Helical and Cut Spur Gears and Gear Solutions

If you haven’t had a chance to check out Gear Solutions magazine or its website, we at Gear Motions highly recommend it. One of the most excellent parts of the magazine is the “Tooth Tips” section written up by William Crosher. Crosher doesn’t dumb down the language for non-engineers and gives solid technical advice alongside relevant current industrial data. A recent article in Gear Solutions by Crosher talks about the importance of roughness and surface finish as they relate to the longevity and effectiveness of a gear assembly in both spur gears and helical gears. Without getting into great detail (he does, you can read the article if you want to get the full scoop), his basic point, in his own words, is as follows:

“There is no relationship between gear quality and surface finish in AGMA standards. An AGMA document on gear tooth surface texture (AGMA906A94) is a guide to surface finish. Unfortunately, there are still many who do not realize the significance of the surface finish on tooth flanks and believe -quite incorrectly- that it will be a self-correcting condition. Tests have indicated that the rubbing of any two surfaces reduces the initial roughness by no more than 25 percent.”

Another point Crosher makes is that accurate gear sets including cut spur and helical can have surfaces with deep valleys, (sometimes called scallops) and it’s important to remember that flank surfaces should be measured in one direction – going from the tip to the root. Crosher’s article in Gear Solutions is important because it also discusses the need for standardization these processes by AGMA, while giving logical assessments of the importance of measuring roughness and surface finish in a quality product.

If you have an opinion or any comments or questions about the differences in helical and straight cut gears, we’d love to hear from you. Contact us today!