440 APPLIED SCIENCE 



smooth surface. The surface is sandpapered again, after 

 which shellac varnish is applied to give a hard, smooth finish 

 and to fill the pores. This last process helps the pattern to 

 withstand the action of the damp sand and the hard usage 

 to which it is subjected in the foundry. 



Core boxes, corresponding to the interior of the finished 

 casting are next made. These boxes must be so constructed 

 as to facilitate the work of the core-maker. They must 

 possess a high degree of durability and they must be accurate, 

 or the casting when finished will not have the proper thick- 

 ness of metal. 



Patterns are usually made from seasoned white pine. 

 When many castings are to be made in the same mold, 

 however, mahogany or cherry are preferable. Mahogany, 

 having a hard, dense surface, is invaluable for small, fragile 

 patterns or for patterns which are in constant use. Though 

 more difficult to work than pine, it will stand much more 

 abuse. Cherry, another durable wood, is cheaper than 

 mahogany and preferable for some kinds of work. 



508. Flasks and Cores. The box in which the sand is 

 molded from the pattern is called a flask. It consists of 

 two or more parts, open at top and bottom. Its purpose is 

 to hold in position the sand of the mold during the operation 

 of molding. The lower or bottom part of the flask is called 

 the drag and the top or upper part the cope (Fig. 206), while 

 any intermediate parts are termed cheeks. The parts of 

 the pattern are also known as the drag, cheek, or cope accord- 

 ing to the portion of the flask in which they were molded. 

 If a special pattern is to be constantly used in manufacturing 

 a certain line, it is well to make both the flask and the pattern 

 of metal for the sake of wear and durability. 



