92 



of rim, arms, and hub, and finish with three coats of shellac, sand- 

 papering smooth between each coat, as already described for other 

 patterns. 



The making of patterns for special pulleys enters largely into 

 the work of many pattern shops. In these patterns the rims arc 

 built up of segments inch to \ inch in thickness. 



To illustrate this work fully, let us take up the successive steps 

 in the construction of a countershaft pulley 20 inches in diameter 

 and of 6-inch face, made to fit a shaft If inches in diameter. 

 The pattern for such a pulley is shown in Fig. 173. The diameter 

 of the web of the arms is 5 inches, and the diameter of the hub 3| 

 inches at each end and tapering to 3f inches in diameter at the 

 arms. 



Fig. 173. 



If the rim is to be finished on the face and edges only, -jV inch 

 must be allowed for turning, making the outside diameter of the 

 pattern 20 inches, and the width of the face should be (\\ indies. 



In addition to -fa inch for finish, the draft on the outside of the 

 rim, from each edge to the center, should be in the ratio of ^ inch 

 to 12 inches, and OIL the inside of the rim the draft must be inch 

 to 12 inches. 



The thickness of the rim at its edges will be -,",. inch, and with 

 outside and inside draft added, its thickness at the arms will be 

 about ,V, inch. The inside diameter of the rim at the arms will be 

 nearly 19- 3 ^ inches. This pulley should have six straight anus 



