Thread: Backlash
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Unread 03-06-2008, 00:02
sanddrag sanddrag is offline
On to my 16th year in FRC
FRC #0696 (Circuit Breakers)
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Join Date: Jul 2002
Rookie Year: 2002
Location: Glendale, CA
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Re: Backlash
I would speculate that you want your center to center distance increased by at least the amount of tolerance of your machine to ensure your gears do not bind. If your machine can only hold .003, I'd say either look for a better machine, or increase your center to center distance .005 over nominal. I'd be weary of going with any more than that though.

For the bearing fit in aluminum, you certainly don't want any more than .001, with something in the range of .0005 being optimal. More than probably .0015 and you'll start to excessively load and potentially even damage the bearing. There are formulas to calculate this, but this is a basic rule of thumb based on experience.

Make sure you use precision ground ABEC rated bearings. If you don't, you'll certainly have problems. Unground and/or non-precision bearings are not rated for anywhere near the speeds, loads, or tolerances of precision ones, by a factor of up to several-fold. I too would recommend through holes and flanged bearings. The most common bearings to use in FRC gearboxes are FR8ZZ and FR6ZZ. These can be obtained from a variety of sources, including Small Parts at about $4 each, under part numbers BRF-06 and BRF-08. There are also cheaper sources. Check local suppliers.