Most of the gearboxes I have been involved with use single helical gears. Its excellent power capacity per mesh makes it the default system for many designers. Every aspect of these gears is studied and tested in great detail by standards committees and development labs around the world.
My first assignment for AGMA was to attend a Helical Gear Rating Committee gathering in early 1979, when that group was finishing up a major re-write of the American method of rating spur and helical gears. It was like attending a graduate seminar with the top people in the field cast in the role of “asker of questions everyone else is too polite to ask.” The experts were very kind and patient with the class dunce; I remained somewhat involved with the committee until 2018.
There are still things for me to learn about gears, but helicals are one sector that I believe I know very well. One of the things I started learning in that initial meeting is that there is no consensus on what is the proper design for a helical gear set. The sages I learned from did not agree, and I do not expect to convert any of you to my point of view in a few blog postings. And I am OK with that. My goal in the next few postings is only to discuss some of the major areas of disagreement and give the reasons I do things the way I do them.
I will start with a pet peeve: the pronunciation of the word “helical” itself. I am firmly in the “hell-ick-al” camp; the “heel-ick-el” pronunciation is like squeaky chalk to my ear. I first learned the first pronunciation as an apprentice and questioned the other once I left the “mother ship.” Helical is derived from helix so I can see where some might think the latter is valid. We do not say “heel-e-o-copter,” though, so I will continue to cringe whenever I hear that second pronunciation. End of curmudgeon rant.
The “helix” angle is the obvious difference between a helical gear and a spur gear. The more you learn about them, the more you realize that a helical gear is much different than a “spur gear with crooked teeth.”