Roton Ball nut wobbles on Roton screw

[Smitty505000]

Hey guys,

I am in the process of converting my X2 and have the X and Y done and working great. I am however having problems with the Z. My Z was made from Hoss's site and everything went great until I started to assemble it. I am getting a lot of wobble and have narrowed it down to the Roton ball nut on the screw. It is visibly wobbling on the roton ball screw. It is out about .06 only 4 inches from the nut. Is this normal for these inexensive ball nuts? Or maybe a defect?

Thanks for any help,
Smitty

[LUCKY13]

I am not exactly sure of what your saying the problem is. Is the screw wobbleing out of round?


There are a few things that could cause this, but first is it normal? Even a lower cost screw & nut setup would normally run pretty true. I wouldnt expect perfection but .060 thou is a bit much.


But first you need to figure out what & why is out of specs. I would remove the screw & take the nut off. If you have not ever done so then you need to research & learn how to do this without causing damage.


Then take the screw & check to see if its bent, plus measure the depth of the threads to see if they are right ( different places & all around to know if they where cut on center). Then the machined ends need to be check to see if they where cut on center. Even if the screw is OK if the machining of the ends was done off center then it could cause movement of the screw when its mounted & rotating.


Its doutefull the ballnut itself would be causing such a problem with it being mounted stationary. But yuo should be able to feel such a thing when you remove the assembly by rotating the nut. I would expect the ballnut nut to move smoothly unless it has some kinda odd problem.

There is a good chance you may need to replace the screw, but first you need to know whats wrong. It is possibly to straighten a bent screw if you do it right. BUt if the ends where machined with the screw bent then its probably not going to help. One good thing is the screw stock is fairly cheap compaired to the maching & ballnuts so maybe its a cheap fix if you can pinpoint the problem.

Jess

[TXFred]

Yup, that's an issue with the Roton nuts and Hoss's design. Roton didn't anticipate that the nut would rotate while the screw was stationary. So the external and internal threads of the Roton nut aren't always concentric.

You can try different nuts and see if you can find a good one. Or you could modify the Z pulley to include an adjustable eccentric to bring things back onto center. Or do what I did and live with it. On my mill, the ballscrew had enough flex that the system still worked OK.

Frederic