October 12, 2022
We cannot leave our lesson about tooth depths without covering bevel gears. There is a tendency to think of bevels and worms as being best left to specialists, but a true gear guy or gear gal needs to understand that they are not some secret cult that defies our understanding. A Gleason engineer on the AGMA Helical Gear Rating Committee once, in total seriousness, insisted that helical gears were simply “spiral bevel gears with an infinite cone distance.” Stunned silence was his reward; we all needed to process that idea before realizing he was right. What is different are the two prevailing “systems” of bevel gears; Gleason uses a tapered tooth depth while Klingelnberg employs a constant tooth depth. When Klingelnberg designs first came to the United States there was considerable “discussion” about whether their teeth were stronger than Gleason’s. I put “discussion” in quotes because engineers can have such strongly held opinions on some topics that reasoned argument turns into a regular barstool argument. This is completely understandable in light of the huge investment in plant and equipment. Bevel cutting machines, even the early ones, are amazingly complicated devices with lots of moving parts — parts that require precise adjustments and very skilled designers and operators. For many years the calculations were so complicated that the entire domestic bevel gear industry relied upon Gleason to provide the “cutting summary” needed to make the machines work. Even more shocking was that our technical contact at Gleason, a contact shared with competitors, was a WOMAN. I throw that tidbit in just to illustrate for younger readers how backward we were to find a female engineer to be unexpected. But I digress; eventually calmer, more reasoned discussion returned to the arena and today we recognize that both tapered depth and constant depth bevel teeth have their place. The rating formulas treat them equally. And computers made it possible for companies to calculate their own machine settings.