Stepper motor problem

[fizzy]

I have now fixed my ballscrew that lost it's balls.
But now I am having a problem with the stepper motor. At high speeds it is stalling. It feels really stiff to turn by hand - the other one is fine.
Could it be a bearing? Are they easy to take apart? Watched some Youtube videos and there doesn't seem much to them.
Any advice welcome before I wreck it.

 

[tigdlo]

If its a nema 17, 23, type jobbie with no encoder and not working anyway you have little to lose. I would take one cap off at a time and not remove the rotor or allow it to move in or out of the housing as this would give it the best chance of not losing any magnetism, if that is even possible..... While removing the cap you can pull or push on the end of the shaft to keep it well seated on the opposite cap.

 

[knighty]

when it's stiff to turn by hand, is it stiff in a smooth way or can you feel the steps?

 

[Agroshield]

I am guessing the stiffness is with it disconnected from everything else?

Turn it slowly with a clock on the end just to confirm nothing is bent or eccentric.

Swap the two motors and see if anything changes. That will eliminate or confirm any influence of the driver or the step frequency.

Edit:

Another non-disassembly suggestion: put a multimeter on every set of windings, both good and bad motor. Any variation in the readings might tell you something.

 

[fizzy]

It is very stiff when disconnected. You can still feel the steps but it is far stiffer than the other one.

 

[m_c]

Given it's age, you've not really got any nothing to lose, but personally if the mill is still useable, use it as to machine some decent mounts for some Nema 23/24 motors, and get rid of those cobbled together standoffs.

Something like this - https://www.cnc4you.co.uk/Stepper-Motor/Nema23-2.2Nm
Getting the mount will also give a far better setup than those cobbled together standoffs it has, and you'd also need a suitably sized new coupler - https://www.cnc4you.co.uk/Coupling/Lovejoy-Oldham

Although, is the existing setup using a proper thrust bearing setup for the ballscrew, or is it relying on solid couplers and the stepper motor bearings to control endfloat?

 

[fizzy]

Given it's age, you've not really got any nothing to lose, but personally if the mill is still useable, use it as to machine some decent mounts for some Nema 23/24 motors, and get rid of those cobbled together standoffs.

Something like this - https://www.cnc4you.co.uk/Stepper-Motor/Nema23-2.2Nm
Getting the mount will also give a far better setup than those cobbled together standoffs it has, and you'd also need a suitably sized new coupler - https://www.cnc4you.co.uk/Coupling/Lovejoy-Oldham

Although, is the existing setup using a proper thrust bearing setup for the ballscrew, or is it relying on solid couplers and the stepper motor bearings to control endfloat?

In fairness the other axis works very well.
It may have been me that ******** the Y axis. Wound it out too far - then winding back in it stalled. I had to rebuild the ball screw which is now fine. But the motor is really stiff. Of course it may have been like that before but it is definitely not right.
The couplings he has used have a floating plastic spacer so aren't too bad.
The ball screws are actually very expensive ones.
There is a proper thrust bearing in place.
I will try to fix the motor but if not I will just buy a newer replacement. Mach3 allows you to fine tune each axis so hopefully it won't be a problem using to different motors.

 

[m_c]

What makes you think the ballscrews are "very expensive" ones?

Very expensive would be something like C3, which at that size of machine, would probably cost more than the entire value of the machine.
Now given the standard of the rest of the 'conversion', I'd very much doubt that they spent that much money on the the ballscrews.

 

[fizzy]

What makes you think the ballscrews are "very expensive" ones?

Very expensive would be something like C3, which at that size of machine, would probably cost more than the entire value of the machine.
Now given the standard of the rest of the 'conversion', I'd very much doubt that they spent that much money on the the ballscrews.

They are Steinmeyer - can't remember the model number but I looked them up and they were £250 each. Hence being determined to fix it.

 

[julianf]

CNC can be so full of gremlins - i would suggest, if you can, swapping the entire upstream for that stepper to one of your others (assuming the other is "known good") and swapping the bad one's upstream to the other stepper.

If your driver is doing odd things it will show up in the motor, etc.


I guess i built my machine over 15 years back. ALL of the electronics, except for the actual motors, has been changed more than once. The motors seem the most indestructible part of the whole setup.

That doesnt mean to say yours are not stuffed. But id suggest a check would be worth the time it takes?

 

[fizzy]

I have taken the stepper apart. Bearings seem fine. I have discovered though that you can "adjust" the way the shaft turns by tightening and loosening the end caps. It must be built to crazy tolerances. By fiddling around I have managed to get it running smoother but there is still a tight spot. I suspect perhaps a slight bend in the shaft or maybe some play in the bearings. Probably easiest to just buy a new one

 

[fizzy]

Well it is fixed - for now.
The solution. Leave one screw slack
The top end plate is at 90 degrees to where it was before as well.
Has ro be a slight bend in the shaft or the case has distorted slightly.