PATTERN MAKING 



117 



built and fitted centrally on the upper half of the cylinder pattern 

 as in Fig. 213. The projections a, a, which give the extra width 

 of metal for the bolts of the chest cover are left loose, being kept 

 in place by long wires or dowel pins as shown at c, c, so that they 



Q R 



Fig. 214. 



can be withdrawn separately from the mould after the main part of 

 the pattern has been taken from the sand. These four strips should 

 be recessed into the corners of the chest one quarter inch, as shown 

 by the dotted lines, to prevent them from being rammed out of 

 place after the dowel pins are taken 

 out. The boss i for the valve-rod stuff- 

 ing box, and also the boss k around 

 the steam-pipe opening, must be loose 

 so as to be taken out of the mould 



5 T 



after the pattern has been removed. Fig. 215. 



The pieces o, o, at each end of the steam chest, which form a 

 thickness of metal over the steam ports, are next fitted in place, as 

 also the exhaust passage n which must be parted on the line of 

 parting of the two halves of the cylinder pattern. 



The main core box 

 for the cylinder is 

 made in the same way 

 as has been already 



described for Fig. 208. 

 The steam-chest core 



G H F 



Fig. 216. 



box is shown in. Fig. 214, in which P is a side view, one side of the 

 box being removed to show the valve seat v, and the core prints x, 

 z, and 2/, which form recesses in the core, into which the upper ends 

 of the two steam inlet cores, and the central exhaust passage core 

 are placed. Q is an end view of the box with one end removed, 

 and R is a view looking into the box from above. 



For the core forming the exhaust passage, two half core boxes, 



