Ball screw appears to be binding, but is it ...?

Hi,

I'm having real difficulty identifying an issue with my X axis linear motion.

Af first glance, it would appear to be a mechanical issue; however, I've run out of things to test. The fault occurs at a similar place on the ball screw every time, between the blue marks shown on the gantry in the video.

Take a look at this video and see what you think.

https://youtu.be/3D3ZwPQShzo

The machine has run fine for the last 3 years. I've tried removing the stepper motor, and it operates fine, not under load, independent of the other mechanical items. With the stepper motor removed, I've tried pushing the X axis gantry back and forth, and it runs absolutely fine. No binding. Then I thought it had something to do with the feedback from the stepper motor? But clutching at straws.

This issue has got me stumped, so any suggestions would be greatly appreciated.

Thanks,
Oliver

Have you given the screw a very good inspection for any damage in that area?
It could be something like a bit of dirt in the ballnut, but I'd expect that to cause jamming at more than one position.
Have you tried giving the ballnut a good grease, then running it back and forth fairly slowly to work the excess grease out, and seeing if any dirt comes out with the grease?

Are they closed loop steppers?
It could be something like a broken wire, that only looses contact when the cable is flexed in a certain position, but I'd expect that to get worse over time, and to trigger a fault in the driver.
Might be worth removing the wiring from the cable chain, and if there's no obvious issue with the wiring, running the axis with the cable just held to so it's flexing in a different way.

Failing that, you're probably looking at a full strip down of the nut, to ensure that there is no bits of dirt/swarf in it, but that can be quite an involved job, especially if it uses alternate sized balls, and as your screws are multi-lead, there's going to be a few bearing tracts to clean/reload!

Thanks for your advice. I tried clearing out and lubricating the ball nut. This appeared to clear the fault and worked fine for a couple of days.

The stepper is a closed loop stepper. I decided to swop it out and in doing so found a broken cable.

It was obvious after I found the fault. As the cable chain curled over it caused the fault to occur, this resulted in the issue happening at the same place every time.

Lesson learned, anyway after all that oiling and greasing it's running like a dream.

Thanks.

Oliver,

Cable faults like that can be so easy to miss until you're right on top of them, and even then they can feel like the last thing you'd suspect...especially when everything else checks out mechanically. The fact it was repeatable at the same screw position is what threw me, I was thinking the ballnut!

Glad to hear it’s running sweet again though and I bet all that fresh grease didn’t hurt either :toot:

Nice to get a win on one of these annoying gremlins for once, thanks for confirming, it’s these little nuggets that really help others down the line when they hit the same sort of brick wall.

:eagerness: