Stepper motor bearing failure?

Has anyone run across the stepper motors on the K40 getting worn to the point they chatter?

You’ve all probably seen a toy car or cheap DC motor wear to the point that when the motor tries to go fast it slows considerably and chatters as it wobbles in the bushing and how a tiny drop of oil will get it working for a short period. That’s the effect I’m seeing and hearing.

I even removed the X axis bearing, OMG they bolt mirror #2 right to the motor, and ran it out of the machine in raster mode at 200 and 300mm/s over 200mm distance and it noticeably chatters even without side loads like when installed and belts are tightened.

I didn’t think bearings did this but since I popped the back off of the motor, I can feel and see slight movement when twisted 90 deg to the axis of rotation.

I also recall that these are not GT2 belts and so bizarre you don’t find grub-screw based gear drives and these puppies are heat pressed onto the shaft. Replacing motors, pulleys, belts and idlers the only option?

The belts are standard imperial MXL 0.08 inch belts (in metric, 2.032mm) in order to support motion in exactly 1/1000 inch increments. I see some MXL pulleys with grub screws; not sure if they have the right tooth count though.


Thanks! I counted 20 teeth on the X axis.

MXL-20T is the base search then. Depending on the shaft size:

(Also, I updated the links for replacement belt and added previously-missing width specs.)


Thanks Michael, I wasn’t getting good hits with “MXL .08 pulley gear”. looks like a smallish motor and maybe than 1 or 1.2A rating. Y axis is double shaft so that one might be a tricky replacement. With a new motor, I don’t really have to stick with the 5mm shaft OD so will depend on what motors I find.

Sad thing is, I have a box of 5-6 motors from when I was making Mini Kossel delta 3D printers but darned if I can find them. Found my hotends, bearings and other parts but not the motors and still I would want to get a new Y axis motor anyways so might as well get a match. Need to pull it to see what it’s sizing is and probably need same size to fit the shaft extender coupler.

You need need 400 step (0.9°) motors anyway, and the vast majority of motors used in 3d printing are 200 step (1.9°). blue-box-guide [Smoothieware] has sample motor specs for at least one K40.

Bearings tend to be standard. Thought about just replacing the bearing in the existing motor?

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0.9deg motors would provide more resolution for sure. I’ve not researched if that’s a good upgrade or not since there’s other slop in the system as it is and that might lower the max speed. Can smoothie still do 300mm/s with 16 microsteps and 0.9deg motors?

As for the bearings, I was looking at it and figured it was pressed on and pulling them might be a bugger. Have you pulled and replaced bearings on these as I’m not opposed to giving that a try.

0.9° isn’t an upgrade. It’s stock. If you replace with 1.8° you get lower resolution.

I have pulled and pressed bearings in a much larger motor (3.25HP 90V DC). I have a bad stepper that I haven’t pulled apart to try only because I have extras floating around…


I would have not guessed that and didn’t bother to look at the numbers in the config when the motion moves were on target I just never looked into it. Thx for the heads up.

I found Don’s Things blog post on the K40 motors he ran across and sure enough, 0.9 deg 0.48A NEMA17 on X and 1.0A on Y.


Just watched a video on replacing the bearings and in the video they just slipped off the motor shaft!
I had to try so I opened it up again and could not pull the bearing off the shaft with my fingers like in the video. i could probably press a new one back on just using my vise but getting it off without a small puller is no-go. Step motor repair (bearing replace) - YouTube

I might just hack a mini puller together by welding 3 small screws onto a washer then weld a nut to the washer. I need to find a link on the trick to pulling the belt drive gear without damaging anything and if that comes off then I’ll order the bearings.

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I just watched a few videos on pulling these pressed on gear drives and I should be able to do this without damaging the motor so I ordered the bearings today. 10 625zz bearings for $8 but won’t get them until Sunday.

Thanks for pressing me forward with this @mcdanlj because now there’s no reason for stepper motors to be thrown away unless physically burned or something.


Update, I might get the bearings today! So I had the motor in the freezer all night and I took a small section of angle iron and cut a 5.xmm notch in it using a small drill and hacksaw. A small amount of heat on the brass pulley and a punch took the pulley off handily. The bearing on the pulley side was finger tight and pulled right off. I then took a flat piece of metal from the scrap welding pile and cut a larger diameter slot since there’s a plastic spacer behind the stuck bearing. no heat but a small tap with a punch and the other bearing was off.

The motor is now ready for rebuilding once the bearings arrive.


new bearings fit on without force and with the motor in the freezer for maybe 1 hour, I heated the belt drive with a propane torch for just a few seconds and surprisingly it literally slipped onto the shaft with no friction and immediately on contact with the cold metal locked into place. Super easy rebuild and it’s back in the machine and operational.


I’m so glad that I encouraged you to do this, because this evening I checked the print I started this morning and saw this on my corexy:

That long diagonal isn’t supposed to be there. My left rear motor seized partway through the print.

I pulled the stepper apart and found that one of the bearings was running a little rough and the other… well, the other had most of the bearing material in bits suspended in the space between the rotor and the bearing, but turned only with great difficulty.

I’d had a few failed parts with skipped steps inconsistently before this print, and now I know why!

I didn’t find any loose 625ZZ bearings around the house so I just dropped in another rotor assembly after diligent cleaning, but then I realized that I could have robbed my stash of loose openbuilds wheels, each of which has two 625 bearings. I now have an order for 625ZZ bearings coming in any case! Can never have enough common sizes of bearings, right? :relaxed:


Very good! And I’m quite thankful you even mentioned it or I would have not looked into it and found how valuable and relatively easy it was. Even on the K40 with the pressed on belt gear. Love learning new skills and will never throw away a stepper motor ever again.

I never thought about checking my extra set of Creality wheels. But I have 8 new ones as spares because as you said, you can’t have too many bearings sizes.


I glanced at the openbuilds wheel I have, and they have 625RS not ZZ, and probably want ZZ not RS inside a motor anyway. The ABEC-5 bearings I bought are nice and with the repair done I have a spare stepper motor, it looks like. :relaxed: