RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
I did it by homing and moving the X-carriage (from menu) (nozzle on the left and back center) and rotating the spindle so that the nozzle touches, and then everything is level... there's nothing you can do, one driver is causing problems, we need 3 drivers, then move all 3 spindles and hom... then you'll have everything level.
If you are talking about a "static" tilt (which is due to a tilt between the printer's base plate and the CoreXY plane), you can correct that by adjusting the mechanical bottom end stops near the three lead screws. Either insert M3 screws into the three tapped holes in the base plate, or use plastic shims of suitable thickness around the lead screws. (There are various models on Printables.) Then the Z calibration, which drives the bed into the bottom stops, can make the bed parallel to the CoreXY plane, and you don't have to readjust manually after a Z calibration.
But if the pitch of the three lead screws is not the same, then neither your method nor the one I described can fix this.
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I did it by homing and moving the X-carriage (from menu) (nozzle on the left and back center) and rotating the spindle so that the nozzle touches, and then everything is level... there's nothing you can do, one driver is causing problems, we need 3 drivers, then move all 3 spindles and hom... then you'll have everything level.
If you are talking about a "static" tilt (which is due to a tilt between the printer's base plate and the CoreXY plane), you can correct that by adjusting the mechanical bottom end stops near the three lead screws. Either insert M3 screws into the three tapped holes in the base plate, or use plastic shims of suitable thickness around the lead screws. (There are various models on Printables.) Then the Z calibration, which drives the bed into the bottom stops, can make the bed parallel to the CoreXY plane, and you don't have to readjust manually after a Z calibration.
But if the pitch of the three lead screws is not the same, then neither your method nor the one I described can fix this.
I've got the shims in my printer just as a crude improvement over the obviously non-aligned default endstops. The M3 screws are a good idea, just make sure nothing gets overstretched (there is quite a bit of leverage as the screw is > 40 mm away from the spindle. If it works, great, I didn't like the tension when it runs into the endstops during calibration.
In everyday operation I always keep it level it by manual spindle adjustment per the quote. Just routine diligence, it avoids skew between X, Y with the Z axis (in theory - I'm not claiming to print anything where you'd notice).
Printers with three and four individually controllable motors do exist but of course someone needs to pay for it. But honestly, I always thought I had paid enough - when I understood the Original Prusa approach with co-wired steppers I didn't know whether to laugh or cry...
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
That approach is good for the front 2, but not any good for the rear leadscrew.
In that case the best is a digital clinometer
Agreed 100% 👍
What was the outcome with yours? Did you contact Prusa?
Yeas, I sent Prusa the photos of the digital inclinometer readings: 0.00° at the bottom (Z=275) vs. 0.35° at the top (Z=0).
To confirm the mechanical failure, I also flagged that for the exact same turn count, one POM nut travels 275 mm while the other only reaches 273 mm.
Support agreed with my findings and a replacement assembly is already on its way. I expect it in 2–3 days.
I'll keep you posted once I get the new parts installed.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Support agreed with my findings and a replacement assembly is already on its way. I expect it in 2–3 days.
Fingers crossed that the replacement will have the correct thread pitch! 👍
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Fingers crossed that the replacement will have the correct thread pitch! 👍
In any case, I will have six units in total, so I think I’ll be able to try different combinations until I find the ideal one. I hope so. 🤔
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Oh, so they are sending you a complete set of three right away? Great, that should take care of it.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
I ended up with good match of three. I think I'm in the same boat as Jurgen where I ended up with 3 that are matched but are likely out of spec, and 2 that are matched and in spec. Obviously I've fitted the 3 that match.
A bit annoying, I haven't decided whether to push this further. I still don't understand how they've got so many out of spec motors and why they're still sending them out..
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
>> good match of three
That wouldn't bother me too much. Z shrinkage needs to be calibrated in any case unless maybe PLA if filament doesn't shrink at all with elevated chamber temperature.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
>> good match of three
That wouldn't bother me too much. Z shrinkage needs to be calibrated in any case unless maybe PLA if filament doesn't shrink at all with elevated chamber temperature.
Surely Z shrinkage is always going to be tiny in comparison to any X/Y shrinkage? (When assessing a finished part?)(presuming z pitch is within accepted tolerance)
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
A bit annoying, I haven't decided whether to push this further. I still don't understand how they've got so many out of spec motors and why they're still sending them out..
