Fig. 117.—The Yoke or Saddle.
Another view of the yoke is given at B, with one side removed. As seen here, it is used to draw weldless or solid rings after the stock has been blocked out and a sufficiently large hole has been punched in it to allow it to be hung over the pin p, which rests in the depressions previously mentioned. Hammer blows can be delivered on the exterior of the stock, thus drawing it and increasing its diameter. As this is increased, larger pins should be used, to produce a smoother and more evenly drawn ring.
The yoke, shown at C, is being used as a bridge for drawing the ends of a solid forged jaw. By using it for purposes like this, considerable hand labor may be saved.
Fig. 118.—A, Bolster; B, a Plug Punch in Position for Use.
130. Bolsters or collars (a, [Fig. 118]) are used for punching holes, upsetting metal for bolt heads, and similar operations. They should be made of soft steel.
131. Punches.—At b, [Fig. 118], a plug punch is shown in position on the metal over a washer or bolster ready for punching. When properly located, a few blows of the hammer will force the punch through the metal and produce a smoothly finished hole.
Notice that the punch is made somewhat tapering, and that the heavier portion is driven through first. Precaution should be taken not to have the punch fit the bolster too closely or be too long, also to have it directly over the hole in the bolster before attempting to drive it through.
Holes can be punched with ordinary handle punches, but care should be taken not to have them too long; even then a bolster or something must be used, so that the punch can be driven clear through the metal and not come in contact with the lower hammer die.
132. Steam Hammer Work.—The following exercises are known as machine forgings. They will require the use of the steam or power hammer and the tools just described. It will be necessary to know beforehand what parts of the work are to be finished, so as to provide a proper allowance at those places. The term “finished” means that the surface is to be removed by the machinist, and the work made smooth and to the required dimensions.