Basic bearing/shaft fit question

Since the load direction is constant relative to the non-rotating inner race, the fit isn't very critical. A close slip fit is fine. If you go by the bearing books the shaft should be 4.996/4.988mm.

Easiest thing, if you're attaching the bearings to the sides of flat fingers, is to not worry about the fit and just fasten them with M5 socket heads and a shim under the inner race so the outer doesn't rub. A little fussier would be to use 5mm precision shoulder screws.

Thank you for the recommendations Ned. Just what I was wanting to know. Bill

While others have answered your fit question, you might want to consider one of the problems with ball bearings on the steady rest fingers. (Or more so on follower rest fingers.) That is that the fingers will simply sweep chips aside, but ball bearings risk rolling chips into the workpiece, spoiling the finish -- or even moving it momentarily off center, thus spoiling the finish by causing the cutting tool to dig deeper or back off.

Just a consideration -- so make it easy to disable the bearings at need.

Good Luck, DoN.

I only use ball bearings on rough stock in the steady rest, and only then in order to put a center in the stock so that I can support it to machine a good surface for pads. Besides the chips being rolled into the stock by ball bearings the bearings will also reduce the diameter a bit where they are rolling, leaving a depressed band on the work. For steady rest work I have a drip oiler mounted to the top of the steady so there is always a cushion of oil between the pads and the work. This prevents marking of the shaft, makes things run cooler, and won't cause chips to be pressed into the surface of the work causing dents. Eric

Thanks for the advice DoN. I think I just "locked" onto the original design for this rest without thinking; but the more but I think about it, making plain fingers sounds better.

Thanks eric, I'm going to do as you, and DoN, have suggested. Bill