PATTERN MAKING 



The allowance for draft varies with the pattern, and is often 

 greater or less on different parts of the same pattern. For example, 

 the draft on the outside of the pattern of a pulley rim 24 inches in 

 diameter and 6 inches face, should be inch to the foot, while on 

 the inside of the rim and on the hub of the pully it should be in the 

 ratio of inch to the foot. The reason for this difference is that 

 the face of the rim is often turned and finished straight, and for 

 that reason tlie least possible amount of draft that will allow of the 

 pattern being removed from the sand should be used; while on the 

 inside of the rim a greater amount of draft strengthens the 

 metal rim, which must sustain the strain and pressure of the belt. 

 In general the draft should be from ^ inch to f inch for each 12 

 inches, the latter amount in all cases where the removal of the 



J. 



Fig. 135. 



metal thus added will not greatly increase the expense of working 

 the casting. To obtain any required amount of draft correctly, a 

 draft template, kept with other tools and templates, will be found 

 convenient and useful, saving much time when changing from one 

 ratio of draft or bevel to another. It is made as follows: 



Take any straight-grained board 14 inches to 16 inches long 

 and 124 inches wide, as shown in Fig. 135. Having jointed the 

 edge a perfectly straight, draw the line 1 perpendicular to the edge 

 and 12 inches long, using a square and a sharp-pointed knife (not a 

 scratch-awl or a lead pencil). On the edge a carefully measure \ 

 inch on each side of 1>; and at the upper extremity, with the same 

 care, measure inch on each side of b; connect the last two points 

 thus found with the first two 011 the edge a, by a sharp knife line, 



