PATTEKN MAKING 



73 



As the work progresses, the accuracy of the curve is tested by 

 means of a try square, or other 90 angle, as shown in Fig. 146a. 



The tapered end of the box c (Fig. 143) is turned from a block 

 of wood, screwed to the face 

 plate of the lathe as shown in 

 Fig. 147. After the hole is 

 turned to the required depth, 

 f inch, and to the required size, 

 lg inches on the outside, and 

 If inches at the bottom, it is 

 removed frjm the face plate 

 and the piece c is cut out, as Fig. 147. 



shown by the dotted lines in Fig. 147. This piece c is glued and 

 nailed to the end of a. The two ends of the box are now given a 

 slight draft, ( inch in 12 inches) to allow the half core to leave the 

 box easily. The end strips d and d (Fig. 143) are then nailed on 

 and the box is complete. 



I 



FINISHING PATTERNS. 



Having completed the pattern and its core box, the surface of 

 the wood must be covered with some material which will render it 

 hard, smooth, and impervious to the moisture in the sand, and at 

 the same time make it easier to be withdrawn from the mould. 

 Pure grain-alcohol shellac-varnish is the best for this purpose. All 

 cheap substitutes, such as wood-alcohol shellac, or copal varnishes 

 should be avoided. They become flaky and scale off, and do not 

 stand the exposure and moisture. Pattern makers generally make 

 their own shellac varnish, buying only the best quality of shellac 

 gum, and using 95 per cent proof alcohol. The proportions are 

 three pounds of gum to one gallon of alcohol. The gum is put in 

 a wide-mouthed bottle, or earthen jar, and the alcohol poured over 

 it, and if well stirred three or four times during the day will (if the 

 alcohol is of the best,) give a smooth, clear, orange-colored varnish 

 ready for use. 



A good grade of "white grain-alcohol shellac" may be made 

 from bleached gum, or can be bought from the dealers, but it dries 

 more slowly and does not produce so hard a surface as the orange 

 shellac. 



