104 FOREST PRODUCTS 



lines of usage. By using successive layers of veneer, with the grain of 

 each board running at right angles to the grain of the board adjoining 

 it, many advantages over equal grades of lumber are claimed for it, the 

 chief among them being the following : 



(a) It is comparatively free from such common disagreeable effects 

 such as warping, checking, twisting out of shape, etc., in the presence of 

 changing temperature and atmospheric moisture. 



(b) It is stronger for general purposes. 



(c) It is relatively light in weight. 



(d) Its low comparative cost. 



(e) Its efficient use of wood, in that the core or crossbanding may be 

 made of cheaper woods or those containing minor defects. 



When making 3-ply stock, glue is applied only to both sides of the core 

 or center ply. The back of the panel or other built-up stock is first laid 

 on a truck, then the glued core is laid down and finally the top or face side, 

 the direction of the grain of the core always running at right angles to 

 that of the top and bottom pieces. The same principle is followed out 

 in making s-ply or 7-ply stock. 



The glue is applied hot and as soon as a truck load is completed it is 

 moved at once to the press. Both animal and vegetable glues are com- 

 monly used by the manufacturers of built-up stock, furniture, etc. More 

 animal glue is undoubtedly used, however, than vegetable glue. Each 

 individual operator, however, decides this for himself, and the question 

 will be an open one for some time to come. 



Many kinds of veneer presses have been developed, and at many of 

 the mills home-made or locally contrived devices have been found in 

 common use. The old hand screw press has been determined to be 

 very efficient and is still in common use in some of our most modern 

 and progressive plants. However, the hydraulic press is probably used to 

 a greater extent at this time than any other. 



As soon as a load is placed in the press a pressure of from 100 to 200 lb. 

 per square inch is exerted, depending upon the nature of the work, the 

 thickness of the built-up stock, species involved, etc. As soon as the 

 maximum load is applied, retaining clamps are placed on and the whole 

 set is removed from the press to make way for another set. The clamps 

 are customarily left on for varying periods up to ten to twenty-five hours. 

 In a large veneer plant in Wisconsin using mixed hardwoods native to the 

 state, the clamps were retained for from twenty to twenty-five hours. 

 In a large veneer mill in northern California which cuts western yellow 

 pine by the rotary process, 36 courses of 3-ply stock were left in the 



