46 



Hardwood Record — Veneer & Panel Section 



March 25, 1921 



Rotary Cut 



Northern 

 Veneers 



Members of 

 Maple Flooring 

 Manufacturers' 

 Association 



■OURNITURE manufacturers and factory buyers who insist on 

 ^ having high quality veneers should send us their orders. We 

 are specialists in Northern Veneers. u , , ^ j 



We also manufacture Northern Pine. Spruce, Hemlock, Cedar 

 Posts and Poles, Lath and Shingles, which we ship in straight 

 cars and cargoes or mixed with our "Peerless Brand" Rock 

 Maple, Beech or Birch Flooring. Gi-I Our Frucs 



The Northwestern Cooperage & Lumber Company 



Chicago Offices: 812 Monadnock Block 



GLADSTONE, MICH. 



The Mayflower of Mahogany 



p\CTOBER 17, 1906, 

 ^^The Mengel Co. 

 shipped on the S. S. 

 "CORINTH" the first 

 complete cargo of ma- 

 hogany logs ever im- 

 ported from Africa into 

 the United States. 



Ill Ffel^lGllL COMEWIY 



INCORPORATED 



Louisville. Ky. 



THE PAST AND PRESENT IN MAHOGANY 



!ircuhtion 



Smoke-Making Device for Testing the Circul 



in Kilns 



Watching smoke travel through the piles of lumber is the best 

 method of testing the circulation in a dry kiln. The smoke may 

 be made by burning punksticks, tobacco or rope. Some fire risk, 

 however, attends the use of any of these. Furthermore, the smoke 

 has a temperature higher than that of the air in the kiln and tends 

 to rise of its own accord before following the air currents. 



A device w^hich produces a fireless chemical smoke is used for 

 testing circulation in the kilns at the Forest Products Laboratory, 

 Madison, Wisconsin. This device is easily made by anyone and 

 requires only the follow^ing materials: some short, thin pieces of 

 board; 2 small, wide-mouthed bottles, ink bottles will do; 3 feet 

 of 3/16-inch rubber tubing; 6 inches of 1/8-inch glass tubing; a 



two-hole rubber stopper to fit one of the bottles; some concen- 

 trated ammonium hydroxide and some hydrochloric acid. The 

 accompanying sketch suggests how the apparatus may be con- 

 structed. 



To use the apparatus, pour a small amount of the chemicals 

 into the bottles as shown. Blowing through the tube A will 

 cause a dense white smoke to issue from the bottle containing 

 ammonia. This device may be carried into a kiln without danger 

 of fire, and the smoke will be found to follow air currents without 

 any tendency of its own to rise or fall. 



Properties of Ordinary Wood Compared with 

 Plywood 



Wood, as is well known, is a nonhomogeneous material, with 

 widely different properties in the various directions relative to the 

 grain. This difference must be recognized in all wood construc- 

 tion, and the size and form of parts and placement of wood should 

 be such as to utilize to the best advantage the difference in prop- 

 erties along and across the grain. Were wood a homogeneous 

 material such as cast iron, having the same strength properties 

 in all directions that it has parallel to the grain, it would be unex- 

 celled for all structural parts where strength with small weight is 

 desired. 



The Forest Products Laboratory has found that the tensile 

 strength of wood may be 20 times as high parallel to the grain as 

 perpendicular to the grain, and its modulus of elasticity from 1 5 

 to 20 times as high. In the case of shear the strength is reversed, 

 the shearing strength perpendicular to the grain being much 

 greater than parallel to the grain. The low parallel-to-the-grain 

 shearing strength makes the utilization of the tensile strength of 

 w^ood along the grain difficult, since failure w^ill usually occur 

 through shear at the fastening before the maximum tensile strength 

 of the member is reached. 



The large shrinkage of vt'ood across the grain with changing 

 moisture content may introduce distortions in a board that decrease 

 its uses where a broad, flat surface is desired. The shrinkage from 

 the green to the oven-dry condition across the grain for a flat- 

 sawed board is about 8 per cent and for quarter-sawed board 

 about 4^/2 per cent, w^hile the shrinkage parallel to the grain is 

 practically neglible for most species. 



It is not always possible to proportion a solid plank so as to 

 develop the necessary strength in every direction and at the same 

 time utilize the full strength of the wood in all directions of the 

 grain. In such case it is the purpose of plyw^ood to meet this 

 deficiency by cross banding, which results in a redistribution of 

 the material. 



In building up plywood a step is made in obtaining equality 

 of properties in two directions, parallel and perpendicular to the 

 edge of a board. The greater the number of plies used for a 

 given panel thickness, the more homogeneous in properties is 

 the finished panel. Broadly speaking, w^hat is gained in one 

 direction is lost in the other. For a very large number of plies it 

 may be assumed that the tensile strength in tw^o directions is 

 the same, and that it is equal to the average of the parallel-to- 

 the-grain and perpendicular-to-the-grain values of an ordinary 

 board. 



SMOKE MAKING DEVICE 



FOR TESTING THE ClRCULATiOi 



IN DRY KILNS 



