1.9 A SIMPLE DEVICE ECR DETECTING COMPRESSION WOOD December 1941 j-^caJ. u±s! I r-2 THIS REPORT IS ONE Of A SERIES ISSUED TO AID THE NATION'S DEEENSE EFEORT NO. 1390 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin A SIMPLE DEVICE FOR DETECTING COMPRESSION WOOD- A simple device that facilitates the detection of compression wood in lumber from Sitka spruce and other coniferous species has re- cently been developed by the Forest Products Laboratory. Consisting of a simple box containing an electric light arranged to cast its rays through an aperture, the apparatus discloses the ^respncp of compression wood, which is relatively opaque compared with translucent normal v?ood. When a thin specimen containing compression wood is placed in the- aper- ture, the compression wood blocks the passage of light much more than dees normal wood (fig. 1). Compression wood is responsible for much crook and bow in lum- ber and has mechanical properties inferior to those of normal wood. For these reasons it is particularly objectionable in lumber to be used for aircraft.— The new apparatus (fig. 2) reveals the presence of gradational forms of compression wood which hitherto have been discernible only under microscopical examination. It permits rapid examination of thin cross sections from lumber up to 4 by r 3 inches in size-J. Very pronounced com- pression wood, which is particularly objectionable, ordinarily can be detected on large transverse surfaces by its comparatively wide and eccentric annual rings containing a high percentage of summerwood. not so hard as normal summerwood nor, when dry, as dark. Compression wood con- sequently lacks the customary marked contrast between normal summerwood and springwood, arid thus has a "lifeless" appearance. It is in revealing the less pronounced gradations of compression wood, difficult to detect without a microscope, that the new apparatus is particularly helpful. The summerwood of compression wood evidently is more opaque than normal summerwood because the microscopically discontinuous structure of the secondary cell wall of the summerwood tracheids dissi- pates the light. Normal summerwood does not have the microscopic checks and striations in the secondary cell wall which characterize compression wood. -This mimeograph is one of a series of progress reports issued by the Forest Products Laboratory to aid the Nation's defense effort. 2 -Structure, Occurrence, and Properties of Compression 7,'ood, by ]'. Y. Pillow and R. F. Luxford. U.S.D.A. Tech. Bui. r -k6 , illus. 19^7- 2X New Method for Detecting Compression Wood, by Maxon Y. Pillow. Jour. Forestry 39(4) : 33S-3S7 , April 19UI. Mimeo. No. 139C Variations in moisture content of - r ooi pxroeax to have little effect on this method of detecting compression "vocd. Pitch-so- ood, on tne other hand, is highly translucent regardless of whether it con- tains compression wood. It is tnerefore not -ell adapted for this i Some ritch is found in Douglas-fir, but Sitka srurc^ in little it. Surfaces of samples cut with a circular cut-off saw or ordin- ary hand saw, provided it is reasonably sharp, ar< suitable for t r -st provided the end grain surfaces are parallel. Sar.de^ surfac 3 are unsatisfactory because in sanding the cell cavities b son filled with particles of wood nnd sand which destroy the trenblucence of nor wood, and, hence, its contrast to comoression wood when examir . specimens should, be cut, before fabrication, fror. ach ^i^ce of lumber suspected of containing compression rood and examined in the li ox. Cross sections ^l'^2 inch thick provided the most satisfactor ns in Laboratory tests. Making the Aooaratus lie direct sunlight or a powerful flashlight sometime-, rives useful results fo^ thin specimens, for accurate inspections t Laboratory ,-poaratus is needed. Working dra^in -3 she" its construction features (fig. 3)' A 75 -, watt electric light is strong enough to give good penetration. This box should be used in a dark room. Its exterior grooves for the specimen slides are painted black to reduce reflection of extraneous light. If the device is us-^d in ordinary room li- v r.t , a simple fiberboard viewing device can be made as indie ' Ln figure U, and held together with gummed paper. A wood viewing device, fitted with srecir.en slides at one • and used with an ordinary flashlight, electric light bulb, or direct sunlight, has also been designed. Working drawings for it are she in figure 5« The Laboratory model takes only specimens up to !! inches wide, but dimensions of the slide can be varied for larger srec:- 1390 ' - ■ Fig. 1. Cross sections of wood which were photo- graphed by transmitted light. Above, normal wood showing translucence , and below, compression wood interspersed with normal wood showing location of compression wood by its opaque summerwood. Zlt-38054-F -p q •H -P O CD -P • u o Cm CO -H 3 -H -P as t3 U V as -P (X -P aS 6 d 1 -p >> ^i T3 O O W a o •H CO w CD fa a, I o o o -p as u o jo CO -p o O ■ o o CJ •H (X4 -0- -0--0- --0- A'dia. ventilation holes "i? 0—0—0 i DIA. HOLE FOR ELECTRIC CORD 0/ _i_ SIDE VIEW END VIEW Fig. 3* Working drawings of a wood box to "be used to detect compression wood by transmitted light. ZM-39767-F ino r— SIDE VIEW FRONT VIEW Fig. 5. Working drawings of a wood "box for holding and examining cross sections of wood to detect comp- zk 3976s f pre s si on wood "by transmitted light. UNIVERSITY OF / „.J»lllli 267 3 1262 08866 6267 /