Your drawing has "Leading Composites" in the title block. Is this an enquiry to help a commercial firm?

Edited By Jeff Dayman on 29/01/2021 18:32:03

You need something with a similar coefficient of thermal expansion to the body of the roller.

Martin C

Edited By Martin Connelly on 29/01/2021 21:45:55

You don't, hence why you leave one bearing floating. Just like the rear spindle bearing on many lathes.

If the roller is a plastic like nylon it'll have 2-4x the expansion rate of aluminium so it's just not practical.

Is there in fact any need for an internal spacer. If the two bearings are a press fit into a recess at each end of the roller surely that should be sufficient to maintain lateral alignment. The axle will similarly align the bearings axially. I am sure it will work without the internal spacer (I stand to be corrected).

John

It obviously depends upon the installation … but I would guess that the bearings are intended to be not loaded

i.e. the inner races are clamped tightly [between plates, or whatever] and the outers are ‘floating’

That way, the differential expansion of materials is accommodated by the axial play in the bearings.

MichaelG.

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Edit, for clarity : I see the item as being an idler [perhaps a belt-tensioner]

Edited By Michael Gilligan on 30/01/2021 10:15:17

Just for further info the original is an aluminium idler wheel for a knife grinder / belt sander.

The picture makes it fairly clear that the spacer is probably a steel tube.

John

It is the same with eg car wheel bearings. My MGBGT front wheels bearings have an inner spacer and special 'pick off' shims to allow the bearing nuts (2) to be done up tight without putting pressure on the rollers and setting a precise runout. None of my trailer bearings have this and it is just a case of do it up, back off a bit and use a split pin to hold the nut.

For a belt sander such care should be of little value but can be used to give a false sense of quality to something that is about the same a conveyor roller mass produced for a couple of quid. If the mounting is crude and allows someone just to keep tightening a bolt putting pressure on the bearing then a spacer protects against numpties. I think in this application I would put more emphasis on being able to replace the bearings easily as the abrasive dust will keep getting throught the seals.