PATTERN MAKING 



111 



in position; the tendency being to sag in the middle, or float on 

 the molten iron, and thus make the upper side of the casting too 

 thin, all of which is avoided in the double pattern. 



Fig. 194. 



A pattern for the return bend, Fig. 196, can be built up and 

 constructed in the same manner as described for the elbow; the 

 semicircular returns, not only for the pattern, but also for the core 

 box, being turned in the lathe, together with 

 the ends and core prints for the pattern. 

 As there will be no middle support for the 

 core in this case, the core prints must be 

 made, as shown in the half pattern, Fig. 197, 

 of sufficient length to balance the heavy semi- Fig. 195. 



circular core, and also to keep it in its true position in the mould. 



The small wood lathe chuck, a vertical section of which is 

 shown in Fig. 198, will serve as a simple illustration of the long 



Fig. 196. 



core print and balanced core. The casting must be counter cored ; 

 that is, the cored opening must be enlarged at the forward end, 

 adding to the size and weight of that end of the core, which, as 



