The heavy engine-crank pattern illustrated by Fig. 192 should be built of five layers of stock, gluing heart sides and bark sides of each piece together, as shown in Fig. 193. Dress the stock true on one side and edge for a working face and a working edge. Machines-plane the opposite side and edge parallel to these faces. Lay out the plan of the crank on one face and also a side elevation on one side of the stock. Square around the stock for the location of the holes - 15-inch centers - and bore 1-inch holes on both sides of the stock at these centers. Carefully band saw to line a, Fig. 193, and leave stock at b so as to keep the top of the stock parallel to the band-saw table when sawing the line c. This stock b may be removed with a chisel after all band-saw work is completed. Have the band-saw table tilted when sawing to line c so as to produce a slight draft - 1/8 inch in 12 inches - to the sides of the pattern.

Flat Back Patterns Solid Engine Crank Construction 500140Detail Drawings for Heavy Engine Crank.

Fig. 192. Detail Drawings for Heavy Engine Crank.

Turn a nowel and cope core print 3$ inches and also 2f inches in diameter, according to the standard adopted for core prints. The bosses e and f are to be made of flat stock 3/8 inch thick. Prepare a wood faceplate with a 1-inch pin at its center. Having a 1-inch hole at the center of the boss, fasten the bosses to the faceplate with four 3/4-inch wire nails; now turn them to the diameters required by the drawing and bevel the edge about 30 degrees. Nail and glue on the bosses, being sure the holes are in line with the holes in the body of the pattern.

Diagram of Pattern for Crank, Fig. 192.

Fig. 193. Diagram of Pattern for Crank, Fig. 192.

The sectional view in Fig. 192 shows the form of the crank at mid-length, and the pattern should be finished to this form, using a template to test the accuracy of the round corners. The dowels of the nowel core print should fit tightly, but are not to be glued to the pattern unless it is known that the size of the cored hole will not be altered. The cope core prints should fit loosely, so that they can be removed while ramming the nowel mold. The mold parting will then occur on line pp, Fig. 193, and the parting will be coped down to the round corners. Patterns like Fig. 193 and Fig. 195 are known as flat backed; no part of the pattern except the cope core prints extends into the cope mold.