Section 13. qxd

front rake
angle of 5 to 15
to give a
curl to the chip, provide a cleaner cut surface, and reduce the power
consumption. The 
land
back of the cutting edge, which may be 
to 
in (0.4 to 1.6 mm) wide, usually is provided with a land relief varying
from 1 to 3
with a clearance of 30 to 45
.
The heavier the feed per tooth or the longer the surface being broached,
the greater must be the 
chip clearance
or space between successive teeth
for the chips to accumulate. The root should be a smooth curve.
Broaches are generally made of M2 or M7 high-speed steel; carbide
is also used for the teeth of large broaches. Broaches of complicated
shape are likely to warp during the heat-treating process. For this rea-
son, in hardening, they are often heated in a vertical cylindrical furnace
and quenched by being hung in an air blast furnished from small holes
along the side of pipes placed vertically about the broach.
Push broaches
are usually shorter than pull broaches, being 6 to 14 in
(150 to 350 mm) long, depending on their diameter and the amount of
metal to be removed. In many cases, for accuracy, four to six broaches
of the push type constitute a set used in sequence to finish the surface
being broached. Push broaches usually have a large cross-sectional area
so as to be sufficiently rigid. With 
pull broaches,
pulling tends to
straighten the hole, whereas pushing permits the broaches to follow any
irregularity of the leader hole. Pull broaches are attached to the
crosshead of the broaching machine by means of a key slot and key, by
a threaded connection, or by a head that fits into an automatic broach
1
⁄
16
1
⁄
64
1
⁄
2
1
⁄
4
1
⁄
8
2
l