The ISO and AGMA Gear Rating Committees have for several years been comparing the results of different
rating methods for several sets of gear pairs that have similar normal sections but different helix angles. The
analysis presented in this paper uses a very sophisticated finite element code that was developed specifically
for gear and bearing contacts to analyze the example gear sets. Analyses are also performed using a more
conventional load distribution analysis program. The results for the original gear sets show that the narrow
face width gear teeth twist significantly, thus moving the load to one edge of the face width and essentially
showing that the example gear sets are highly unrealistic. When analyzed by the ISO and AGMA rating
methods, the results do not reflect this twisting action. In an effort to come up with a valid comparison of
stresses for different helix angles, three adjustments using wider face widths were attempted. The first
scheme uses a wider face width with perfect involutes. Edge effects result in the peak stresses again being
near the ends of the face width. The second adjustment uses a wider face width but with a narrow load patch in
the middle of the tooth pair and results in the stresses increasing with helix angle. The third method, which
uses the wide face width teeth that have lead crown and tip relief, gives the most reasonable results, with the
root stresses being at a maximum in the center region of the tooth face widths. The paper compares each of
the results to earlier analyses performed by others using both the AGMA and ISO calculations.

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