[andy1989]

Has anyone used the cheep non branded mgn linear rails you get on ebay for a cnc router?
I ordered a couple last year initially for a 3d printer build but they have far to much resistance for small nema 17 motors belt drive and fast speeds. For a cnc with nema 23 rack n pinion and generally much slower speeds I think they will be okay.

Some input from anyone who has used them for a cnc would be great.

This is an example of the rails I was thinking of using.

Look at this on eBay http://www.ebay.co.uk/itm/282372584798

[alan_3301]

Do you think they were binding, or did it seem like they had a high preload?

[handlewanker]

Hi, the MGN in the title refers to the size coding.......what it means I don't know, but it has a number after it that gives the width of the rail.

The 15mm wide one I bought for evaluation had a plastic strip in it to keep the balls from falling out......I removed the strip and the balls fell out on one side.......easy to replace.....a bit of grease helps to keep them there.

I found the bearing block had a few gritty sections on the rail and it was fairly stiff to slide up and down.

If the design has all the balls of the same diam this will cause crowding and friction as the balls rub against each other and so cause friction.

I haven't measured the diam of all the balls but if they are different diams..... such as .02mm undersize for half of them, then I suspect the balls must be inserted with alternate small and big sizes to enable the smaller size balls to act as spacers and not make contact with the tracks etc.

For the price don't expect high precision, but they might do an adequate job..........I'll just have to do some more tests.
Ian.