Overheating stepper advice please

[cncjunky2011]

Hi,

I've just finished assembling the Y axis on my machine and the stepper is overheating after around 20 minutes of use and starts to stall. The coupler is really really hot to touch at this stage too so the heat is being transferred from the stepper shaft to the ball screw (not good).

The motor is a nema 34 and pretty beefy at 118mm in length.

I believe I have found the cause and wondered if anyone else has experienced this. I believe it to be the ballscrew as after close inspection it seems to be warped pretty badly, I'd say without putting the dial indicator on it, it's the best part of 1mm to 1.5mm snake warped and I think over a period of time it's causing the motor to work too hard and causes the overheat.

Just wondering anyone elses thoughts on this please?

Taking the mount ofnthe nut the Z runs smoothly along the Y axis with no resistance so my guess would be the ballscrew warp is the culprit.

Cheers everyone.

[ger21]

and I think over a period of time it's causing the motor to work too hard and causes the overheat.

Just wondering anyone elses thoughts on this please?

Steppers don't work like that. Additional loads won't make them get hotter.

Most likely, you're current or voltage (or both) is set too high.
What kind of drives are you using, what voltage power supply, and what current?

And what is the current rating and inductance of your motors?

[cncjunky2011]

Hi,

Thanks for the reply.

The power supply is a 500W linear (Unregulated) power supply with three main outputs at 68V (6A) and a single auxilary output at 5V (1A)

Driver is set to 6A max, nema 34 6a, 3.6v

I have an identical control box in another machine running smaller nema 34s with the same driver settings and all motors run with no heat whatsoever?

Any thoughts? I'm well confused? I thought it was the screw but not so sure now lol

[johnmac]

Are the drivers set to reduce current for "holding"? Reduced holding current will reduce heat. Steppers can get hot to the touch and not be running too hot. Most have a maximum temperature close to the boiling point of water. (100 Deg. C). Some heat will dissipate through the mount. This is normal, and one way to cool the motors. You could try reducing the current to the motors to say, 5 amps and see if the motors run cooler. Yes, they will have less power, but if they still have enough power, its an option.

John

[cncjunky2011]

Well after playing around it does appear to be the ballscrew. If I rapid at 5000mm / min the motor runs only warm, if I change the rapid up to 8000mm / min the motor overheats after about 20 mins of fairly busy work ( I do sheet work).

The motor is attached to a 20mm aluminium plate and yes the heat should disperse through this but as I first pointed out the warped ballscrew was causing a problem and here it is.

When the screw was turning at 8000mm / min the warp was causing a large amount of energy which wasn't really noticing as the nut was attached and keeping it looking straight. In fact this energy was finding its way to the coupler which in turn was getting absolutely boiling hot. The heat was then transferring to the motor shaft and making the motor overheat.

Changing the ball screw solved the problem immediately.

Now who would have thought that was possible!

Thanks for all the replies anyway, just glad to get it sorted to be honest as problems like that can drive you nuts!!!!

[RomanLini]

Thanks for posting the solution. Too many people ask for help then never post back when it's solved.

I hope your stepper motor shaft is ok, it probably has some level of metal fatigue and may fail in the future if stressed.

[cncjunky2011]

Thanks, I spotted it early and as it's a 8nm nema 34 I think it's beefy enough to cope.

Bent ballscrews, who needs them eh!