Help please - Strange and sudden axis fault on Kossel XL

[rjenkinsgb]

Hi,
My Kossel XL has been working fine for the last couple of years.
(Duet 3 MB6HC; firmware 3.4.0).

I've not used it for a couple of months (too busy with work).

I just tried to print something and found that one axis is moving around 10% further than the other two - when it went to probe the bed centre, it was a long way off to the side.

Homing then jogging Z- shows the same effect - the front left axis (as I have it positioned) moves proportionally too far as it travels down, and the same jogging back up - so all three level gradually level out again as it gets back to the top!

I've checked the config file is not corrupt; all three axis parameters are identical.
Also tried power off and let it restart without attempting to print, no difference.

The motor pulleys and belts are all fine, no slipping.

Any ideas?

Thanks,
Robert.

[dc42]

@rjenkinsgb are you by any chance using steel-cored belts?

[rjenkinsgb]

@dc42 No, just generic fibre reinforced ones.

[dc42]

@rjenkinsgb the reason I asked is that users have experienced similar symptoms when using steel-cored belts, because the belts are not meant to run over such small pulleys and the cores break. I am wondering whether something similar may have happened to the belt on that motor. Also check that the pulley grub screw is still tight.

[rjenkinsgb]

@dc42 Problem solved, thank you!

I'd already checked for any slip or backlash by holding the belt while jogging small amounts, but was going to double-check the grub screws to be certain.
They need a torch to see them clearly.

They are OK - but I was not expecting the pulley to have changed size!
A small fragment of fibre reinforced tape from somewhere was stuck on it, so the belt was moving slightly further for each motor rotation.