[mickelsen]

I have a desktop CNC router that has been working great, but has started to run rough. I don't know what else to call it. It's started to produce inconsistent results, with non-repeatable errors that make the cuts rough and unacceptable. I've tried everything I know how to do to get it running reliably but to no avail. I've tightened everything, lubricated the slides and lead screws, and calibrated the movement on all three axes. I've replaced the driver board. I'm using Mach3 and I've tried running it both directly through the parallel port and with a SmoothStepper. I've replaced and upgraded the software. Nothing works for very long. It will appear to be working correctly and then start failing again. The only thing I haven't done (that I can think of) is to replace the stepper motors.
Do steppers wear out? I've been running them for several years. Is it possible that old steppers could account for the problems I'm having?
I'm desperate! I'm ready to scream and tear my hair out. Could someone please suggest what might be wrong? I would greatly appreciate the help.
Thanks,
Mark

[High speed tech]

Yes they will,as all motors wear out. My company fixes spindles, ballscrews/lead screws and servo motors.

[DarinSchmidt]

overtime maybe

[ger21]

I'd say that it's very likely that the steppers are NOT the problem. Unless you disassemble them, they should last a very long time.
Does the problem affect all the axis, or just one? If just one, try swapping the motor from a good axis.

[Bob La Londe]

I'd say that it's very likely that the steppers are the problem. Unless you disassemble them, they should last a very long time.
Does the problem affect all the axis, or just one? If just one, try swapping the motor from a good axis.

"IS" or "IS NOT" ?

[ger21]

sorry, are NOT the problem!

[mickelsen]

I have three somewhat larger stepper motors that are essentially brand new, so I swapped them out with the ones I'd been using for a long time. For the short time I've been running them, they seemed to have solved the problem. I'll will continue to watch it closely. In the meantime, a big question has been raised in my mind:

To repair or to replace...that is the question! (With apologies to the Bard.)

I don't even know if there are services that refurbish stepper motors and what such a service would cost. Would be cheaper to just buy new ones?

[Bob La Londe]

Very intersting. How many hours do you think you have on your stepper motors? 1000, 5000, 10000, 20000?

I am having a similar problem on one of my machines. I don't know for sure how many hours I have on it, but probably well over 10000. I don't remember when I put them on. I do have a spare set of the same motors on another machine with much less time on them.

Makes me wonder how much life I took out of the motors while they were just sitting there idling.

[RomanLini]

Failure modes of stepper motors are generally bearing failures.

The magnetics can be degraded if exposed to an alternating field, this only really happens if you try to run a stalled motor, and it takes a long time to degrade the permanent magnet field.

If the screws have become loose and the stators have shifted position (or motor has been disassembled) that can damage the magnetic alignment.

If there is a winding failure the motor generally stops working, although an intermittant winding failure might cause some erratic operation.

Personally I agree with Ger21, it's more likely you have a mechanical fault somewhere or maybe a bad connection in the wires to the stepper motor somewhere. Inside the motor is probably fine.

[stewi]

How warm do your steppers get? Excessive heat will quickly degrade the permanent magnets.
Measure the holding torque from a new motor compared to a worn motor.

[Al_The_Man]

A DC stepper motor is rated for a continuous wattage, which is the Rated voltage x current.
Current rating will be the Rated voltage/winding resistance.
Max.

[mickelsen]

Hi Stewi,
My steppers run hot but I thought that was to be expected. How hot do they have to be in order for it to be "excessive"?
Mark

How warm do your steppers get? Excessive heat will quickly degrade the permanent magnets.
Measure the holding torque from a new motor compared to a worn motor.

[ger21]

Most steppers are rated to run safely at 80°C, or 176°F.

[Al_The_Man]

Hi Stewi,
My steppers run hot but I thought that was to be expected. How hot do they have to be in order for it to be "excessive"?
Mark

More than the rated wattage!:nono:
Al.

[RomanLini]

80'C is very hot! It will cook meat and give you serious burns if you touch it.

55'C is too hot to hold your hand on it continuously, but is fine for a stepper motor. >60'C will start to give burns.

Also modern magnetics use rare-earth magnets that are quite stable and unchanged even when hot. The 80'C max temp is a insulation class spec, it's about the safe temp of the windings and insulation, not the safe temp of the magnets.

[stewi]

Following michelsen's failure description his machine runs fine and after a while motors are loosing steps, leads me to believe, that the motors were overheated and the magnets lost their power.
For the price of the cheap imported steppers, it is hard to believe they are using rare earth magnets.
I have actually never measured the motor temperature and go by the same method RomanLini mentioned. If it is painful to touch, it is too hot.
I rather reduce the input voltage and loose some torque, than a motor.
Michelsen, when you replaced the driver board, did the switch setting for the motor current match the current rating of the motors?

[philbur]

The OP hasn't said whether he has had the steppers apart.:nono: His post indicates that he may not be aware of the problem related to disassembly.

It seems that all three axis are acting up at the same time. It would be an extreme coincidence if it is all three motors faulting at the same time.

If it were only one axis at fault it would have been a better process to have switched motors across axes.

Phil

[mickelsen]

I purchased the steppers from HobbyCNC. I don't believe that they sell cheap imported motors. And I have never disassembled the motors. I've only swapped them back and forth between machines. Unfortunately, the problem is back even with different motors.
In my latest set of tests I've noticed something that might be significant. I'm cutting circular holes in some Poplar. There is a little ridge cut each time the cutting tool goes down a notch, but these ridges only show up in a small portion of the circular cut, maybe 20º-30º. The rest of each cut is pretty smooth. I don't know if these ridges correspond with start of each cut, but I'm wondering if this might have something to do with the plunge cut at the start of each circle. Could this be caused by slow acceleration of the Z-axis? It sort of looks like the circular cut starts before the plunge is done. Nevertheless, I don't quite see how this could cause what I'm seeing, but I don't know what else it could be.
I hope this piece of information will help someone to see what might be wrong. I've been unable to figure it out and I'm getting very frustrated.
PLEASE HELP!
Thanks,
Mark

[stewi]

It sort of looks like the circular cut starts before the plunge is done.

Assuming you didn't program the circular cut as a 3D cut and the z axis suppose to move first before the circular cut, than this is a totally different issue than motor wear.
1. Is the bit capable of plunging or drilling holes?
2. How much backlash you have in the Z-axis?
3. How much play do you have in X and Y?
4. Cutting circles requires the motors going through different velocities while synchronizing the motion. At one point motors could get into resonance and loose steps.

Search this forum about low speed resonance of stepper motors if you find that particular while cutting circles motors are acting up.

[Bob La Londe]

Quite often you get a little nub or sometimes divet where the cutter plunges. If you want a smooth bore you need to run a continuos helical cut.