RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Kinda wish I’d bought an inclinometer instead of a small level now, they’re only a few £/$/€ more.
So am I right in thinking as long as the motors are mounted correctly, and there’s no damage or bending to the lead screws themselves, any tilt is going to be the result of mismatched lead screws?
I guess damaged/worn trapezoidal nuts could be a factor, or skipping steps due to binding, but both of those seem highly unlikely here.
I really wish there was a way to identify the out of tolerance screws easier than the tracing method, my first attempt at that did not yield very good or convincing results 😂
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
You can use a clinometer app; for example, ClinoScope on iOS provides 0.01° resolution and displays the tilt digitally. I’m not sure whether there’s an equivalent for Android, but there’s likely a similar option.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Hi Albert, it was really your concern about layer adhesion which threw me off. As long as we are talking about a linear distortion of the overall object shape, we are on the same page.
As an aside, it would actually be possible to compensate for this skew in firmware -- even with all three motors wired in parallel. The software-based bed leveling correction already moves the bed dynamically during the print, as a function of X and Y. It would "only" need to be enhanced to move as a function of X, Y, and Z: As the print progresses, there would be a gradually increasing contribution which compensates for the tilt caused by the screw pitch difference. It would be difficult to calibrate though: It can't rely only on automated bed probing, but needs to know the screw pitch difference in addition.
But let's not go down that rabbit hole. It looks like Prusa has decided not to go for software compensation, but rather provide replacement screws to the limited number of users who notice this flaw.
Glad we converged 🙂
Yes, I completely agree, mechanically correcting the root cause is by far the cleanest solution. Software compensation would quickly become complex and fragile compared to simply having matched screws.
Thanks for the thoughtful discussion - it helped clarify the different models.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
So am I right in thinking as long as the motors are mounted correctly, and there’s no damage or bending to the lead screws themselves, any tilt is going to be the result of mismatched lead screws?
I guess damaged/worn trapezoidal nuts could be a factor, or skipping steps due to binding, but both of those seem highly unlikely here.
Tilt that changes gradually and reproducibly as the bed moves up or down will be due to the lead screw pitch.
In addition there is the "static tilt" between the base plate and the CoreXY mechanism, due to frame/chassis build tolerances. And it seems to be somewhat common that the tilt changes due to step loss of a motor: When I approached Prusa support about my lead screw issue, they were at first assuming that I was experiencing step loss, and it took a while to convince them otherwise. The difference between the two is that tilt due to screw pitch differences will be fully reproducible and reversible when you drive the bed back to its origin, while the effect of step loss will keep accumulating.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Another question Jurgen 😂 Im asking you because youve been through this exact process .
When they sent you the motors, were they all the type with the long cable?
Im asking because in the Core One spares section on the Prusa site, they have 2 motors...Stepper motor Z-axis left (short cable) and Stepper motor Z-axis right (long cable)
In my email from DHL, it clearly states:
Description: MK4 motor Z axis left
Do you have record of exactly what they sent you?
I really don't see why they need to confuse things and have 2 different versions, just for the sake of a few extra inches of cable.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
I could have sworn that Prusa support only sent motors with the long cable -- first a single one, and then three more. But looking at my left-overs after the swap (which Prusa did not want back), there are three "left" motors with the short cable and one "right" with the long cable. So they must have sent a mix of the two variants.
It's probably best to wait and check whether you get a motor with a matching thread, then start worrying about cable lengths. Worst case, you can always cut the cable off the swapped-out motor and solder or crimp it to the new one. (Have some heat-shrink tubing ready...)
For the Core One, where all motor cables are hidden in the base anyway, I agree that Prusa could have made their own life easier by standardizing on a single cable length. I assume the two different lengths go back to the MK4 and allow for a tidier cable routing there?
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
I could have sworn that Prusa support only sent motors with the long cable
Yeah thats what support told me also, but I have my doubts now looking at the email from DHL.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
@jurgen-7 So since you've resolved your tilted bed issue, did you ever go back to check the z accuracy now? By printing the tall cylinders next to the lead screws?
Only reason I ask is from what I can gather from @petulf post here:
https://forum.prusa3d.com/forum/prusa-core-one-hardware-firmware-and-software-help/skewed-xy-plane-z-rods-heatbed/paged/5/#post-759753
Isn't it right to say he in fact had 2 out of tolerance leadscrews?
Has anyone got round to actually checking the pitch on the motors they're currently sending out ?