The problem is not that they are out of spec: there was a rather old post where a tolerance was mentioned by someone in support and they are all within it. The problem is that different production batches (or maybe even multiple suppliers) have different tolerances and mixing them creates the issue.
It seems that, even after this issue was found, Prusa never managed to get enough time out of all the work they are doing to check all their motors and group them into compatible groups.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
>> good match of three
That wouldn't bother me too much. Z shrinkage needs to be calibrated in any case unless maybe PLA if filament doesn't shrink at all with elevated chamber temperature.
Surely Z shrinkage is always going to be tiny in comparison to any X/Y shrinkage? (When assessing a finished part?)(presuming z pitch is within accepted tolerance)
yes, I usually don't correct. But if (per the subject line) my printer were 2mm off over its height, then I'd probably set it up for the default profiles
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Maybe to clarify what I meant with "needs to be calibrated in any case", then "I don't bother to calibrate":
The point was, the absolute Z accuracy of the printer does not directly translate to the print. The material is printed at slightly higher (average) temperature, then cools down and shrinks a little bit. For a dimensionally accurate print, yes, I should look into it. But the correction is less (say, going from 35 °C chamber temperature to RT) than XY shrink, where the much higher numbers for nozzle and possibly heat bed temperature factor in.
So there is a correction factor in the system which I'd use anyway for dimensional accuracy, therefore I wouldn't care too much. As long as all three Z motors are off by the same amount (if not, the resulting skew cannot be corrected as easily).
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
The replacement set of three stepper motors and lead screws has just arrived. Prusa didn't even ask for the defective units back, which speaks for itself.
It looks like I have plenty of work for the weekend; replacing these parts is quite 'entertaining' given the amount of disassembly required on the Core One.
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I found it easiest to swap the motors with the printer laying on its back (door and top cover removed). But place some support to ensure that the printer does not rest on the WiFi plastic cover!
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Make sure they all match before doing all that work ! There’s no guarantees…I found the right motor they sent (long cable, for rear of core one) to have incorrect pitch compared to the left motor they sent (short cable).
if you now have 6 motors, you are bound to have a set of 3 that match.
Also I found no reason to take the sides off like they recommend in the online guide.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Make sure they all match before doing all that work ! There’s no guarantees…I found the right motor they sent (long cable, for rear of core one) to have incorrect pitch compared to the left motor they sent (short cable).
if you now have 6 motors, you are bound to have a set of 3 that match.
Also I found no reason to take the sides off like they recommend in the online guide.
Actually, there's a very simple way to verify if they match before doing all that work. You don't even need to install them in the printer.
Just place the motor on the table and manually thread a POM nut. If it takes exactly 34.75 turns to travel the full length of the lead screw, the pitch is correct.
If they all reach the same point with the same number of turns, you are good to go.
I’m not taking the sides off either; I’ll find a way to swap them without a full teardown. I have 6 motors now, so I will definitely find a matching trio among them.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
@jurgen-7 posted a great quick guide (I think in this thread) and it's really not too bad. Now I've done it a couple of times I can do it really quick without even thinking.
If you only need to replace the rear motor for any reason, its super quick as you don't even need to remove the display or bottom skirts.
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@jurgen-7 posted a great quick guide (I think in this thread) and it's really not too bad. Now I've done it a couple of times I can do it really quick without even thinking.
If you only need to replace the rear motor for any reason, its super quick as you don't even need to remove the display or bottom skirts.
Your comment reminded me of something from many years ago.
I used to work in software & hardware design for a multinational, and in our labs there were large posters on the walls with just one word written in big letters: SERVICEABILITY!
The message was simple: when you design a product, you must also design it for the poor field engineer who will eventually have to repair it.
If a motor fails, replacing it should take minutes, not half a day and half the machine.
Sadly, that philosophy seems to have faded over the years.
Many products today are clearly designed for manufacturing efficiency, not for maintenance.
So whenever I see a machine where a component can be replaced quickly and without dismantling half of it, it feels like a small victory for old-school engineering.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Just as info for this thread, I just finished my MK4S to Core ONE upgrade that was shipped on 2/24/26. My leadscrews were fine. I checked them with the pencil/paper trick first and then printed 3 cylinders. The height measured by a digital caliper was within .1mm( printed at 260mm). I also printed a layer across the bed, and the 1st layer is perfect. My MK4S upgrade kit was from 2024. I don't know if the issues are fixed or I got lucky with a good batch.