PATTP^KN MAKING 97 



This method will bo found convenient for all pulleys of mod- 

 erate width of face ; but as the spaces between the arms cannot be 

 turned out, great inconveniences in reaching these places will be 

 found when the face of the pulley is twelve or more inches in 

 width. These spaces must be dressed out by hand. 



The instructions regarding the construction of the last three 

 patterns should be studied carefully, because the general points 

 involved enter largely into the construction of patterns of all kinds, 

 and especially for all work having arms with circular rims. 



When pulleys of standard sizes for line shafting are manu- 

 factured in quantities, a skeleton pattern consisting of hub, arms, 

 and an independent iron rim is used. This iron rim is of moderate 

 width but may be used for obtaining any width of face desired. 



Wooden patterns complete in themselves, as that described for 

 Fig. 173, are used for all special pulleys 011 machines when the 

 required sizes and widths, as also hubs and connections, are irregu- 

 lar and designed only for the special machine, so that the making 

 of pulley patterns is important in nearly all foundries and pattern 

 shops. 



Where the iron rim is to be made, the same care is necessary 

 in the building up of the original wooden pattern. It must be 

 remembered that before the final casting is obtained, two shrink- 

 ages will take place; first, the shrinkage of the original casting 

 from which the iron ring is turned, and then the shrinkage of the 

 casting made from this pattern. In addition to this, there must be 

 the allowance for turning the ring both inside and out and for the 

 turning of the outside pulley rim. Suppose the pattern is to be 

 made for a pulley two feet in diameter. The usual allowance for a 

 single shrinkage is made by the shrinkage rule. In this case the 

 allowance must be doubled. Thus in the above pulley, the diame- 

 ter of the wooden pattern becomes 24J + ^ = 24^ inches, standard 

 rule measurements, or 24 -f- \ = 24^ inches, shrinkage-rule meas- 

 urements. As a very smooth surface, free from holes, is required, 

 \ inch in diameter, or inch all around, must be allowed for out- 

 side finish on the iron ring, and ^ inch for finish on the rim of the 

 cast-iron pulley. 



The outside diameter of the original wooden pattern is 24^ + 

 = 24| inches, with shrinkage rule. If the final thickness of 



