ull white heat, 2,200 to
2,250 deg.F., that is, until the tool starts to sweat at the cutting
face. Cool the point of the tool in a dry air blast or preferably
in oil, further cool in oil keeping the tool moving until the tool
has become black hot.

To remove hardening strains reheat the tool to from 500 to 1,100 deg.F.
Cool in oil or atmosphere. This second heat treatment adds to the
toughness of the tool and therefore to its life.

GRINDING TOOLS.--Grind tools to remove all scale. Use a quick-cutting,
dry, abrasive wheel. If using a wet wheel, be sure to use plenty
of water. Do not under any circumstances force the tool against
the wheel so as to draw the color, as this is likely to set up
checks on the surface of the tool to its detriment.

FOR MILLING CUTTERS AND FORMED TOOLS

FORGING.--Forge as before.--ANNEALING.--Place the steel in a pipe,
box or muffle. Arrange the steel so as to allow at least 1 in.
of packing, consisting of dry powder ashes, powdered charcoal,
mica, etc., between the pieces and the walls of the box or pipe.
If using a pipe close the ends. Heat slowly and uniformly to a
cherry red, 1,375 to 1,450 deg.F. according to size. Hold the steel at
this temperature until the heat has thoroughly saturated through
the metal, then allow the muffle box and tools to cool very slowly
in a dying furnace or remove the muffle with its charge and bury
in hot ashes or lime. The slower the cooling the softer the steel.

The heating requires from 2 to 10 hr. depending upon the size of
the piece.

HARDENING AND TEMPERING.--It is preferable to use two furnaces
when hardening milling cutters and special shape tools. One furnace
should be maintained at a uniform temperature from 1,375 to 1,450 deg.F.
while the other should be maintained at about 2,250 deg.F. Keep the
tool to be hardened in the low temperature furnace until the tool
has attained the full heat of this furnace. A short time should be
allowed so as to be assured that the center of the tool is as hot
as the outside. Then quickly remove the tool from this preheating
furnace to the full heat furnace. Keep the tool in this furnace only
as long as is necessary for the tool to attain the full temperature
of this furnace. Then quickly remove and quench in oil or in a
dry air blast. Remove before the tool is entirely cold and draw
the temper in an oil bath by raising the temperature of the oil
to from 500 to 750 deg.F. and allow this tool to remain, at this