Punches need not be tempered, because the strength of the steel from which they should be made will withstand the force of the blows, and also because the metal is generally hot when the punches are used; therefore the temper would be quickly drawn out of them. If sheet metal or light material is to be punched cold, it is advisable to harden the punch slightly; then the hole may be punched through from one side, while the metal is held on something containing a hole slightly larger than the punch. This method has the effect of producing a smoothly cut hole, provided the metal is properly placed.
[Illustration: FIG. 12.—THE TOP AND BOTTOM SWAGES.]
=25. The top and bottom swages= (Fig. 12) are made with semicircular grooves of different sizes to fit the various diameters of round material. The former has an eye for the insertion of a handle by which it is held when in use. The eye should be crosswise to the groove in the face. The bottom swage is made with a square projecting shank to fit loosely into the hardy hole of the anvil. It should be placed in position for use with the groove crosswise to the length of the anvil, unless the form of the forging should require otherwise. Swages are conveniently used for smoothing round material after it has been welded, or for swaging parts of a forging after they have been roughly hammered out. By dipping the top swage in water occasionally while in use, the work can be made much smoother and the scale of oxide removed; this is called water swaging.
[Illustration: FIG. 13.—THE TOP AND BOTTOM FULLERS.]
=26. The top and bottom fullers= (Fig. 13) are made in pairs with convex semicircular projections or working faces, whose diameters should correspond, if intended to be used together. As the former is quite frequently used alone, it may be made of any desired size. The top fuller, like the top swage, is made to be used with a handle; the bottom fuller, fitted to the anvil like a bottom swage, generally is placed for use with the length of its face parallel to the length of the anvil.
They are used together for forming depressions or shoulders on opposite sides of the material; from the shoulders thus formed, the metal may be forged without disturbing them. They are used also for rapidly drawing out metal between shoulders or projections which may have been previously made and are to be left undisturbed. The top fuller is used singly in making scarfs for welding, in forming grooves, in smoothing fillets and semicircular depressions, or in forming shoulders on only one side of metal.