Quote:
Originally posted by Patrick Wang
In the continuing quest to build a gearbox, yet another question has popped up. (perhaps these threads will turn into a gear FAQ?)
I've been looking around for people who sells gears. Mainly McMaster and BERG. What I've seen in the Mcmaster catalog however, is that their selection of gears of 20 degree pressure angle seem somewhat limited. Now their website states that the 20 degree pressure angle is a new AGMA standard for higher torque carrying capabilities, but they don't seem to offer any plain steel 20 degree spur gears under 24 pitch.
BERG on the other hand, has a much greater selection of gears.
My Question, mostly out of curiousity and to see other people experiences, is
-How significant is the difference between the older 14.5 degree pressure angle gears and the 20 degree gears.
-What pitch gears have you used, and how were the results?
The original plan was to use 20 pitch gears at 20 degree pressure angle, but I am having problems finding one with a finished keyed bore. (our machining resources are limited)
I have however seen that Mcmaster sells 14.5 degree pressure angle gears with finished bores, and am looking for a viability in them.
Thanks again all!
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So many questions in a single post! But I'll try to get around to them all. First, for off-the-shelf variety it is hard to beat BOSTON gear. They make all of the gears sold by SPI and many, many more. You also might want to check out
http://www.globalspec.com You can spec your gear here and it will search a bunch of on-line catalogs (including BERG, but I don't think Boston) and identify any close matches. One caution, there are several custom gear houses that will tell you they have ANY gear, when they really make it up special, just for you. They will invariably show up on the match list. You can specify whether or not to have keyways on your gear.
For our purposes I don't think pressure angles matter much, as long as they match. A 25 deg gear with a 14deg gear just won't work too well.
What pitch works for a given load is very material driven. You can get away with a lot in steel that you can't in bronze or plastic. On the other hand, if you can't get steel, you might be able to reduce the pitch of a bronze gear and do it that way.
We have not yet built our own gear box, but it's definitely in the works for next year. A few years ago we built a gear driven arm though. I think the gears were close to 20 pitch cast iron, but I'd have to look it up at home. They were certainly in the SPI catalog as that's all we were allowed to use back then. They had a pretty major load, but we never failed a gear tooth. We broke plenty of other things, but not gears.
One thing I found out from working with gear design formulas. Used straight they tend to way over design things. That's because they are set up to do things that will run for many years and millions of cycles.