Matching bearing for rotary shaft

[sh2005]

Hello all,
I will start by saying that this is my first practical hands-on work with bearing, so my questions may seem amateurish.

I am working on a machine design that will have a rotary shaft driven by an electric motor (~ 2 hp) via belt - nothing exotic. I have bought a 5/8” keyed shaft and (naively) assumed that ball bearings that have 5/8” ID will have a press fit on the shaft. When i tried the 6202-5/8 bearing and another same sized one with snap ring, the bearings were too loose - they freely slide on the shaft. Measuring the shaft with a digital caliper, shows the shaft is 0.623”, .002 undersized. The vendor where i bought the shaft from doesnt publish the tolerance, but i looked in places like mcmaster-carr and it looks like that is within the tolerance for this kind of shaft.
The vendor for the shaft suggested pillow block bearings with set screws. I had originally planned to use pillow block bearings because of ease of mounting, but using those makes the design bulky, and i want to try out an idea i have for mounting radial bearings. Besides, in my mind, i have assumed that press fitting is better than mounting the bearing with set screws because the holding force of the press fit will be greater. My assumption can be wrong, so i am reaching out to you for that as well as the following questions i have:
1. is there a standard off the shelf ball bearing that will have a press fit on the shaft i mentioned above? The published ID/bore i have found (like skf’s website) for bearings like the r10 series are 0.625”, so i am not sure about their exact dimension, tolerance and fit. Or is insert bearing my only option?
2. Is it even a good idea to mount a shaft with keyway in a bearing with press fit? The shaft i have has the keyway for the full length and there will be a gap under part of the inner race of the bearing. Frankly, i havent seen any pic online of that, so not sure if that works or not.

The shaft doesnt have to be 5/8”, but the other parts of the machine have 5/8” shafts so i wanted the use the same size here.

Lastly, I dont have the equipment or skill to turn/mill a shaft myself, so i have to do with standard off the shelf parts.

Once again, the answers probably are very obvious, but i dont have much experience to go with. Thanks for the help!

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[Jim Dawson]

Normally you don't really want to rely on a press fit for axial location of a shaft, normally you would use snaprings, threaded fasteners, flanges and/or shoulders or shaft collars ( https://www.mcmaster.com/6435k15 ) . But under some conditions it might work OK with a press fit.

There are no stock bearings that are undersize, if it says 0.625 in the book, it's going to be 0.625 +/- 0.0001 or better.

In this case I would use High Locking Strength LocTite (Green) https://www.mcmaster.com/loctite to anchor things together, but it depends on how much axial load is on the shaft.

[sh2005]

Jim, thanks for your reply. Yes, I am planning on using shaft collars and, if needed, thrust bearings, to axially locate the shaft on the bearing But, my main reasoning to have the bearing be press fit so that the bearing's inner race rotates with the shaft. With a very loose (slip) fit, the shaft rotates inside the inner race, so at that point, the bearing is nothing more than a plain bushing.
I considered using Loctite or 3M's structural adhesives (like DP420) but it seems like not the ideal solution, so I am keeping it as last resort.

I can use insert bearing (without the pillow block), but I am curious to if those are inferior to regular ball bearings, in terms of "holding force" (not sure what is the proper term) between the shaft and the inner race? Ball bearings seem to be used lot more than the insert bearing, but is more because of the cost?

Also, am I overthinking about the holding force? It seems to me, theoretically, as long as tit is greater than the total friction between the two races in the bearing, the inner race will turn with the shaft.

[Jim Dawson]

Mounted/insert bearings are very common in industrial applications. They are normally secured to the shaft with set screws or other locking methods, and are quite a robust locking system. Press fits are normally used in gear boxes and things like that. The shafts are sized to press fit into the bearings.

For ease of assembly, stock shafts are slightly undersized for a slip fit. Loctite bearing mount products are your best option here if you use non-press fit or a non-locking insert bearing assembly.

If you don't have the machine tools to turn your own shafts, you will have to use off-the-shelf stock parts.

[sh2005]

Hi Jim,
Thanks for the confirming what i was thinking.