/yu-/^ FOREST PRODUCTS LABORATORY t FOREST SKRVK E U. S. DEPARTMENT OF AGRICULTURE VENEER CUTTING AND DRYING PROPERTIES PONDEROSA PINK Ponder OS a pine, Pinus ponderosa, is one of the most widely distributed and important of the western timber trees. It grows in every State west of the Great Plains, and in British Columbia and northern Mexico (3). — The wood of ponderosa pine varies widely in quality. The outer portions of old-growth trees are often soft, slow grown, and uniform in texture. Second - growth trees and the inner portions of old-growth trees may be knotty, resin- ous, comparatively hard, and their summerwood is markedly denser than their springwood. The sapwood, which generally is 2 to 4 inches thick, is white to pale yellow, and the heartwood is light reddish brown. The wood is moderately light in weightand generally straight grained. Occasional trees have spiral grain. High-grade ponderosa pine lumber is used principally for doors, sash, frames, paneling, and molding, while the lower grades are used for boxes, sheathing, joists, and rafters. Rotary-cut ponderosa pine veneer is made into plywood for such uses as kitchen cabinets. Sliced knotty ponderosa pine is made into plywood for use as paneling. Selection and Handling of Logs Veneer cutting tests were made on five different lots of logs obtained from various locations. Four of the shipments consisted of old-growth timber and the fifth of tree tops of second-growth timber. These logs are described in table 1. Uniformly slow growth is preferred to fast growth in veneer logs. Some of the defects observed in test logs, which should be avoided whenever possible, were decay, blue stain, large knots, and pitch streaks. Ponderosa pine is very susceptible to blue stain, and should be cut into veneer as soon as pos- sible after the tree is felled. If this is not possible, the logs should be stored under water. 1 "Underlined numbers in parentheses refer to Literature Cited at the end of the text. Rept. No. 1766-12 July 1956 • Maintained at Madison 5, Wisconsin in cooperation with the University of Wisconsin Agriculture • Madison Preparation of Logs for Cutting Ponderosa pine canbe rotary cut or sliced at room temperature (2, 6). Lab- oratory tests showed that tighter and smoother veneer canbe produced from logs and flitches that have been heated at 140° F. This is particularly true when 1/8- or 1 / 4-inch-thick veneer is cut. Ponderosa pine veneer logs or flitches conditioned in water at 140° F. should be heated for the periods shown in table 2. Lathe and Slicer Settings Settings (4) that were satisfactory for cutting veneer of various thicknesses are given in table 3. Veneer Drying As shown in table 1, the moisture content is about four times as great in ponderosa pine sapwood as in the heartwood. Because of this difference in moisture content, the sapwood veneer requires a longer drying period than the heartwood. Schedules for drying the veneer in a progressive, roller- conveyor dryer are shown in table 4. Some of the sheet ends of the rotary-cut sapwood veneer wrinkled during dry- ing. In further tests, wrinkling was prevented by overlapping the ends of the veneer sheets 1/4-inch as they were fed into the dryer (5). The sliced veneer dried flat except for some buckling around knot clusters. Some of the larger knots split during drying. In one specification, knotty western white pine flitches are limited to a knot size of 1 inch(l). It would be desirable to limit the knot size in ponderosa pine flitches. A maximum diameter of 2 inches would probably be acceptable from the technical standpoint of cutting and dry- ing the veneer. Veneer Yields When compared with the Scribner Decimal C log rule, both the rotary-cut and the flat-sliced veneer generally showed an overrun in laboratory tests. The yield of quarter-sliced veneer was about that indicated by the log scale. Veneer yields obtained under factory operating conditions, however, usually fall far short of those obtained in laboratory tests. Rept. No. 1766-12 -2- The yield of veneer from individual logs varied greatly. The