Gear Cutting Tools

Explanatory notes
Hobs for internal gears are designed
for a specific gear. The
measurements for the maximum
and the minimum cutter diameter
and the maximum cutter width
must then be taken into account,
for which the internal hobbing
head is dimensioned.
ln the case of internal gears with
large profile displacement, the
maximum permissible cutter width
may be insufficient for cutting the
complete teeth, if the hob is dimensioned
in the usual way. It is
then necessary to fix the module
and the pressure angle of the hob
differently from those of the internal
gear.
On the hob, one tooth is defined
as a "setting tooth" and marked
accordingly. The cutter must be
positioned on the hobbing machine
so that the setting tooth is
when new placed in the "machine
centre". Although the setting tooth
will shift in the axial direction when
the hob is reground, it is not necessary
to correct the position of
the hob determined in the new
condition and fixed by spacers.
The hobs offered for finishing
internal gears are only to a limited
extent suitable for roughing. Bearing
in mind the tool costs, relief
turned hobs with a lead matched
to the workpiece should be used
for roughing.
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