RE: Skewed XY-Plane (Z Rods, Heatbed)
They should have at least 2 part numbers because the cable length is different. I ordered the ones with the long cable and the pitch is correct.
[...]
In the next days I will check the C1 of a colleague. It was one of the first batch and I am quite curious...
Yes, of course the motors configurations with different cable lengths have different part numbers. I was referring to a differentiation by lead screw pitch.
If your colleague's Core One was factory-built, I think it is less likely to have this issue. My theory is that the problem arises (mainly?) with kit builds, because the kits contain motors from two different batches: Four in the pre-packed motor set (which has the motors that also go into an MK4s), and then one lead-screw motor is added separately and presumably comes from a different shelf, picked at a different time.
RE: Skewed XY-Plane (Z Rods, Heatbed)
It was also a kit. I never get built printers from Prusa, I like the building experience 😉
RE: Skewed XY-Plane (Z Rods, Heatbed)
It was also a kit. I never get built printers from Prusa, I like the building experience 😉
I was referring to your colleague's Core One, which you said you planned to look at next.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Well, I have a kit and it has the left screw pitch off. And I also have a prebuilt one and it has the rear screw pitch off. So it's not just the kits that suffer from the screw plague. Also it's not like these are 4 short ones and 2 long ones. Instead it's: 2 shortest, 3 +- equals, and 1 the tallest. Something like -0.25mm, 0, and +0.5mm. Unfortunately I don't have sufficiently precise tools to measure in absolute lengths. But the bad news it's NOT just TWO batches of screws.
RE: Skewed XY-Plane (Z Rods, Heatbed)
It was also a kit.
And yes, I checked it today. Same issue. The front left motor (same as with my months older Core1). Swapped the motor with a good one. At least the trapezoid nuts did not bind, they ran freely.
I also adjusted the belt tension with the new resonance method, which is extremely useful. That is a very good feature.
Next week I will deal with support when I'm back in the office.
RE: Skewed XY-Plane (Z Rods, Heatbed)
For a simple sanity check, try the test that @petulf suggested. It won't be affected by other causes of skew.
RE: Skewed XY-Plane (Z Rods, Heatbed)
For a simple sanity check, try the test that @petulf suggested. It won't be affected by other causes of skew.
Yes, that's the most direct test -- a distortion-free measurement of each screw's pitch, without the need to remove the screws from the printer (yet) and without the risk of mis-counting threads.
Just don't expect Prusa support to buy into this measurement. At least when I spoke with them a few months ago, they were apparently not aware of this forum thread, and certainly not of this measuring method.
RE: Skewed XY-Plane (Z Rods, Heatbed)
I printed a measuring tool. A U-shaped part, 224mm long and every 20mm a small nub. It fits on the rod and shows if there is a problem or not. I can post it if you like.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Well, I have a kit and it has the left screw pitch off. And I also have a prebuilt one and it has the rear screw pitch off. So it's not just the kits that suffer from the screw plague. Also it's not like these are 4 short ones and 2 long ones. Instead it's: 2 shortest, 3 +- equals, and 1 the tallest. Something like -0.25mm, 0, and +0.5mm. Unfortunately I don't have sufficiently precise tools to measure in absolute lengths. But the bad news it's NOT just TWO batches of screws.
I remember discussing this with @jürgen a few weeks back in another thread. Back then Prusa support, if I remember correctly, even gave the tolerances they would expect from the motors, and they all will fit the tolerance, as such there is no bad batch. The problem is that different production runs (or even multiple suppliers) of the motors got different deviations from the tolerance and when you get parts from batches with large deviations you get the skew. Upgrade kits are probably more impacted as the new motor is nearly sure from a different batch than the mk4s motors, again if the deviations are compatible you won't notice much, if they diverge ... skew.
Aside from Prusa adding more checks when building a kit nothing we can do but ask for a replacement.
Probably another reason for Prusa to move away from the kits (buikding in house and testing for skew may be more efficient than checking all rods beforehand).
RE: Skewed XY-Plane (Z Rods, Heatbed)
Please post your tool. Great idea!
RE: Skewed XY-Plane (Z Rods, Heatbed)
Just to add another datapoint to the collection, I put a Starrett #98 level on the bed, leveled it with a few sheets of paper on one end (my bench isn't perfectly level) and ran it top to bottom. I did this left-right and front-back. The difference over travel, left to right, was 2 divisions, which is 0.010"/foot or about 170 arcseconds. Front to back it was half that. My Core One is a kit purchased during the Black Friday sale.
I'm not sure it's reasonable to expect better than that from rolled leadscrews. Ground, sure, but the price of ground screws is probably an order of magnitude more. It shouldn't have any effect on prints because the error would be distributed over a huge number of layers. It seems to be linear. The only effect would be the top to bottom parallelism of a tall print, an issue one would have to deal with even with an injection molded part.
