Bearings Help

[Cartierusm]

I've got a piece of Aluminum with a 3/8" through hole in it and a pocket at each end to hold a 1/2" OD 1/4" ID Ball Bearing and another round part with a 1/4" hole in it is bolted onto the bearing part so it can rotate. I noticed when I tightened it that of course it was tight and could not spin. At first I though that I need some bearing washer for the inner races of the ball bearings and that worked better but still couldn't get it tight, and I mean just snug not super tight or anything.

So the question is for this type of application should I use thrust bearings or should I put a 1/4" ID by 5/16" OD to hold the inner race where it should be? I figure no matter if I'm using a bearing spacer for the inner race if there is nothing behind it hold the pressure it will just deform or pop the bearings out.

I would like to use hte ball bearings as I already made the part and pockets so if I do use a sleeve how do I get it to be in perfect tolerance with the spacing of hte outer race. Should I make it just shy of the depth of the outer race then use inner race bearing washers to get it exact? If this is the correct way then how can I tell if both inner and outer races are both contacting with the same amount of pressure if I can't see the inside?

Thanks.

[JimBoyce]

First get rid of your perfect tolerance idea.
Virtually all bearing shafts or sleeves have one bearing that establishes thrust position along with radial support. The other bearing is for radial support only.
An example is an automotive alternator which has a ball bearing in the front for radial and thrust position, and a roller bearing in the back for radial support. The shaft can expand & contract and move slightly end wise on the roller bearing.
Machine spindles usually have a front bearing (consisting of 2 or 3 ball bearings) that gives radial and thrust position and a rear bearing that can slide end wise for heat expansion.
It would seem to be difficult to lock the OD of one of the bearings to establish end position since these parts are already made, so go with the 1/4" x 5/16" spacer sleeve.
A spacer about 0.001" to 0.002" longer then the inside dimension of the bearings should be OK. Using shims to fine tune to get a nice rotating feel on the roller should work good.
Do not attempt to get the bearing ODs and IDs exactly the same, it is impossible, and heat expansion will ruin it out anyway. In other words .001" or .002" slop is necessary.

[Cartierusm]

Thanks, that's what I thought. I did that today on another part and got it pretty tight and still rotates freely.