All machine drawings should designate the parts that require finishing, by either the entire word or just the letter “F.” The symbol is more convenient to use for only certain parts, but if the entire forging is to be finished, it may be indicated by “finished all over.”
133. Crank Shaft.—[Fig. 119]. This is shown without dimensions or finish marks. Select stock sufficiently heavy to produce a forging equal to that shown at b.
Make two depressions with the checking tool, as shown, the distance c between them corresponding with the dimension a on the crank. Draw the ends square and straight on the lower side, as shown at d, then octagonal, and then round. In this way the fillets and shoulders will be equal, as shown at e. The two ends should be swaged smooth and round, then made perfectly straight and at right angles to the crank.
Fig. 119.—Steps in Making a Crank Shaft.
134. Connecting Rod.—[Fig. 120]. The volume of the material required for section e must first be estimated. Then ascertain how many inches of the selected material will be required to give this volume. This will be the distance b for the fullering shown at a. The sizes of the fullers to be used should be the same as the required radii r. Fuller in the depressions as shown, so that they will correspond with the dimensions g, h, and l of the finished rod. The metal between g and h should then be drawn slightly tapered, as shown in the top view, and to a uniform thickness l. The small end must now be drawn to the proper size and trimmed with the circular cutter. Make the rod perfectly straight, with the ends parallel to each other and to the rod.
Fig. 120.—Steps in Making a Connecting Rod.
135. Rod Strap.—[Fig. 121]. This forging is begun by blocking out, as shown at B, with e a little greater than h and plenty of stock at f. The length k must equal l, with a slight allowance of surplus metal for the bending operation.
Sketch C shows the method of bending. A forming block m should be provided for this, the width of which corresponds nearly with the dimension g, and the thickness is somewhat greater than that at d. The length may be equal to the inside length of the finished strap, but it could be used if shorter. By placing this block perpendicularly on the bottom die, with the forging resting on it and a small piece of metal n for a blocking on top of that, the upper die may be brought down and a full head of steam turned on while the stroke lever is held down. Both ends can be bent down simultaneously with sledges.