I have a lot of hardened steel rods from photocopier teardowns.

3D Printing
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1

I have a lot of hardened steel rods from photocopier teardowns. They measure 5.9, 7.9, 9.9, 11.9 mm. As you probably know the standard linear bearings are too sloppy to use.
Are there any bearings I could use that are suitable for this size rod? Preferably with the same dimensions as the standard 6, 8, 10, 12 mm linear bearings.

2

Delrin will slide very smoothly, or IGUS material, suggest make your own. can work far better than bearings. Not kidding, i have 2 prototypes that run on delrin and are just butter smooth and perfectly accurate, zero lubrication and self cleaning as well. I use extrusions and 2 opposing delrin rod sections at the top and bottom of carriages, just like wheels but no wobbles or multiple moving parts just low friction sliding. 3 delrin sections at 120 degrees in a printed mount that clip on your rods will work great, I promise. I can see the design in my head and from my experience with delrin on aluminum extrusions 3 around a smooth rod would be even better. 3 top and 3 bottom spaced with a 1:2 ratio cantilever of the belt mount to the rall contact, no stiction and good to go. 6 per side, 2 rods so 12 points of contact but with smooth rods and light pressure, it will just glide. Send me a few rods I will design it for you in the sizes you need based on simple diameters, much easier than extrusion slots I am sure.

I need to tear down some machines, live in a city where I probably could access rods like you describe for free from office castoffs…

3

There are bushings with adjustable preload. Basically a bushing with a small slit on the side, they get press-fit to the final dimension.

4

You might find that linear bearings made for imperial rods may have less slop. The difference isn’t huge but the imperial linear bearings are just that little bit smaller, and they can bind on metric rods because they’re a touch too small. eg: 5/16th of an inch is 7.9375mm.

5

Additionally:
15/64" is ~5.95mm
25/64" is ~9.92mm
15/32" is ~11.91mm

6

My calipers only have one decimal place so I don’t have exact measurements. Could be imperial I guess.