Bearing fit and related questions

[mjr6550]

I have an old 6x48 bench belt sander that I recently picked up. Since it was very dirty and had not been used for quite awhile I decided to take it apart to clean and paint it. In putting it back together I was wondering about bearing fit. It has a 5/8" shaft with ball bearings around 2" O.D. The bearings are pressed onto the shaft. At one side the bearing fits into a bore in the cast iron with a very close slip fit (I have not measured it). The other side fits into steel sleeve that fits into the casting. The sleeve is held in place with a set screw into a groove on the od of the sleeve. The bearing is a loose press fit in the sleeve and held in place by a shoulder and retaining ring.

My questions are: is there any concern that the bearing directly in the cast iron bore would spin? I guess with minimal friction thus is not an issue. I also assume the bearing will run hotter than the cast iron and maybe tighten up. This got me thinking about locking the bearing in place, but then I questioned how this is normally done. Thermal expansion would put a lateral load on the bearing. Maybe not too bad with an 8" long shaft, but I assume this can be an issue at times.
Sorry for the long post.

 

[Milland]

This is a "don't worry about it" situation. It's a terrible environment for a rolling element bearing, but the one that was in the sander previously survived, right? And didn't spin in the bore?

At worst, fairly quickly some grit will migrate into the area and help lock the outer race in place.

 

[Phil in Montana]

If you are concerned use a drop of locktite, as a belt sander you will not wear it out...Phil

 

[Terry Keeley]

I just replaced the bearings on a Baldor carbide grinder and IIRC they were mounted the same, press fit on the shaft, one loose in the housing and the other fixed for axial position.

Think it's a pretty common arrangement for motors, machine tools etc. to allow for expansion.

 

[mjr6550]

Thanks for the replies. I never thought about it before. I thought bearings were typically locked in place, but then I thought expansion may be a problem. The bearings seemed fine. They were made in America, so may very well be original.
It was covered in sawdust. My intention is to use it mostly for metal, so I may not have as much luck. At one end the bearings are pressed and recessed into the aluminum belt roller, so I think I will put some foam inside the roller as a shield. I think I will try to shield the others also, but not sure how yet. I want to shield the motor also. It looks like it swallowed a lot of sawdust.

 

[Peter from Holland]

With bearings the spinning race should have tight fit while the stationary race should have a slip fit
Peter

 

[NC Rick]

I just finished reworking the bearings n a small vintage drill press spindle we will use for drilling orifice's we do. The bearings are also on a .625" shaft. I have a slip fit on the od of the bearing and a 0.0001 - 0.0002" fit to the shaft. The bearings need to be pressed on to the shaft. Bearings are designed for one side to be pressed for proper tolerance.

 

[NC Rick]

Oops, from Holland, I should say that on that diameter shaft you would like something like a 4 micron interference fit ;-)