[davidcsm3d]

I have a mini mill (like a Precision Matthew’s) I have converted to cnc with ball screws and stepper motors.
When I run the x axis, there is an intermittent ‘thunk’ sound probably every 40mm or so. It sounds like it’s either at the end of the ball screw near the connector or even in the stepper motor itself. The x axis runs cleanly with no sound as it moves in x+ (to the right), but when I move it in x - (to the left) it gives a thunk sound every 30-40mm. I have adjusted the gibbs and loosened them tightened all the bolts. It only happens in one direction, which seems odd. It’s possible the stepper motor is not 100% in line with the ball screw and I will check this tonight. So I am trying to understand why the thunk sound only happens in 1 direction and what else to check. The parts are brand new and oiled.

[awerby]

I doubt it's the motor itself. But check the couplers that attach the motor to the screws; if they're working loose, like from a set-screw that's lost its set, then they can flop around on the shaft and make noises like that. Do it soon, before it galls the shaft end and becomes extremely difficult to remove at all.

[davidcsm3d]

I doubt it's the motor itself. But check the couplers that attach the motor to the screws; if they're working loose, like from a set-screw that's lost its set, then they can flop around on the shaft and make noises like that. Do it soon, before it galls the shaft end and becomes extremely difficult to remove at all.

I have rigid couplings at the moment. I will replace them tomorrow with more flexible couplings in case the shaft is misaligned. Whilst the couplings are off, I will see what happens if I run a tool path with the motor not attached at all to the x axis. I did more tinkering last night and the noise only comes from running in one direction. Thanks all

[davidcsm3d]

I took the x axis apart. The nut on the end of the thrust bearing appears to be loose, I can wind it up and down the end of the ball screw by around 5mm by hand.

[davidcsm3d]

I think I have solved it. After almost taking the whole thing apart and swapping stepper motors with no success, I just rewired the internals of the controller box with screened cable. It’s behaving better now. I have learnt so much fixing this one issue.

[awerby]

I'd still suggest swapping out those rigid couplers for flexible ones, preferably Oldham-type couplers with a rubber "spider", which last longer than the one-piece helical-slotted type. Slight misalignment can snap off your motor shaft after a while.