PATTERN MAKING 103 



diameter of the pattern 16-i%- inches, and the thickness of the disc 

 -f$ inch. A sectional view of the pattern is shown in Fig. 179. 

 The disc for this pattern must be made of two thicknesses of 

 sectors, six in number for each thickness, which, after being fitted, 

 glue-sized, and glued together, are planed off true on both sides, 

 and glued on each other so as to break joints, as shown in Fig. 180. 

 When dry, the disc thus obtained is sawed to a diameter of 16| 

 inches and glued to the wooden chuck on the iron face-plate of the 

 lathe with small sectors of thick paper between, or else glued to 

 small blocks on the chuck, from which, after turning, it can be cut 

 as illustrated in Fig. 168. The rim is now built up on the disc out 

 of segments f inch or ^ inch in thickness, as directed for the 20- 

 inch pulley (Fig. 173), with not less than six segments to each 

 course. The hub is glued up as described, and, after gluing 

 on the disc, the whole is turned to the required size and shape. 



Fig. 179. 



Fig. 180. 



In the case of this disc-crank pattern, a small disc of paper 

 (or a block, if blocks are used) should be placed, without gluing, 

 under the center of the disc, to prevent looseness and vibration 

 while being turned in the lathe. The boss #, to receive the wrist 

 pin, must be glued up in the same way as the hub (see Fig. 172), 

 and turned on the lathe, after which it is fitted into position as 

 indicated in Figs. 178 and 179. The counter- weight b is next shaped 

 from a single piece, or it may be glued up of several thicknesses of 

 |-inch stock. In sawing this block to shape, the band-saw table 

 should be tilted so as to give it a draft of f inch to 12 inches. Give 

 the inside of the rim, the hub, and the boss a, the same draft, but 

 the outside of the rim should not have a draft of more than & inch 

 to 12 inches. 



