Fig. 102.—The Hack or Cutter.
117. The hack or cutter ([Fig. 102]) is used for nearly the same purposes as the hot cutter already described. It should be made of tool steel from 0.80 to 0.90 per cent carbon. The head or top is made convex, as shown, and not more than 5⁄8 inch thick, tapering equally on both sides to the cutting edge, which may be made either 3⁄16 or 1⁄4 inch thick. It should be ground straight and parallel to the top and tempered to a dark blue.
The blade is about 21⁄4 or 21⁄2 inches wide, unless intended for heavy forgings, when all dimensions should be increased. The width of the blade should not be too great, however, for the broader the cutter, the greater its liability to glance sidewise or turn over when the blows are delivered upon it. The length of this cutter may be from 33⁄4 to 4 inches.
The handle may be about 28 inches long, approximately 3⁄4 inch in diameter at a and gradually tapered towards the end, where it is about 1⁄2 inch. The portion indicated at b is flattened to an oblong section, as shown, to allow springing when the blows are delivered and to prevent bruising the hands.
118. The circular cutter ([Fig. 103]) is made of the same material and with a handle of similar dimensions and form as the hack. A section of the cutting portion on a-a is shown, and suitable dimensions given. If convex ends are to be cut, the perpendicular side of the blade should always be on the inner side of the curve, but on the outer side for concave ends.
Fig. 103.—The Circular Cutter.
An assortment of these cutters with various-sized arcs may be provided to suit requirements, but quite frequently the curved cutting portion is altered to suit the particular work at hand.
Fig. 104.—The Trimming Chisel.