A sub-press is a small self-contained press which is operated by a large press. It is extensively used in watch and clock shops for punching the movements. Fig. 379 shows samples of work done on this press. Figs. 380 and 381 show different styles of sub-presses.
While sub-presses differ in design, the pattern illustrated in Fig. 382 is well adapted for general use. The upper portion A of the press, as shown in cross-section, is bored out tapering to receive the Babbitt sleeve, and the feet are bored to fit on the base. A thread is cut at the top to receive the nut used in holding the Babbitt lining tightly in place. The die goes in the base, and is made in the usual manner. The punch, which is held in the plunger B, is carefully set, and the space around the plunger is filled with Babbitt metal, poured in the usual manner. In order that the plunger shall be held from turning, three or four parallel grooves are milled as shown, before the Babbitt metal is poured, the latter, filling the grooves, acts as a guide.
The slot at the top of the plunger engages loosely in the gate of the press, so that absolute accuracy in the working of the ram of the press is not essential. A good press, however, is always to be preferred. It is considered good practice to adjust the press so that the punch does not actually enter the die, but comes just far enough to punch the blank out of the stock without the edges of the die and punch coming in contact.
Fig. 379. Work Performed by Sub-Press.
Fig. 380. Two Forms of Sub-Press.
The sub-press is especially valuable for complicated dies, and many compound dies are used in this form. Complicated dies, which, when made in the ordinary way, would produce but a comparatively few pieces, will, when sub-pressed, punch from 20,000 to 50,000 pieces.