PATTERN MAKING 91 



the rim, must be tangent to the edge of the arm and to the circle 

 (8f inches diameter) which marks iV inch less than the inside 

 diameter of the rim as shown at c c. 



Having laid out" the arms as above, and as shown in the draw- 

 ing by the dotted lines, saw them to shape and round them up to 

 an elliptical form as shown in the cross-section at e, Fig. 169. The 

 finished shape of the arm at any point in its length, is found by 

 drawing a cross-section of the arm at that point, as in Fig. 170. 



Divide the cross-section equally by the line A B ; measure -jV 

 inch ; as at a c df; and with dividers adjusted so as to be tangent to 

 the sides of the cross-section of the arm, and to pass through a c 

 and df, draw the curves a 5 c and d ef. 



After filing and working off the sides of the arms to these 

 curves, the angles at a c d and f are carefully rounded with sand 

 paper, care being taken not to lessen the width of the arm at any 

 point. The result will be as shown in Fig. 171, which gives a 

 strong, firm edge to the arm, and one which will not break or splin- 

 ter off while being rammed up in the sand. 



The arms thus shaped and finished are cut or let \ inch into each 

 half of the rim, and great care must be taken to keep them central with 

 the rim. Before marking the rim for the mortises which will 

 receive the ends of the arms, test their 

 positions with the dividers, spacing from 

 the center of the arms to the outside edge 

 of the rim, and moving the arms until a 

 central position is obtained; after which, 

 with the point of a knife or awl, scribe 

 around the end of each arm. and proceed to 

 cut, with a chisel, the mortises \ inch deep Fig. 172. 



into each of the half rims, and so cut and fit that the two pieces of 

 the rim may meet and form a close joint, after which they are glued 

 and clamped together over the arms with hand screws. 



The hubs are next turned, each from a solid block, or better 

 from thin pieces \ inch to inch in thickness, each thin piece being 

 placed crosswise on the other, as shown in Fig. 172. The hubs 

 must be turned with a draft or taper of inch to 12 inches, and 

 have a curve of ^-inch radius at the base where they unite with 

 the arms. After gluing on the hubs, smooth off all connected parts 



