These dies are used in forming a loop such as is shown in Fig. 366 and marked "After Curling". The loops on hinges and similar pieces are examples of its work. The stock is first punched out as shown at the upper left-hand corner, and the blanks are forced into a curling die of the design shown at C. The punch D has a V-shaped impression in its face, as shown.
In making this die, the block C is machined to size. The hole E is drilled, reamed, and lapped to size; the lapping also produces a smooth hole, if a round, revolving lap of the right size is used. The slot F is then milled.
If the stock is comparatively soft or is easily bent, and if the die is to be used for but a few holes, it need not be hardened; if intended as permanent equipment, it must be hardened, preferably by the pack-hardening process.
Fig. 366. Curling Die and Work. Before and after Operation.
Fig. 367. Another Form of Curling Die.
Another form of curling die, Fig. 367, is used in curling a loop around the end of a circular shell or vessel. The stock entering the circular-shaped portion of the punch is made to conform to the size of the circle.
Fig. 368. Wiring Die.