the wire, and whose width equals line AM of Fig. 213, plus ⅜ in. for clearance. Rivet holes for the hinge straps should be laid out carefully. A double edge is provided on three sides to be formed according to the sectional view, A ½-inch hem will serve to stiffen the cover at the hinged edge.
Pattern of Rotating Screen (Fig. 222).—The rotating screen is made of 3 mesh No. 18 wire galvanized netting. It is in the form of a frustum of a cone as shown by Fig. 222. A cast-iron frame, shown to the left of Fig. 222, is provided for each end of the screen. The outer face of this frame is tinned and the netting is soldered to it. The edges of the screen have a ⅜-inch lock turned outward, and a galvanized-iron clinch strap is slipped on, hammered down, and the whole seam "tacked" with solder. The pattern of the frustum, Fig. 223, is obtained in the manner described in Chapter V.
Pattern of Rear End (Fig. 225).—A rear elevation of the sifter is drawn as shown in Fig. 224, all dimensions being taken from Figs. 213 and 214. A line of stretchout is drawn and upon it are set off the spaces AC and CD of Fig, 213. Measuring lines can now be drawn and extension lines dropped from points A, C, and D of Fig. 224, Straight lines connecting points of intersection will give the outline of the pattern, A ⅜-inch wire edge should be added to the top, and ⅜-inch double edges to the other three sides.
Pattern for Galvanized Screen (Fig. 229).—Figure 226 shows that part of the sectional view. Fig. 213, that has to do with the screen and shield, while Fig. 227 is a front elevation. The pattern for the galvanized iron shield is copied directly from Fig. 227, and the necessary laps added as shown by Fig. 228. The line PR is extended to the right of Fig. 227, making RW equal in length to BS of Fig. 226. With R as a center, arcs are drawn from points 15, 5, 6, 7, 8, and N, cutting the line RT, which is drawn at right angles to RW. At any convenient point, a line PR, Fig. 229, is drawn equal in length to line PR of Fig. 227. With R and P of Fig. 229 as centers, and a radius equal to WN of Fig. 227, arcs interesting at point N are drawn in. With P and R, Fig. 229, as centers and radii equal to W–8, W–7, W–6, W–5, and W–15 arcs bearing away from point W are drawn. Starting at point N of Fig. 229, the distances N–8, 8–7, 7–6, etc., should be made equal to distances N–8, 8–7, 7–6, etc., of the profile of the circle in Fig. 227.
