Page 93 - Gear Technology Solutions

6.8 Summary

Gear engineers like to avoid undercutting, which is possible to some extent in
the early design stages by choosing the right amount of profile shift. However,
it is not always possible to eliminate undercut completely. In particular, if the
number of pinion teeth is below 13 the profile shift factor is often not sufficient.
If an undercut is detected, this shows that the additional room in the root fillet
transition to the flank is required for an undisturbed meshing process. This
undercut means that the base circle is above the root diameter of the pinion.
The top region of the meshing gear has a perfect involute which, however,
cannot find an involute surface in the pinion root for a correct meshing. The
undercut solves this problem partially by avoiding a metal-to-metal
interference. Such interference induces vibration and noise and creates small
scratches and surface damage which can lead to crack propagation with the
result of a tooth breakage.

If this undercut is eliminated merely by increasing the tool edge radius, an
interference will occur. There is a possibility to eliminate the undercut by
increasing the tool edge radius in combination with a correct dimensioned
topland chamfer of the mating member. Because there is no software to aid in
determining the required value of the tool edge radius increase and for the
required topland chamfer dimension, this process requires experience as well
as some trial-and-error loops.

6.9 Literature

[1] Stadtfeld, H.J. “Gleason Bevel Gear Technology, The Science of Gear
Engineering and Modern Manufacturing Methods for Angular
Transmissions”, Company Publication, The Gleason Works,
Rochester, New York, March 2014, Pages 17 to 19

[1] Stadtfeld, H.J. “Practical Gear Engineering, Answers to Common Gear
Manufacturing Questions”, Company Publication, The
Gleason Works Rochester, New York, March 2019,
Pages 107 to 108

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