Quote:
Originally Posted by sanddrag
With a hole .003 undersize, it'll do more than stay just in, it'll seize. That is far too heavy of a press fit. This will damage the bearing and decrease efficiency. A good medium press fit will have a ~.0004 interference. This will be sufficient to retain the bearing in most scenarios and will not excessively load it. A really tight press fit on for example, an R8 bearing into aluminum should have no more than about .0008 interference. These numbers come from my personal experience. Machinery's Handbook probably has some more standardized guidelines for designing bearing press fits.
As stated earlier, flanged shielded bearings are a good item to have around and use on FRC robots. The flange makes it so you don't need a counterbore or screws to retain it. Flanged shielded bearing part numbers follow the format FRXZZ. F for flanged, R for radial, the X corresponds to the size in 16ths of an inch, and the ZZ signifies double shielded. They are available for about $4 ea from Small Parts Inc (company specific part numbers brf-06 and brf-08) and from other sources such as VXB, Motion Industries, eBay.
Be careful when selecting flanged bearings. There are many unground non-rated flanged bearings out there. These can handle only a small fraction of the load and speed that ABEC-1 rated precision bearings can.
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Pretty amazing that our bearings our still turning then I guess
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At Engineer's Edge tolerances max are 2.3 thou on a 1.125 inch hole (R8 bearing O.D). Toss in some slop from the machine/jig and bam. From 7 ten thousandths over the maximum suggested tolerance to a perfect press fit in no time flat. Even without machine slop, straight measurement from one hole to its insert's O.D. we have done 3 thou. Funny thing is on a 1.125" hole that "good medium press fit" of ~.0004" is under the minimum interference listed.
I can't speak for any super high end bearings though, we stick at abec-1 (if that) I assume that doing 3 thou under for an abec-12 would be a big problem... but the tolerance on that bearing itself is an outlandish 50 millionths
Side note:
I think that if I ever asked a student or fellow mentor to machine a hole with a 1.1246" diameter hole, they would probably throw the print back in my face.
//edit
Here is what I wanted