102 



PATTERN MAKING 



holes bored in the pattern, or they may be turned flat on both ends 

 and nailed on. Core prints x and x must have no more draft than 

 is given to the body of the pattern (\ inch to 12 inches); but z and 

 z, which will be moulded in the cope, must be \ inch less in diame- 

 ter at the upper end than the diameter at the base. 



The heavy engine-crank pattern illustrated by Fig. 177, differs 

 but little in general construction from that shown in Fig. 176, ex- 

 cept that, being large and heavy, 

 it must be built up out of thin 

 stock, as shown in the drawing. 

 The stock is first glued up to 

 the necessary thickness, after 

 w r hich it is laid out and sawed to 

 shape as one piece, the saw table 

 being tilted slightly to give the 

 Fig. 177. required draft, which in this case 



must not be more than ^ inch or -^ inch to 12 inches. 



The bosses e and f are also glued up out of thin stock, the 

 pieces being crossed so that the grain of each will be at right 

 angles to that of the other, as illustrated in Fig. 172, after which 

 they are turned with a draft of ^ inch to 12 inches, and fitted to a, 



Of the four core prints 

 only x and x will have exces- 

 sive draft, as explained in con- 

 nection with Fig. 176; z and 

 z must have no more draft 

 than the body of the pattern. 

 The parting of the mould, as 

 in the former case, will be on 

 the line F G. 



In Fig. 178, is illustrated 



a finished cast-iron disc crank 





for an engine of 12-inch stroke. This crank is finished on the face, 

 on the outer edge, and on the end of the hub. It is bored out 3 

 inches to fit on the engine shaft, and 2^ inches to receive the wrist 

 pin. An addition of J inch must be allowed on the pattern for 

 finish of the face, and the same on the end of the hub; , : ',, inch 

 will be sufficient to add for finish on the outer rim. innking the 



