56 



PATTERN MAKING 



In the case of moulding ;> hollow object, the internal cavity in 

 the casting is formed by means of a dry sand core, which rests in 

 impressions made in the sand by core prints attached to, and 



forming a part of, the pattern. 

 To illustrate this, let it be required 

 to cast the hollow cylinder shown 

 in Fig. 106. The wooden pattern 

 Fig. 105. necessary to produce this hollow 



cylinder is shown in Fig. 107, which, as will be seen, represents 

 the cylinder only externally by the part A. 



The core prints, one on each end .of A, are represented by x 

 and y. These projections form part of the pattern, and make their 

 impressions in the sand with the part A, which alone represents 



Pig. 106. 



Fig. 107. 



box will be the extreme length of the pattern including so and y, 

 and tho inside width will be the exact diameter of the core prints. 

 In this case, the core being a cylinder, only a half core box (Fig. 

 108) is used. In it are made two semi-cylindrical cores, which, 

 after being dried, are cemented together, thus forming the com- 

 plete cylindrical core required. 



To mould this halved or parted pattern as it is called, the 

 upper half of the pattern is laid on the 

 moulding board, and the drag is turned 

 over it with the bottom side of the drag 

 up and the parting side on the mould- 

 ing board, as shown in Fig. 109. After 

 b< -ing "rammed up," the drag and mould- Fig. 108. 



ing board are turned over and the board removed, when the part- 

 ing of the pattern will be exposed, tin- hall' pattern boing imbedded 

 in the sand. 



