PATTERN MAKING 



absorb moisture according to the condition of the surrounding 

 atmosphere. As there is always more or less moisture in the air, 

 and lumber of all kinds contains an amount of moisture which 

 is ever changing according to the conditions of the surrounding 

 atmosphere; this causes corresponding expansion or contraction 

 of the wood. 



Even under cover and in a dry place, wood has a tendency 

 to warp on account of the greater shrinkage of the newer as 

 compared with the older cells of the wood tissue or fiber in the side 

 of the board nearest to the outside or sap wood of the tree. The 

 inner side A of the board (Fig. 3) being closer to the heart wood, 

 is older than the side B; its cells are firmer and more compact than 

 those of B. As the board seasons, the newer and more open cells 

 of the side B will shrink faster and to a greater extent than those 

 of A, thus causing the board to draw or warp in the direction 

 indicated by the dotted lines. 



A 



Fig. 3. 



Fig. 4. 



In gluing or building up stock for a pattern, this tendency 

 may be corrected to some extent, by reversing the grain of the 

 pieces that are to be glued, and placing two outsides (as B, Fig. 3) 

 or two insides (as A, Fig. 3) together This is fully illustrated 

 in Fig. 4. 



In gluing very thin pieces together for the webs or centers of 

 pulleys and for other purposes, it is often necessary to reverse the 

 grain of the pieces, or to place the grain of one piece at rifjJit 

 angles to that of the other^ for the purpose of gaining greater 

 strength and stiffness. In such cases, ii only two thin pieces ar<> 

 used, the result, after they have been glued and dried, will be to 

 some extent as shown in Fig. 5, the shrinkage and strain of the 

 end grain crosswise of the board at , being sufficient to bond 

 the opposing thin board lengthwise of the grain at A, while on the 



