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Hardwood Record — Veneer & Panel Section 



July 10, 1919 



PLYWOOD 



For Makers of 



FURNITURE 

 CABINETS, CHAIRS 

 TABLES, DESKS 

 TRUNKS 

 MOTOR TRUCKS 

 FILING CABINETS 

 INTERIOR TRIM & 

 FIXTURES 



Made of 



QUARTERED OAK 

 MAHOGANY 

 BLACK WALNUT 

 QUARTERED GUM 

 PLAIN RED GUM 

 PLAIN OAK 

 ASH, BIRCH, ELM 

 BASSWOOD & MAPLE 



Flat or Bent Work Machined m- in Panels, With 

 or Without Part Cabinet Work Finished or in the White 



Send Us Your Specifications 



WISCONSIN CABINET & PANEL COMPANY 



NEW LONDON, WISCONSIN 



t Ct'tiluiiin! lii'Di f'lii/r -'jt 



Other hand, increasing the number of plies produces a 

 similar result. In three-ply panels warping may result from 

 even small variations in the 90 degree angle between the 

 grain of the core and the faces. 



High shrinkage may introduce undesirable stresses in a 

 structure to which the plywood is fastened as well as cause 

 internal stresses. Therefore minimum shrinkage of ply- 

 wood is important for many purposes. A knowledge of 

 the approximate shrinkage is necessary to determine the 

 possible change of dimension with changing moisture 

 content. 



The shrinkage of plywood varies with the species, the 

 ratio of ply thickness, the number of plies, and the com- 

 bination of species. The average shrinkage obtained in 

 several hundred tests on a variety of combinations of 

 species and thickness in bringing three-ply wood from the 

 soaked to the oven-dry condition was 0.45 per cent 

 parallel to the face grain and 0.67 per cent perpendicular 

 to the face grain, with the ranges of 0.2 to 1.0 per cent 

 and 0.3 to 1.2 per cent, respectively, in connection with 

 these values, it should be borne in mind that other com- 

 binations and thicknesses may extend these limits and 

 modify these results to some extent. 



In ordinary wood there is considerable variation in the 

 weight and strength of material from the average values 

 for the specifes. The probable variations of a single test 

 from the average may be as much as 20 per cent, depend- 

 ing on the property and species considered. It should be 



borne in mind that in plywood, where a large number 

 of additional factors are involved, the probable variation 

 of results may be even greater than for ordinary wood, and 

 that additional tests on plywood or changes in commer- 

 cial processes of manufacture will modify the values given 

 in Tables I and 2. 



Glue Failures Not Always Due to Glue 



Glues are often blamed for failures for which they are not 

 responsible. Tests made at the Forest Products Laboratory at 

 Madison, Wis., show that properly handled commercial glue de- 

 velops a shearing strength greater than that of most woods. 



The average glue user prepares his glue with reasonable intel- 

 ligence but commits atrocities in preparing surfaces to be glued 

 and in handling pieces after gluing. To get full strength from any 

 glue, proper surface contact is imperative. Good glue will 

 adhere fairly well even with poor surface contact. Joints of this 

 kind possess, however, inherent weakness and the added dis- 

 advantage that they are more liable to ruin through bacterial 

 action than tight joints, since the glue in them is more exposed. 



The proper application of pressure is important in all glued 

 work but doubly so in the manufacture of plywood. Securing 

 proper pressure involves keeping cauls and press in first-class con- 

 dition and using them skillfully. With the hydraulic press it is 

 easy for careless or ignorant workmen to spoil a batch of stock 

 by applying too much pressure and starving the joint. 



Plywood failure may often be traced to unevenly surfaced cores. 

 Planer work should be watched carefully and calipered frequently. 

 A low spot in a batch of cores will mean that insufficient pressure 

 will be obtained in that place and loose plywood or blisters may 

 result. 



