AO-100 X-end-motor catching on the leadscrew

This is a follow up on this topic:

I’m having a new problem tonight with the left side of the X axis not moving as it should. If I send a move command of the Z axis in Pronterface, the motor end of the X axis will sometimes jam, even if the Z motor and the leadscrew turn as they should.

The result is quickly something like this:

I then have to disable the motors, and turn one of the leadscrews by hand to level the x axis. I then try to move the z axis again, and it will be fine for 10mm of travel, and on the next 10 the left side will jam again. Or after 10mm of travel, the left side might have traveled 7 or 8mm, or not at all.

Some things I’ve done before and after noticing this problem:

  • Tightening a screw on the upper pillow block bushing after I found it was at least 1/32" loose.
  • Tightening the 4 screws that hold the x-end-motor and the x-clamp because the rear x axis smooth rod appeared not perfectly sandwiched. Thinking I had overtightened them and that was the source of this new problem, I loosened them again, with no change.
  • I added a little general purpose grease on the leadscrews to try helping the brass nuts, no change.
  • I noticed the right lower Z motor mount was not centered. If was off by 1/4" toward the front of the frame, which would make the whole X assembly crooked (not square). So I centered it.

From what I can see, the brass nut is very tight in the plastic and the leadscrew does not move freely. I shot a video to explain it (please be lenient with my accent):

I’m hoping you guys have ideas. I’m not a tinkerer/troubleshooter, and I’m really getting depressed with this.

Update: I decided to disassemble the x-end-motor to see what was happening with the captive nut. I removed the x-endstop bracket, the z endstop switch, then the motor, then the lower pillow block bushing, and finally the 4 screws holding the x clamp to the x-end-motor bracket. Everything looked like it should…

That’s when I noticed that the left leadscrew was quite higher than the right one. It was overshooting the top of the upper Z mount by at least 6mm if not 10mm… I looked at the ACME clamp (Z axis coupler)… The lead screw was almost out of it! Also, the clamp is split right at the upper screw hole.

I wish I had found that before I disassembled the x motor bracket assembly! :angry:

It’s too late to continue, I’ll put everything back together tomorrow, I hope that’s the source of the problem… And then I hope I can use the broken coupler until I can print a replacement.

Yeah, if the X carriage assembly isn’t level, the acme nuts on one side (usually the lower side) lower side can bind and cause enough friction that the motor can’t turn. The problem is the nut itself ends up at an angle, putting pressure on the inner and outer threads. I ran into that a few times when I was taking things apart and reassembling during testing for the AO-Taz x ends. Ironically the dual nuts in that particular upgrade eliminates that as an issue for the most part. To fix it, with the machine off, just use your fingers to manually turn one of the z axis rods until everything is level. I find a quick way to level that axis is to home the machine, use a business card to set the distance between the nozzle end and the bed (with the nozzile heated for at least 5 minutes to print temperature to account for expansion) then move the nozzle all the way to the end of the xx axis and repeat, and then a third time at full X and Y. The Stepper motor doesn’t care where it starts, it picks whatever position it powers up in as its beginning point.

That’s what I had been doing, as I mentioned already:

Yesterday I did this more times than I can count.

Tonight I assembled everything back together and the left leadscrew is now fully seated in the Z coupling. In Printrun I clicked on the Z+10 button a few times, then Z-10, home and repeat. Travel seems to be doing OK, although I sometimes hear a brief sound like there is some resistance to the movement.

I also noticed that the z coupling is not only split at the upper hole, it also seems to be delaminated at the middle. It’s got no more rigidity anymore. First thing to print is a replacement, but which one? I don’t want to use the stock one, I feel that printing it bottom up makes it too fragile. Maybe I can adapt the one 1013 did (in 2 plates) for his TAZ…

There is a replacement z-coupler here: or here: that is much more rigid in design

Thanks, I see there is a small difference with the AO-100 couplers, I’ll print them out.

I printed two tonight. Do I have to cut the middle slots open?

The bottom layers are UGLY. There was too much heat, they got squished pretty bad (the part lost more than 1mm in height). I started over the print, reduced the bed temp to 90º from 110, no change. I let it go and after 5-6 layers, things were back to normal. Could a 60W incandescent light bulb about 6 inches from the bed have prevented heat from dissipating on the first layers?

I don’t have a fan to cool the parts. It’s one of the upgrades I plan to do…

BTW I don’t see much difference between these “beefy” couplers and the ones on my AO-100, apart from the flat on the hole for the motor.

Good thing I printed two couplers, because the right one was broken too!

The AO-101 coupler are indeed “beefier” than my AO-100’s.

Had no answer on that, I found pictures here that show the slots are not cut open.

We saw that happen in the bot farm relatively frequently(24/5 printing pushes the machines pretty hard) and swapped every machine to the new couplers.

No need to cut the slots open, it is part of what makes the parts stronger