Looking for some advice on an intermittent x axis fault

[JohnHaine]

.....The few times I've been there to actually see it happen, the motor makes a high pitch noise then carries on.

....
Sam

Hello Sam, how annoying this sort of thing can be! My mill X power feed is done with a stepper motor and I get the high pitched squeal when and if it stalls. There is a tight spot in the table towards one end and if I try to drive the table too fast that will cause this. It sounds as though you have tried different feeds so may not be that.

One other thing that can happen is that a stepper can have a fragment of swarf in it which gets caught in the "teeth" and jams it. This may go away but then come back in a different place as the bit gets "circulated". I've had this once on a new NEMA 8 motor from a far east supplier. Take the stepper off and disconnect the wires, then try spinning it with your fingers. You may need to try for quite a while but if you suddenly feel the motor jam you've found it. There's no cure really, better to scrap the motor and replace.

[Norvic]

Hello Sam, how annoying this sort of thing can be! My mill X power feed is done with a stepper motor and I get the high pitched squeal when and if it stalls. There is a tight spot in the table towards one end and if I try to drive the table too fast that will cause this. It sounds as though you have tried different feeds so may not be that.

One other thing that can happen is that a stepper can have a fragment of swarf in it which gets caught in the "teeth" and jams it. This may go away but then come back in a different place as the bit gets "circulated". I've had this once on a new NEMA 8 motor from a far east supplier. Take the stepper off and disconnect the wires, then try spinning it with your fingers. You may need to try for quite a while but if you suddenly feel the motor jam you've found it. There's no cure really, better to scrap the motor and replace.

Hi John, yeah it is a little frustrating. Thanks for your suggestions. I've tried swapping the stepper with one on the y axis already which didn't work so I think I can rule out the motor itself. I can turn the ball screw all the way fairly easily and I can't see any damage to the screw but considering how random it is maybe something worked its way into the ball nut which is causing it to stall. I also noticed this morning I can hear the ball bearings circulating which I can't on the other axis so it might be the next thing to investigate.

[ZASto]

Hi John, yeah it is a little frustrating. Thanks for your suggestions. I've tried swapping the stepper with one on the y axis already which didn't work so I think I can rule out the motor itself. I can turn the ball screw all the way fairly easily and I can't see any damage to the screw but considering how random it is maybe something worked its way into the ball nut which is causing it to stall. I also noticed this morning I can hear the ball bearings circulating which I can't on the other axis so it might be the next thing to investigate.

It seems that your ball nut is dry. Try to lubricate it.

[Norvic]

I tried lubricating it directly and a new ballnut and I'm still getting position loss. Although the new ballnut sounds completely normal so it seems unlikely to be a mechanical issue unless I'm missing something else.