Logfl from Mexico yielded 34 percent clear veneer; those from Libby, Montana, 7 1 percent clear veneer; those from Flagstaff, Arizona, 20 percent clear veneer; the log from Lincoln County , Montana, SS percent « lear veneer; and the tree tops from California, 100 percent knotty veneer. Plywood Laboratory tests and commercial experience show that ponderosa pine can be glued with protein and resin glues by the cold-press and the hot-press methods. Other tests have shown that ponderosa pine is in the group of woods that glue well with different glues under a moderately wide range of gluing conditions (7). Pitch that is sometimes encountered in ponderosa pine heartwood may cause plugging of the finishing belt. It is reported that this may be overcome by using a more open-coated paper than is used for Douglas-fir (2). Most ponderosa pine plywood is made for interior use (8). The light color and even texture of old-growth ponderosa pine make it well suited for uses such as cabinets. Knotty material makes attractive paneling when it is flat- sliced. Rept. No. 1766-12 -3- 1.2-8 Literature Cited (1) Anderson, I. V. 1948. Specifications for Knotty Western White Pine Veneer Flitches. N. Rocky Mt. For. & Range Exp. Sta. Research Note No. 68. (2) 1954. Suitability of Rocky Mountain Woods for Veneer and Plywood. Journal of Forestry 52(8): 587-591. (3) Betts, H. S. 1945. Ponderosa Pine. American Wood Series. Forest Service, U. S. Department of Agriculture. (4) Fleischer, H. O. 1949. Experiments in Rotary Veneer Cutting. For. Prod. Res. Soc. Proc. p. 137 (5) Lutz, J. F. 1955. Causes and Control of End Waviness During Drying of Veneer. Forest Products Journal. 5(2): 114. (6) Reinmuth, P. 1950. The Manufacture of Pine Veneer. For. Prod. Res. Soc. Proc. p. 332-338. (7) U. S. Department of Agriculture 1955. Wood Handbook. Agriculture Handbook No. 72, p. 234. (8) U. S. Department of Commerce 1949. Ponderosa Pine and Sugar Pine Plywood. Commercial Standard CS 157-49. Rept. No. 1766-12 -4- bO 3" O P □ -r4 IV o OS ..: p cd «H -1 ;-, o CO CD *-) 88 c_> > CD H bo cd >< u n to o • p MO 1) O a A H J3 p O P o .a •H > I cd OJ O >h U, -H £4 p cd cd x\ cd p MH O •H O Cd I o -: cd > to J) o to H U O U bO-H - cd • Hon r-l -h p cd x) O *|j 8 3 3 p s'S c3 cd O Q) o > 43 i to T3 O 0J o H M O b0 P cq cd ■H t>> CO J; O O I -3" O lf\ CO bf o u a ID > Cm O (3 O •H P Ph •M M o CO 0) « I I p H cd ta i X) O O > P< cd CO c\j i CO 3 CVJ o I CO OJ -4- II^v 3 P< I CvJ -=J-^ K> • l O I o CVJ to cd M > O 43 O P > X) P< -H cd 5 co \o l OJ H I KN m 9 « M 43 CD O -4- I m i ON o ir\ t- I o H 1 I tr\ H Cm O CD CO O bO O CO n =| 1 o E tH 5 M 43 S •p co cd > cd P -H §£ O O - H 43 cd Kept. No. 1766-12 Table 2. --Heating schedules for ponderosa pine logs and flitches in water vats Average diameter—; Vat temperature Heating time- Inches 12 24 36 8 12 16 F. LOGS 140 140 140 FLITCHES 140 140 140 Hours 7 37 80 7 16 29 1 "Average end dimension for flitches. -If steam is used in place of water, the heating times could be reduced 5 to 10 percent. Rept. No. 1766-12 Table 3. --Knife settings for cutting ponderoaa pine veneer Veneer thickness Kni 1 Pressure b a r Bevel Angle Bevel Vertical opening Horizontal opening Inch : Degrees Degrees - Minutes Degrees : Inch Inch LATHE 1/8 (0. 1250) : 21 89 • ■ 55 1/16( . 0625) 21 90 - - 15 l/20( . 0500) 21 90 - ■ 30 15 15 15 SLICER 1/4 ( . 2500) 1/8 ( . 1250) 1/16( . 0625) 20 20 20 90 - 20 90 - 20 90 - 30 12 12 12 0. 026 . 014 014 035 . 035 . 030 0. 1 10 050 . 040 . 240 . 115 . 055 —Lathe knife: Rockwell hardness 58; hollow ground 0. 002 inch. Slicer knife: Rockwell hardness 62; flat ground. Rept. No. 1766-12 UNIVERSITY OF FLORIDA 3 1262 09216 3004 Table 4. --Schedules for drying ponderosa pine veneer Veneer : Sapwood or : Temperature :Time in : Final moisture content thickness : heartwood : in dryer : dryer : Average : Range Inch :Sapwood : °F. 315 :Minutes : Percent : 8 : Percent 1/4 : 27 : 5-14 Heartwood 315 : 19 : 6 : 4-9 1/8 Sapwood 315 15 : 3 : 2-4 Heartwood 315 11 : 2 : 1-1/2 - 3 1/16 Sapwood : 255 9 5 : 4-8 Heartwood : 255 5 7 4 - 9 Rept. No. 1766-12