under
actual shop conditions.

The value of the file test depends upon the quality of the file and
the intelligence and experience of the person using it. The file
test is not reliable, but in the hands of an experienced operator,
gives some valuable information. Almost every steel treater knows
of numerous instances where a lathe tool which could be touched
with a file has shown wonderful results as to cutting efficiency.

Modern tool-steel practice has changed from that of the past, not
by the use of labor-saving machinery, but by the use of scientific
devices which aid and guide the skilled craftsman in producing a
steel of higher quality and greater uniformity. It is upon the
intelligence, experience, and skill of the individual that quality
of tool steel depends.

HARDENING HIGH-SPEED STEELS

We will now take up the matter of hardening high-speed steels. The
most ordinary tools used are for lathes and planers. The forging
should be done at carbon-steel heat. Rough-grind while still hot
and preheat to about carbon-steel hardening heat, then heat quickly
in high-speed furnace to white heat, and quench in oil. If a very
hard substance is to be cut, the point of tool may be quenched in
kerosene or water and when nearly black, finish cooling in oil.
Tempering must be done to suit the material to be cut. For cutting
cast iron, brass castings, or hard steel, tempering should be done
merely to take strains out of steel.

On ordinary machinery steel or nickel steel the temper can be drawn
to a dark blue or up to 900 deg.F. If the tool is of a special form
or character, the risk of melting or scaling the point cannot be
taken. In these cases the tool should be packed, but if there is
no packing equipment, a tool can be heated to as high heat as is
safe without risk to cutting edges, and cyanide or prussiate of
potash can be sprinkled over the face and then quenched in oil.

Some very adverse criticism may be heard on this point, but experience
has proved that such tools will stand up very nicely and be perfectly
free from scales or pipes. Where packing cannot be done, milling
cutters, and tools to be hardened all over, can be placed in muffled
furnace, brought to 2,220 deg. and quenched in oil. All such tools,
however, must be preheated slowly to 1,400 to 1,500 deg. then placed in
a high-speed furnace and brought up quickly. Do not soak high-speed
steel at high heats. Quench in oil.

We must bear in mind that the