[sp1nm0nkey]

I'm trying to come up with a flying optics system for a laser plotter. I'm going to be using very narrow timing belt to drag the carriage back and forth, but I'm not sure what to have the carriage slide on. Most people here discuss high load applications (routers, mills), but a laser optic suffers no load. What would you use, short of air bearings? I'm envisioning two quarter inch hardened steel shafts, perhaps narrower. Would you use delrin plain bearings, or maybe nylon? Oil impregnated nylon? Maybe oil impregnated bronze? I'm shooting for very low friction, and reasonably high accuracy. Thanks!

[jeffrey001]

I think I would go with linear bearing like these 10mm, shaft would be easy to find too, can go as small as 6mm I think.

4 X SC10UU 10mm Linear Ball Bearing Block CNC Table | eBay


Jeff

[sp1nm0nkey]

I see no reason to use linear bearings since there's little to no load, haha.

[jeffrey001]

This is not about load, it's about friction.

Jeff

[sp1nm0nkey]

Well, linear bearings certainly don't have particularly low friction in my experience, in comparison to metal on teflon or metal on delrin. They certainly seem to take load quite well, but you're pushing balls around races that are in a viscous fluid. Maybe I'm mistaken? I can stand an HSR20 rail vertically and the truck will stick, haha.

[ger21]

Well, linear bearings certainly don't have particularly low friction in my experience, in comparison to metal on teflon or metal on delrin.

Linear bearing should have far less friction than your other examples.

They certainly seem to take load quite well, but you're pushing balls around races that are in a viscous fluid. Maybe I'm mistaken? I can stand an HSR20 rail vertically and the truck will stick, haha.

Depends on your choice of lubrication, and the amount of preload. Profile rail bearings come in many different preloads. Also, end seas can cause stiction.
For your application, a very light oil lubrication is all you need. Actually, you can probably run them dry with no problems.

[harryn]

UHMWPE has very low friction, especially when lubricated with water, glycerine, or other very light oils. I am not really sure that it is less than a ball bearing system though.

[RomanLini]

Igus Brand "DryLin" teflon impregnated linear slide bearings on the Igus anodised aluminium rails. They will be less friction than balls on rails especially with the dust seals the ball bearings use. They have a good information resource online (or you can order a catalogue) if you need specs.

[BillTodd]

A little bit of friction that will act like a damper , reducing vibration in the belt, may not be such a bad thing.

Bill

[harryn]

I am not sure if it would work, but perhaps you could use a stiffer, wider belt, and skip the linear rail entirely.

If a belt does not work, then perhaps a simple screw could act as both the drive and rail.

Harry

[sp1nm0nkey]

Another belt won't work obviously because the thing isn't constrained and will just bounce and since this is an optical system, it'll lose focus. I can't use two screws because one of the original constraints for this system was speed! Screws are slow unless they're ball screws and then I might as well use rail and belt.

Igus rails seems to be the best way to go.

[harryn]

Hi, igus is fine, pacific bearings also makes similar setups.

I don't know how long your drive length is, but since it is a plotter, I assume between 10 and 20 inches.

Two 1/4 in round shafts are not very stiff, and a child can displace them with a finger.

A properly tensioned, 25mm wide brecoflex AT 3 or 5 size belt with steel wires would likely be in the same stiffness range for such a light load as an optical part. Try a test of it, you might be surprised.