[nc_machine09z]

I bought a ground ballscrew on ebay, with two ballnuts, supposed that ballscrews have hardly any backlash,well when I turn the ballnut back and forth, I notice some play between the ballscrew and ballnut,about a quarter of an inch, is this normal, or this ballscrew is broken, this is a nsk ground ballscrew with two ballnuts, I don't know much about these, thanks.

[awerby]

What do you mean by "play"? If you can move the nut(s) 1/4" up and down the screw without turning it (them), then something is seriously wrong. If something else is going on, tell us about it in more detail.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[packrat]

To be "backlash free" the nuts have to have a spacer or spring between them. If using a spring, it has to have more force than the object being moved by the screw.

A ground ballscrew in its self is NOT backlash free. The ground ballscrew only means it may be (but not always) more accurate than a rolled ballscrew.

[nc_machine09z]

ok I hold the ballnut with my hand and it moves a little before I start turning, if I move it back and forth it moves a little, I don't know if you understand me, but I have another ballscrew with the ballnut and it doesn't move at all when I try to just barely turn it, it has no play at all, thanks guys for your patience. this ballscrew is 60 inches long and has a double ballnut 7 inches long, 1 inch screw.

[awerby]

See if there's an adjustment in the double ballnut that takes up the backlash. Often you can revolve one nut against the other to preload them. If they're too loose, you get backlash and if they're too tight the screw won't turn at all. You want something in the middle. If there's slop and no adjustment possible, then send the thing back, or try claiming against the ebay "buyer protection" guarantee.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[nc_machine09z]

There's no adjustment to do, I open a eBay buyer protection case, seems like the seller is willing to work this out, thanks for all your help, I'll buy some ballscrews from china and see how good they are.