106 



PATTEKN MAKING 



those in the pattern. For these reasons the holes should be cored, 

 as the core sand is firm and better able to resist the washing action 

 of the flowing metal. 



The patterns for such a face plate, a cross-section of which is 

 shown in Fig. 183, should be made as follows: The allowance for 

 finish on the face of the casting should be not less than -j^- inch, 

 and the same should be added to the diameter and also to the end 

 of the hub. Having thus determined the thickness and size of the 

 pattern, the disc should be built up of from four to sixteen sectors, 

 according to the size of the plate. If the diameter is between 24 

 and 42 inches, sixteen sectors should be cut out, each filling an arc 

 of 45, so that when eight are placed edge to edge 

 they will complete the circle. The thickness should 

 be a little more than one-half the completed thickness 

 of the pattern disc, and they should be laid up sc as 

 to form two layers, breaking joints with each other 

 as shown in Fig. 180. When the disc is formed, the 

 I hub should be first glued in position, this also being 

 built up of pieces glued together, and the whole 

 attached to a large wooden chuck and iron face-plate 

 of the pattern lathe in the same manner as described 

 for the disc-crank (Fig. 178). The rini is next built 

 upon the disc in the same way as has been described 

 for former patterns. If the face plate is very large, 

 the segments may be ^ inch or even f inch in thick- 





Fig. 183. 



ness, and to avoid end wood, eight, twelve, or even sixteen, 

 segments may be used for each layer according to the diameter of 

 the rim. 



The pattern now consists of the disc with the rim and hub in 

 position, but larger than they should be. It is, therefore, placed 

 in the lathe and carefully turned over its whole surface, each part 

 and thickness being brought to the shape and dimensions of the 

 completed pattern, care being taken to turn in a fillet of -J inch to 

 \ inch radius, depending on the size of the required easting, in the 

 angles connecting the rim and the hub witli the disc. Next put in 

 the ribs; it is not necessarv to form these out of built-up material, 

 for each may lie cut from a single piece. They should lie carefully 

 fitted to form a close joint with the rim, the disc, and the hub. 



