ng dies and punch-press dies that are difficult
to harden will seldom crack if treated in this way.

Small tools or pieces that are very troublesome because of peculiar
shape should be made of steel which has been thoroughly annealed.
It is often well to mill or turn off the outer skin of the bar,
to remove metal which has been cold-worked. Then heat slowly just
through the critical range and cool in the furnace, in order to
produce a very fine grain. Tools machined from such stock, and
hardened with the utmost care, will have the best chance to survive
without warping, growth or cracking.

SHRINKING AND ENLARGING WORK

Steel can be shrunk or enlarged by proper heating and cooling.
Pins for forced fits can be enlarged several thousandths of an
inch by rapid heating to a dull red and quenching in water. The
theory is that the metal is expanded in heating and that the sudden
cooling sets the outer portion before the core can contract. In
dipping the piece is not held under water till cold but is dipped,
held a moment and removed. Then dipped again and again until cold.

Rings and drawing dies are also shrunk in a similar way. The rings
are slowly heated to a cherry red, slipped on a rod and rolled
in a shallow pan of water which cools only the outer edge. This
holds the outside while the inner heated portion is forced inward,
reducing the hole. This operation can be repeated a number of times
with considerable success.

TEMPERING ROUND DIES

A number of circular dies of carbon tool steel for use in tool
holders of turret lathes were required. No proper tempering oven
was available, so the following method was adopted and proved quite
successful.

After the dies had been hardened dead hard in water, they were
cleaned up bright. A pair of ordinary smiths' tongs was made with
jaws of heavy material and to fit nicely all around the outside of
the die, leaving a 3/32-in. space when the jaws were closed around
the die. The dies being all ready, the tongs were heated red hot, and
the dies were picked up and held by the tongs. This tempered them
from the outside in, left the teeth the temper required and the
outside slightly softer. The dies held up the work successfully
and were better than when tempered in the same bath.

THE EFFECT OF TEMPERING ON WATER-QUENCHED GAGES

The following information has been supplied by Automatic and Electric
Furnaces, Ltd., 6, Queenstreet, London, S. W.:

Two gages of 3/4 in. diamete