RE: Skewed XY-Plane (Z Rods, Heatbed)
As requested, I uploaded the tool on Printables:
https://www.printables.com/model/1543676-tool-to-check-the-pitch-of-the-z-axis-spindles-of
RE: Skewed XY-Plane (Z Rods, Heatbed)
I carefully measured my z axis rods. I get 100 threads in 200 mm exactly on all of them. I used a paper tracing then counted them in 10's and measured as many threads as I could at once to remove some of the error. (got a bit over 110 good thread images on the tracings)
This was from a kit shipped early August 2025.
Just reporting in. Thanks to all the contributors.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Chiming in here with the same issue which I have just resolved today. I had 2 z axis motors moving together and one moving slightly more than the other 2.
I've wasted plenty of time measuring, tracing z screws, printing tubes, measuring angle with a digital level etc and contacting support. Some were more helpful than others. The screw thread is clearly different on some motors. I have a feeling there is an 'old' and a 'new' spec or supplier. You just need 3 of the same!
In the end I bought new motors myself (I bought the 'Stepper motor Z-axis right' with the longer cable although it was a 'left' one I was replacing. It was a hunch that these might be matched to my other good ones). The first I ordered was the same spec as my dodgy one - It travelled about 1mm further than the other 2. So I ordered 2 more which are both correct (the same as my 2 other good ones). Fitted one today and now all 3 motors / screws are the same and printing consistently without a skew.
I have been speaking with support and I do have someone helpful who understands the issue. I'm hopeful I will be reimbursed for the motor and the other 2 I didn't use I will just return.
Bit of a faff but I don't mind the tinkering if it works out well. Maybe this is acceptable to some people but it was wrong to me. I'm hopeful Prusa will acknowledge this properly to help others.
I believe this skew issue also contributes a lot to the known issue of bed levelling - where users are fitting spacers to affect the z calibration. Mine is pretty good without any spacers fitted now.
This tool was actually very helpful: https://www.printables.com/model/1543676-tool-to-check-the-pitch-of-the-z-axis-spindles-of
- Thank you to Muk for making that. It allowed me to quickly check the threads of the new motors before fitting.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Also having the issue, video with levels showing the live change
Support suggesting defective trapezoidal nuts and they'll send two replacements to try
Hopefully it's an easy fix,as having to manual continue prints for the bed alignment failure is quite annoying
RE: Skewed XY-Plane (Z Rods, Heatbed)
Found some spare nuts I had on hand. Swapped out the left and right nuts, potentially made it slightly worse. Back to support chat and see if i can get some motors
RE: Skewed XY-Plane (Z Rods, Heatbed)
Also have this issue. I got my Core One Assembly Kit in August and it has printed without issues for a couple hundred hours. A few weeks ago I had trouble with an electric discharge in bigger prints leading to blue screens. That issue seems to have been eliminated thanks to a tip from Jürgen.
My skewed heatbed only happens occasionally, however is happening more often and especially on prints in which I have an added pause (for adding NFC-Chips or manually changing the filament). After unpausing it often gets skewed, even though the initial print went fine.
When I manually move the Z axis with the controls it mostly evens out and stays quiet, however during prints, especially at the beginning and the end, the Z axis sometimes seems to hit a resonance frequency and the rods wobble and become loud.
I am unsure if it is the same issue, related or not at all, just leaving this here first and will also message support.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Found some spare nuts I had on hand. Swapped out the left and right nuts, potentially made it slightly worse. Back to support chat and see if i can get some motors
Yeah they tried that with me first, even though I don't think anyones solved the issue without replacing 1 or in my case 2 motors. You have to be persistent with them, send them a link to this thread...they will send you out motors eventually.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Same for me. Support was convinced initially that I was experiencing step loss caused by ill-fitting nuts. The argument that convinced them otherwise was that if you let the bed move all the way up and down a few times, the deviation does not accumulate (as step loss would), but comes back to its starting point after every cycle.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Found some spare nuts I had on hand. Swapped out the left and right nuts, potentially made it slightly worse. Back to support chat and see if i can get some motors
Yeah they tried that with me first, even though I don't think anyones solved the issue without replacing 1 or in my case 2 motors. You have to be persistent with them, send them a link to this thread...they will send you out motors eventually.
Yeah first agent was fairly dismissive even when I linked this thread, second agent was great and disappeared for 15 minutes to read through this whole thing, then came back and started a case for my issue with the Coreone specialists and sadi to check back in after the holiday. He agreed with the motors being the issue although hard to say which one.
My back left bed is super high, front right low. I believe it to be the right motor, he thinks the back one