Nema 34 motor stalling Randomly

First let me say thank you to anyone who is taking the time to read and respond. I have a home built CNC router constructed of extruded aluminum. All 3 axis ride on Linear rails and are driven by NEMA 34 motors and 1605 ballscrew. I am running Mach4 on a WIn 10 PC connected to a Pokeys57CNC through ethernet, which drives 4 DM860A drivers powered by 4 different 8 amp Power Supplies which out put 60V. After I had finally got everything working smoothly I was able to run the CNC for about 16 hours over the course of a day and a half which I did a Large 3D carving of a T-Rex Skull, and small inlay and I large piece of etched glass just so I could put it through it paces. It gave me no trouble. However I did notice some wobble in my ballscrews which turned out to be the shaft couplers so those got replaced on the next weekend and I then went to face cut some rough lumber and began having an issue with the X axis motor stalling randomly. I changed the motor out for another NEMA 34 and the problem persisted. I then had the X axis just rapid back and fourth which I monitored the voltage until the motor stalled and saw a consistent 60volts the whole time. I then repeated this while monitoring current and the power supply never output more than 1.2 amps. The driver has a peak of 7 amps. Just for giggles I also adjusted the driver from using 1/16 to 1/8 with no change. I then moved to the Z axis to had the rapid up and down to see if it would stall and it took longer to happen but it eventually stalled as well. At this point I'm thinking its the Pokeys57CNC board since of the 2 axis I checked they both had the issue. The only other thing to happen to the CNC before the issue was that I installed some software to be able to pull files from a network drive. However, I pulled the PC off the network and ensured nothing was running in the background but still had the stalling problem. I would appreciate hearing if anyone had any other suggestion on what I might try before I buy a new Pokeys57CNC and swap it out.

Have you tried switching the motor leads from X to Y and seeing if the fault follows along? That might give you a clue as to what's going on. Be sure to power everything down first, and let the capacitors drain before disconnecting any motor wires.

If the steppers are getting really hot I’d find a way to make them cooler and retest.


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awerby thank you for responding. I had considered swapping the driver and power supply on the X with the Z axis but before I tried that I just ran the Z axis by making it rapid up and down and was able to get it to stall as well. It took about 12 minutes where the X axis stalls in about 6 mins. The x axis motor gets close to 100 F and Z axis motor was about 75F. Not sure it matters though. So of the 2 axis I have checked both end up stalling. I have not tried to make the Y axis stall since it uses two motors and I don't want to rack the gantry if I can help it. Since both the X and Z axis motors will stall the one common item between both is the Pokeys57CNC which is why I am leaning in that direction.

What speed are you trying to rapid at?.

I had 1080oz, nema34's / 60V on my mill, I couldn't rapid above 2000mm/min at 7A on driver.
I swapped motors to 566oz, nema 24's and dropped to 4.2A (kept everything else the same).

It doubled my speed with no skips!!.

My theory is, the nema 34's are too much. A motor needs to drive a load with a bit of resistance against it so it uses it's torque.
If it is effectively running 'free' it will skip around and/or overshoot.

My Z axis still has a nema34 on it but I'm going to bump the voltage up to 80V with a bigger driver.

That's an interesting thought that I hadn't considered. I'm suing 4 960 in-Oz motors I purchased from Avid CNC. The X axis rapids at 120 inches per minute (3000mm / min) and my acceleration is set to 10. The Z axis runs a bit slower at 80 inches /min. The initial stalling though was occurring during a cut while feeding at 70 inches per min as well as several times there after, always in different places and at different times. The only variable that seems to impact it is time. When starting from cold the machine will run for about 6 minutes before having an issue but the longer it runs the more frequent the stalls. The motors are warm but not excessively so. The cabinet with the electronics also stays nice and cool.

Hi Michaeil,
1) There is no such thing as a "random" event with a machine
2) There are 2 common ways to stall a motor and they are actually the same thing a) apply a load that exceeds the torque the motor can provide b) try to accelerate it faster then the motor can respond to which is just the same thing as a)

Since the motors are not getting excessively hot and assuming the electronics are doing what they should be doing since they are doing the right thing initially, and you say it occurs as the machine warms up.

1) check that the ballscrews are correctly lubricated and the nut is not tight. As the nut warms up it can expand and create lots of load. Include the support bearings in this investigation and that the driveline is aligned. sawdust and stuff can get into drive nuts and cause jamming issues
2) as the stall occurs during rapids tune down the acceleration and see what happens or run the test slowly so accel is not a factor, you say the accel is 10? 10 what? cheers Peter

First let me say thank you to everyone who responded. I think I have it figured out. I had only done two things to the CNC between the time it was running nicely and when I started having stalls. One was to replace the shaft couplers and the other was to install software so i could access a network drive and it appears to have been the later. After uninstalling the software and rebooting I was able to successfully run the X axis back and forth on rapid for 30 minutes with out issue and with no other parameters changed. Considering it would only run for 5 to 6 minutes before I feel like that was a pretty good indicator. i will have to reinstall the software and see if I can recreate the stall to be certain but at the moment that appears to be the issue. Since I was using an ethernet to talk to the Pokey57CNC I can only guess that the software for the network drive was occasionally interfering, but that is just speculation. Thanks again to those that helped.