| Michael Hill |
08-04-2016 15:58 |
Re: Gear Teeth Clearance
Quote:
Originally Posted by Billfred
(Post 1569654)
I know the additional .006" is some fudge factor, effectively trading gear life for less friction in operation. But the number I'd learned from oral tradition* is .003" or so. What are the benefits of adding the extra distance?
*Even before I learned this from other FIRSTers, I knew a variation on this from racing R/C vehicles, which have a similar opinion of gear life vs. speed**; there, the conventional wisdom is to run a piece of paper between your pinion and spur gears to ensure "proper" spacing--and a piece of paper is about .002" thick.
**If you haven't gathered from the "racing" part, they skew towards speed.
|
Extra distance will buy you more tolerance in manufacturing at the cost of more backlash. That said, .003" we usually use. Vex gears (the ones we usually get for custom gearboxes) are AGMA 11 quality, which means their total composite tolerance is < 0.001" for all gear sizes ( http://www.americangearinc.com/quality.html). You could get away with 0.002" spacing, but you're leaving yourself with no tolerance for the manufacture of your gearbox plate. Our gearboxes are cut by either waterjet or CNC mill, so we can hold somewhat tight tolerances. However, Even if the waterjet was slightly out of tolerance, it's still probably fine because it (should) be unlikely that both gears are > 0.0007" too large. Additionally, you'll get a bit of wear that makes things run fairly smoothly. |
