, 125 Wood: conditioning, 34, 117 movement in cutting, 49 permeability, 7, 23, 34, 95 physical properties, 3, 95 species, 4, 22, 91 suitability for veneer, 125 temperature, 34 '* 137 us GOVERNMENT PRINTING OP'FICEt fD7B 0-245-770 ," " ", . 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