[MJRx]

Hi everyone,

I'm currently fine-tuning a CNC machine that suffered a crash last year due to a defective encoder (which has since been replaced). The Y-axis now shows about 0.022mm backlash, and when I test it with a dial indicator, the needle doesn't move smoothly—it jumps slightly even when moving in a single direction.

As part of the recovery process, I already replaced the thrust bearings (same brand as original), and the encoder is new. I also replaced the amplifier itself due to a non-recoverable error indicated on the 7segment indicator.
The X-axis behaves perfectly—no measurable backlash, and the dial indicator tracks smoothly, using the factory backlash compensation settings.
Now I suspect potential damage to the ballscrew or nut from the previous crash. My plan is:

Try replacing the balls in the nut.
If that doesn't help, replace the nut.
As a last resort, replace the entire ballscrew assembly.

Before I go down this path, has anyone experienced similar behavior—especially the jumping dial needle? Could this be a sign of localized damage on the screw or internal scoring in the nut?
Would appreciate any advice or experiences from others who’ve dealt with this kind of issue.

Thanks!

A videoclip about the problem (since uploading that file is not allowed here):
I'm stepping 1 micrometer, and it's somewhat jumping like 10 microns:
https://streamable.com/lqoqni

[MrMetric]

Have you checked the lubrication of the ways to be sure you are not getting "sticktion"?

[MJRx]

the lubrication is okay I just checked that before, the ballscrew is oiled within that area too.

I checked the encodervalues in the system today and that was also correct, each micrometer jumped 10 steps (when I switched on emergency stop I was able to move the ballscrew freely).

For the next step I would try to remove the entire ballscrew and put some new balls into it.

[samlevy0515]

Given the symptoms, I'd opt for a complete nut replacement.

[MJRx]

Does anyone know how I can remove those black shaft couplings?

The motor and ballscrew are already loose but I cannot get it off.

When turning the nut it doesn't seem to be smooth either, especially when I rotate it slowly. Maybe there is some debris inside or some balls are dead or the nut is damaged I don't know. I'd like to remove it and carry it to a company which can restore it. The entire assembly is pretty easy (except that coupling which challenges me at the moment)

[MJRx]

Ok any suggestion what to do next?

Should I better leave it as it is now and forward it to a company to rebuild the ballscrew or is there anything left that I can do?
Both parts are from HIWIN ... dated 2001 quite an old-timer.