Grind the cutting edge of the chisel to the desired angle, then harden and temper it as follows: Heat about 2 inches of the cutting end to a dull cherry red and plunge about 1 inch of this perpendicularly into water; withdraw it about 1/2 inch, and keep it in motion between the first and second cooling places until the end is perfectly cold. Remove the tool and quickly polish one side with emery cloth or sandstone, watching the varying colors as they make their appearance and move toward the edge; when the dark purple or blue color entirely covers the point, thrust it into the water again and leave it there until thoroughly cooled. Regrind cautiously, protecting the temper, and test its cutting qualities on a piece of cast iron or soft steel.
=103. Hot Cutter.=—Figs. 88 and 89. Punching, fullering, forging, hardening, and tempering. Material: 4 inches of 1-1/4-inch square tool steel.
[Illustration: FIG. 88.—STEPS IN MAKING THE HOT CUTTER.]
Punch and drift an eyehole 1-3/4 inches from the end, making all sides straight and smooth, as shown at _a_, Fig. 88. With a pair of 3/4-inch fullers, form two depressions on opposite sides 1/4 inch from the eye, as at _b_, fullering the metal to 5/8 inch thick. From this place draw the end tapering to 1-1/2 × 1/8 inch, and trim it off at a right angle to the stock, as at _c_. Using a hot cutter and working equally from all sides, cut the tool from the bar 1-1/4 inches from the edge of the eye. Draw the head end tapering to about 7/8 inch from the eye, draw the corners to form a slightly octagonal section. Remove all projecting metal so as to produce a convex head. (See Fig. 89.) This will be referred to later as forming the head. Grind both sides of the cutting end equally to form an angle of 60 degrees, with the cutting edge parallel to the eye. Harden, and temper to a dark purple or blue.
=104. Cold Cutter.=—Figs. 90 and 91. Punching, forging, hardening, and tempering. Material: 4 inches of 1-1/4-inch square tool steel.
[Illustration: FIG. 90.—STEPS IN MAKING THE COLD CUTTER.]
Punch and drift an eye 2 inches from the end _a_, Fig. 90. Draw this end tapering on the sides parallel with the eye, forming convex surfaces and terminating in 1 × 3/16 inch. (See sketches _b_ and _c_.) Cut the tool off at _c_, 1-1/4 inches from the eye, and form the head.