Mounting Distance
The correct setting or adjustment of the
pinion at assembly is most important. Provision should be made for
adjusting both the gear and pinion axially. It is advisable to first
adjust the pinion to its correct mounting distance (See
figure 28),
determined by measurement or by a gage centered on the gear shaft or
a "dummy" shaft made for this purpose. The gage may be
arranged to measure from the center of the gear shaft to a flat on
the extreme small end of the pinion teeth or to the back face of the
pinion hub. After the pinion has been correctly positioned, the gear
should then be adjusted to mesh with the pinion to obtain the
desired amount of backlash.
The shims used in adjusting the gear and pinion
location, and the bearing preload, should not be less than
0.015" thick and should preferably be on the stationary member
of the bearing.
A means of inspecting the gears in mesh is desirable both from an
assembly standpoint and for periodic check. An inspection hole and
cover should be arranged so that the contact pattern can be observed
on the teeth of both members of the gear set.
In storage or during shipment lapped gears should
always be fastened together in pairs or sets, and they should not be
separated until ready to assemble.
Backlash
Bevel gears should be manufactured and
assembled to have a definite amount of backlash, which varies
according to pitch and operating conditions. Backlash is necessary
for safe operation. If gears are set too tight they will be noisy,
wear excessively, and possibly scuff the tooth surfaces, or even
break.
Figure 27 shows the ratio at which the axial movement of
either member affects the backlash.
Figure 26 suggests the recommended normal backlash at tightest
point of mesh for gears assembled, ready to run. The backlash values
etched on ARROW gears are derived from this table and apply to the
tightest point of mesh. (See also
Figure 29). In many instances,
these limits will require modifications to suit the special
conditions of operation.
