Tolerance/fit question

Oct 21, 2017 2 Replies
P

I am turning a ballscrew end down, to fit a 6mm dia bearing. The bearing will be ABEC7, which has a hole tolerance of 0 to -4 microns.



So far, so good. But how big should I make the shaft?



It is 6.000 mm now (yes, to +/-1 micron :o), but normally I'd turn it down a bit more; I don't want to have to heat the bearing to get it on/off, a sort of medium interference fit will do.


I have been googling, and there are tables of tolerances, and pages with recommended fits, but I haven't seen one page which actually recommends an actual size or even what a normal type of fit is in terms of tolerances - maybe my google-fu, or perhaps my engineering-fu, or both, is weak today.


Thanks,



Peter Fairbrother


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M

You don't want to reduce it below 6.000mm. Doing so brings the risk of a slightly sloppy fit. With the bearing tolerance and the measured shaft size,

press on at that sort of fit, but will be a hand (clean handkerchief for

that temperature.

regards

Mark Rand

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P

OK, I'll go with that for now, just round off the end edge and cut the slot for the circlip. Thanks.

I was a bit worried, it took me hours to get the ballscrew chucked with sufficiently concentricity and [parallelness of the axes of rotation and ballscrew, whatever that's called], and I didn't want to take it out of the lathe and disturb the setup.

On reflection that worry was a bit pointless, as I am using carbide paper for the final finishing-to-size, and I could just rechuck it any-old-how and hold the paper in my fingers ..

ah well, thanks anyway.

-- Peter Fairbrother

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