with the spacer between them

As the width of the spacer approaches the width of the 5/16 rod, the paraxial
thrust at the POC will approach infinity by trigonometry, balancing the forces.

Bearing life is proportional to P*V, pressure times velocity. Find a derating
factor for off design loads, then keep the spacer thin to prevent multiplying
the forces too much.

At a spacer of zero, the load is all radial.

a pair of small plain
ball bearings(5mmx12mmx5mm) on the same
axel with the spacer between them instead of a each single grooved roller.

Yeah, but it's not exactly the same, is it, because there's this force, pulling
them apart. Now, you can just use a bearing mount type adhesive to glue the
outer races together, giving you a 5x12x10 bearing with a groove, because the
corners have chamfers. That would roll nicely on a square rod's corner, or on
the corner of an angle section.

You put a little pin through them when you are gluing them up to keep them
aligned. A firm press fit pin. Then you never pull, always push, to get them
off the pin, and then onto your axle. If you pull, they'll separate.

It's a preloaded design with preload no more than 10-15lb.

Um, in which direction? The weight of the traveller will load the rollers
tending to separate them. If the preload is inward, and more, and then the
weight increases they will go from being loaded in to being loaded out, with a
wiggle.

For cheap readily available bearings get the 8x15x6mm or whatever it is, which
are sold as skate wheel bearings in packs of eight, I think.

8mm is very close to 5/16.



Yours,

Doug Goncz, Replikon Research, Seven Corners, VA
Unpublished work Copyright 2003 Doug Goncz
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