Cheap ballscrew runout

First I have to say it's annoying the only DIY section is in the woodworking section. I wasn't sure to post here or in the general metal workign section. Since I have a metal cutting machine I wasn't sure because people here might be more familiar with using the cheap DIY components but people in the metal section are going to have a better familiarity with the forces and stresses my machine will see.
So anyway yes I have a CNC machine I built myself. I cut mostly aluminum, do a little wood and plastic and have tested a couple small projects with stainless.
I used the common china no name ballscrews like this.
http://d2elpw2msxzjrq.cloudfront.net...252968d9a1.jpg

When I first got them they had a more than acceptable amount of backlash. A few months later and they have about .3mm backlash. I did a lot of searching and cannot find posts of others with the same issues or discussion on ways to tighten them up. This has me wondering if this is a common problem from regular use or if this is more due to the fact that I have stuffed the machine a few times and or the fact that I am pushing it hard cutting aluminum? Have others had this issue with these ballscrews?

Is there a more affordable screw that will hold up better?

My other thought was maybe to order another set of these and then using two nuts on one rail and making something that would allow a spring to keep them tensioned against each other in a jam nut fashion. I would hate to do this only to find out they quickly wore out fast enough to make it not worth the effort. Or seeing if there is a better bang for the buck option.

yoshimitsuspee

You can re-ball them with a bigger Ball, they are as you said a low cost Ballscrew, so this is to be expected, they range in grade C7 to C11 spec so you can't expect to much from them, in you case the best would be to measure the Balls & get some new one's a .0001 /.0002 bigger & reassemble with using ( 1 ) new Ball & ( 1 ) old ball & see how that will work, if it is still loose you will need an even bigger set

If you could measure the inside Ball groves in the Nut & the screw then you could calculate the right size balls to use

You can buy just the Ball-nut,if you wanted to use ( 2 ) but you would need to get it from the same source/manufacture

If this backlash showed up abruptly, it might be that crashing the machine has jarred something loose in the ballscrew supports, rather than an issue with the screw or nut itself. Try wiggling things and see if the screw moves slightly back and forth.

Are you using Chinese bearing blocks? The bearing blocks are **** and often it's the oil seals that actually seem to reduce backlash. The angular contact bearings are not preloaded and need shimming.

The bearing blocks are crap. Mine came with regular radial ball bearings, though they only have around 0.003" of endplay. I'm sure it would be much more under a greater load.

"Only" .003" of endplay??? With proper preload on an angular contact bearing there should be "0.000"" endplay.

Dick Z.

Yeah, that's what I would expect.
I guess it seemed I was ok with that amount, which I am not.
I would like to get proper AC bearings on there, just need to find out what to get, and how to assemble correctly.

Mcmaster plastic round shims work great for preloading between the AC bearings in my RM16 end supports.

McMaster-Carr for $14.87
p/n: 98090A964 is an assortment of sizes in 1.125 OD 0.75 ID round plastic shims.

0.3 mm wear in the ball nut?
Frankly, I find that a trifle hard to imagine in under 10 years. It would represent a huge amount of wear!
And that is NOT a 'cheap' ball screw/nut combo anyhow.
Nope - I don't believe it.

How did you measure this backlash?
Have you checked that the ball nut is securely mounted?
Have you checked the end float in the main bearings?
Have you checked that the motor is securely mounted?
If there is a belt drive, are both the pulleys securely mounted on the shafts, and is the belt tight?
If there is a direct coupling, is it secure?

To be sure, you can replace the balls or put in a second ball nut - but I can't help feeling that the problem might be something else just loose.

Cheers
Roger