A great amount of trouble is experienced in some shops when attempting to use small piercing punches to produce holes in stock as thick as the diameter of the punch, or thicker. This difficulty can be obviated by using guide bushings in the stripper plate to support the punches and guide them to the opening in the die. The bushings should be made from tool steel, hardened, the holes ground and lapped to an exact fit for the punches; or, in the case of very small punches, where grinding is out of the question, the hole may be lapped to size, and the outside ground to size to force it into the hole in the stripper plate.
Fig. 348. Die with Guide Bushings.
The guide bushings must be in exact alignment with the openings in the die. Fig. 346 shows a form of die provided with guide bushings bb, for the punches aa. The dies cc are made from tool steel, hardened, and forced into a machine-steel die block. The punches are made from drill rod and are held in place by binding screws dd and adjusting butt screws ee. Between the binding screws d and the punch, at the end that bears against the punch, is a piece of wire of semicircular shape. This allows the punch to be set down as the punching end is ground away.
In the case of gang punches and dies, used in the production of perforated sheet-metal work, which have sometimes several hundred piercing punches working into one die, it is customary to provide each punch with a guide bushing.