The Old Family Recipe

Continuing with bevel gears…

As a beginning gear guy, I was very content to leave the bevel gear design to the experts. If my employer did not have a bevel cutting department, it was simply a matter of avoiding right angle gearboxes or using something “off the shelf” from the companies who had catalogs. Then I took a job where they not only had bevel cutting machines — they expected ME to be able to design new sets whenever there was a need.

A quick look at the bevel gear rating standard just about gave me a panic attack. Fortunately someone at Gleason took pity on me and provided copies of Gleason’s “Standard System” books for both straight and spirals.

Unlike other gears, bevels do not have a cutting tool that is tooth depth- or pitch-specific. While all gears are “scalable” or “parametric,” to use the more modern term of art, only in bevel gears can you use an “oddball” pitch without having to acquire a custom cutting tool. A “point width” and “point radius” are specified on the cutting summary based upon tooth size at the small or “toe” end of the tooth; the set-up technician selects it off the cutter shelf.

The standard system books did the hard work for you. Page after page of charts are included for various tooth combinations with the needed angles and dimensions. The angles do not care what size the teeth are, but you have to divide the charted dimensions by the pitch needed to get the outside diameter and rating you require for your specific application.

It eliminated the need to do any math beyond long division, but the formulas used for each feature were provided in case you were one of those engineers who have to check everyone else’s work. Designers needed only a couple of photocopied pages of “I” and “J” factors, and they were ready to calculate ratings. The small print recommended a “maximum” face width and you needed to select a few “influence factors,” but there were not that many options to confuse you.

I do not know if Klingelnberg or Oerlikon has ever published a similar “system book,” but look forward to learning more about their practices. There has to be more than the guidance found in Gear Design Simplified.

About Charles D. Schultz 489 Articles
Charles D. Schultz is President of Beyta Gear Service and one of Gear Technology's technical editors.

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