The mirror., 1922-04-27

first, because of the practical impossibility
of cutting die of this form with absolute
precision at reasonable cost, and second,
because the curve profile of the standard
spur tooth could not be accurately re-
dressed when worn. The rack form of
tooth in the involute system of gearing,
however, avoided these drawbacks and
was adapted as the standard for die rolls
for the production of all spur type gears.
The master form of die tooth is applica-
BILE to the formation of helical or spiral
spur gears by making the tooth spaces of
the die in the form of oblique straight cuts
across its face, although the resulting
tooth spaces are somewhat deeper at the
center than at the ends. On the gears
nodded from die rolls of this form the
teeth are, of course, somewhat shorter and
heavier at the ends than in the center
The gearing so formed is actually stronger
than gears of the same pitch with teeth of
uniform dimensions, as the greater CEN
trail tooth depth tends to increase the arc
of contact at the center of the face.
Herringbone gears may be as accurately
and cheaply produced as the other types
by the simple expedient of a compound die
roll, made up, to enable easy redressing,
of two helical die rolls of opposite spiral
angle, keyed and securely bound together
when functioning, and readily taken apart
for separate dressing of the two halves.
Not only can perfect herringbone spur
gears be formed by this method, but ap
plication of the same principle to bevel
gears by forming compound dies of two
helical bevel gear dies, will produce, as
rapidly and as cheaply, a perfect herring
bone beve gear. This form of gear has
never before been possible of practical pro-
duction.
In the actual process of rolling the gears
the blanks heated to a temperature of be-
tween 1000 and 2,1OO deg, F., are mounted
On the work arbor of the machine and
securely clamped in place by means of
powerful automatic chuck, mechanical,
pneumatic or hydraulic. The arbor carry
ing the blank and that carrying the die
roll, having been adjusted to the proper
angle in respect to each other as required
by the type and dimensions of the gears to
be rolled, the blank and die are then
rolled in precisely synchronized contact
under a rolling pressure of from 10 to 20
tons.
The die roll is automatically advanced
to positive contact with the blank as the
rolling commences. As the rolling con-
tinues at high speed the die roll is ad-
vanced until the teeth of the die have
penetrated to nearly full depth in the
plastic blank. The advance is then
slowed somewhat until the formation of
the gear is completed and die and gear
are in full engagement. This movement
of the die roll is automatically produced
by means of smooth positive cam mechan-
ism which accomplishes a regular and
constant progression in the first stage and
gradual retardation as the die approaches
full depth. This cam mechanism is also
designed to assure full penetration of the
die teeth before the heated blank has cooled
below its critical temperature and then
continue the rolling with no die advance
ment until the blank has cooled somewhat
below this point.
As the rolling is done as rule at
speeds varying from 400 to 700 r.p. m,