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A design decision regarding the orientation of three bearings about a 3/4" bar.

I was going to suggest that myself... although for such a light load I'm not sure it'd be all that beneficial.
It won't.

I went to Alan Steel yesterday to buy more aluminum pieces after altering the design (again).
They have a cutoff saw with sliding table. I got curious about the rolling table. It's so heavy that it just lifts off the tracks.
In the picture the shaded parts are Delrin cylinders with a hollow in the center. One on each side of the bar and easily removable.
The metal cutting saw at the steel place was the same design, using metal wheels on the top. No bottom wheels.

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The wheel running on a round shaft has point contact. (read very high stress under load) Plastic tire will flat spot immediately. You will start with a snug fit and it will waller out in no time.
Yep, using this UHMW at .050 thickness as a tire around a bearing did get distorted.
The table is upside down. The top right side tire expanded and moved off the bearing.
Due to more force than designed because the holes in wood are not accurate.
I don't know if this will work well with metal parts.

Not for me. Just go to McMaster.com and look up 'linear ball bearings'. They are a common item and have been available off-the-shelf for decades (which means they competitively priced.) While you are there you can look up 'linear motion shafts' and find reasonably priced shafts and supports and whatnots. You can order a bunch of parts, get them delivered tomorrow morning, then assemble your device in less time than it takes to make the drawing and WAY less time than it would take to fabricate each bearing from regular ball bearings. McMaster Carr also has each component in a CAD drawing (or PDF) in just about any format you could care to use which also saves a ton of time.
I'm doing this now. I started this project with the idea that spare/scrap parts should be used. Up to now it's about 50% new.
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