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Figure 5: Qualitative influence of center distance and shaft angle changes

21.7 Summary

Cross-axes, helical gears have point contact and their surfaces are subject to
high surface stress. The point contact can be explained with the orientation
between generating rack, pinion and gear. A low transmission error can only
be achieved in low load condition. Also, the center distance insensitivity of spur
and helical gears does not apply for cross-axes helical gears as illustrated in
Figure 5 (left). However, the opposite characteristic can be seen regarding
shaft misalignments. Spur and helical gears without length crowning react with
high transmission error if the shafts are misaligned. Cross-axes helical gears
offer a “natural” length crowning, which reduces the sensitivity to small shaft
angle changes (see right side diagram in Figure 5).

21.8 Literature

[1] Niemann, G. “Maschinenelemente, Band 3”, Springer-Verlag, Berlin, Heidel-
Winter, H. berg, New York, Tokyo, 1983, Pages 67 to 70

[2] Shigley, J.E. “Mechanical Engineering Design”, McGraw-Hill Book Company,
Mischke, C.R.: New York, Tokyo, London, Hamburg, 1989, Pages 548 to 549

[3] Stadtfeld, H.J.: “Ask the Expert - Worm Gears”, Gear Technology Magazine,
October 2013, Pages 51 to 52

[4] Stadtfeld, H.J.: “Ask the Expert – Relationship between Misalignment and
Transmission Error in Cross-Axes Helical Gear Assemblies”, Gear
Technology Magazine, March/April 2019, Pages 44 to 48

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