444 APPLIED SCIENCE 



by coating the chaplet with a clay wash or by leaving it 

 tinned. 



513. The Drawing of Patterns and Castings. Since 

 patterns are entirely enclosed in sand, provisions must be 

 made for drawing them out. This process involves drafting 

 or tapering. Draw or draft is the amount of taper or bevel 

 given to the sides of projections and edges of patterns em- 

 bedded in the sand, so that when the pattern is drawn, after 

 the process of molding, the sand will not be broken above 

 the edges. Should the edges be broken it would be necessary 

 for the molder to "patch" the mold. Patching is unde- 

 sirable, not only because of the time consumed, but because 

 of the liability of leaving a weak place in the mold. The 

 draw may be from y$ in. to 1 in. per foot of length and is 

 usually indicated as J/ in., J4 m -> % -, 1 i n -> etc., draw, 

 the fact that this draw refers to one foot of length being 

 understood. 



As much draw as possible, considering the machining of 

 the casting, should be used, for the greater the draw, the more 

 readily the pattern can be molded. Since a molder may 

 make many impressions or molds each day from a single 

 pattern, the amount of draw should be carefully considered 

 in designing it. 



While the draw on the pattern may, and does, vary, that 

 on the core-prints is constant. Although no universal draw 

 has been formulated, it is the custom in each shop to have 

 a constant draw, so that the cores made and pointed in 

 core machines may always fit the impression of the core-print. 



A safe rule for tapering core-prints is to give the drag- 

 print a draw of }/% in. for each inch of length, and the core 

 print Y% m - draw for each inch of length. 



