[bmurph]

I got almost as much backlash as with the stock screws, and the backlash varies, as the nut travels down the screw. I don't know if it varied with the stock because I never checked it.

I have Roton ballscrews, and the play is 10 thou. with a little bit of wiggling to get there, like the balls are pushing into the groove, or something. The Roton website says the O.D. is 0.625, but mine are 0.612.

[hoss2006]

Repack the nuts with oversize balls and the backlash will be MUCH improved on these cheap screws.
Hoss

[ame=http://www.youtube.com/watch?v=bcjKULKKudw&feature=plcp]G0704 Roton Ballnut Max Oversize Balls - YouTube[/ame]

[MrWild]

Yep, my backlash is .0015 after oversize balls were installed.

[cameraguy]

Ballscrews have advantages, but reducing backlash isn't really one of them. It often increases it, actually. Especially cheap rolled ones, especially if you have just one nut. If reducing backlash was what you are after, you likely needed to look elsewhere.

You need to work with the configuration you have now though, so the suggestion of oversized balls are good advice. Also, remember if the bearings that hold the screws have any play, it isn't going to help any. Check the bearings and bearing blocks to see if they are the culprit. You could also fit a second nut to adjust preload if you can fit one in there I guess, that would solve most of your issue.

[bebob1]

what grade ballscrew

did you buy them new from roton

make sure you are measuring correctly. squeezing calipers too hard for example can make that off measurement

talk to customer service

[dang]

I didn't even use calipers. Encouraged by Hoss' documented works, I checked the data sheet for the ballscrew & nut and numerically determined what the largest size ball that I could fit. I packed the new ball bearings in and realized immediate backlash improvement, like night and day.

[bebob1]

would the backlash improve after operating for a while and allowed to warm up?

its like how they say you should let ur spindle dwell a little while before measuring tooll diameter or turning it off to then measure radial runout of the spindle by indicatoring it in. allows it to thermal expand a bit.

[hoss2006]

The major diameters of most screws (not just ballscrew) formed or rolled are going to be less than the stated size.
Roton calls them 5/8 diameter and not .625 for a reason. The OD is not that critical.
The balls run in the grooves not the OD. Mine were around .609 iirc.
Hoss

[bmurph]

I put the bigger balls on today, and got zero backlash in the middle of the x axis, and up to 2 thou at another section. I noticed that there's more stiffness as you put more balls in. I put 63 balls in the x.