RE:
@jurgen-7 So since you've resolved your tilted bed issue, did you ever go back to check the z accuracy now? By printing the tall cylinders next to the lead screws?
Only reason I ask is from what I can gather from @petulf post here:
https://forum.prusa3d.com/forum/prusa-core-one-hardware-firmware-and-software-help/skewed-xy-plane-z-rods-heatbed/paged/5/#post-759753Isn't it right to say he in fact had 2 out of tolerance leadscrews?
Has anyone got round to actually checking the pitch on the motors they're currently sending out ?
I have not printed the test cylinders (neither before or after the replacement), but have relied on the "pencil rubbing" measurement of the lead screw pitch. I did measure the replacements before installing them.
Lite @petulf, I originally had two lead screws that were too "fast", and one pretty exactly at the nominal 2 mm pitch. The first replacement Prusa sent had the nominal pitch as well. The next set of three new lead screws were all "fast". Go figure...
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
That's my situation I think. I printed 3 250mm cylinders close to the lead screws:
Left is bang on 250mm, rear (centre cylinder in picture) and right are 251mm.
So I guess if you printed the same cylinders you'd have all 3 at 251mm?
If the Z dimensional accuracy was absolutely critical on a large part, where would you compensate for that?
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
So I guess if you printed the same cylinders you'd have all 3 at 251mm?
If the Z dimensional accuracy was absolutely critical on a large part, where would you compensate for that?
Yes, that's the result I would expect.
Unfortunately PrusaSlicer does not offer global scaling corrections in the printer settings, which would be the right place to correct for this. So I would have to apply the correction in the print-specific settings (object scale factors in the lower right of the plater view; "unlock" to enable independent factors in X/Y/Z). Not ideal, but at least I can correct the height for critical parts, in contrast to the skew created by the original, differing screws.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
I find it quite strange that Prusa are still providing these motors out of tolerance.
If you were lucky enough to get a printer with all three motors within tolerance, and then for whatever reason needed to replace a motor, you'd likely end up with a bed that tilts.
Am I being pedantic here? Just seems a bit odd for a company that uses dimensional accuracy as a selling point for their printers.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Yes, it seems like Prusa are handling this poorly.
I could understand a sudden change of pitch at some point in the supply history: A change of supplier, a supplier changing their tooling or whatever. If, throughout the history of the i3 printers, there had never been a problem with different screw pitches, there may not have been a tight, agreed-upon specification on that part. (Yes, there would have been a specification if this were about medical equipment or passenger aircraft... But realistically, in the world of consumer products or other devices which are not heavily regulated, it is pretty common that tight specs are only defined once it has been realized that they are critical.)
Hence, something like the MK4S-to-Core-One upgrade mismatch may have been difficult to avoid. But it seems that Prusa are either still receiving lead screws with different pitches, or are sitting on a large inventory of old parts with mixed specs -- and can't be bothered to measure them. Or at least roughly sort them into two or three classes, which should be quick and easy with a suitable custom gauge.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
Am I being pedantic here?
Biting back a sarcastic reply, I'm not getting this either. Endangers a reputation for reliable accuracy that was earned in products not through polished marketing material: The fact that this relates (largely?) to the special case of kits upgraded with a 3rd Z-axis motor may go unnoticed by the casual buyer...
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
The fact that this relates (largely?) to the special case of kits upgraded with a 3rd Z-axis motor [...]
That is incorrect. Many full kits seem to be affected, which is not surprising since they combine a pre-packaged MK4S-style motor set with a separately packed third motor.
And I recall at least one report of a factory-built printer to be affected as well. I did find that surprising initially, but given that the spare parts Prusa sends out seem to be a random mix of thread pitches, their inventory just seems uncontrolled in this respect.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
---That is incorrect. Many full kits seem to be affected... at least one report of a factory-built printer
You're making me nervous...
I put together a thread gauge, here on printables. Obviously, XY scaling of the printer needs to be correct.
So far I did only basic testing with the 100% version but it seems to work as intended (locks into the spindle, if at both ends simultaneously with only a little extra force).
RE:
---That is incorrect. Many full kits seem to be affected... at least one report of a factory-built printer
You're making me nervous...
I put together a thread gauge, here on printables. Obviously, XY scaling of the printer needs to be correct.
So far I did only basic testing with the 100% version but it seems to work as intended (locks into the spindle, if at both ends simultaneously with only a little extra force).
Mine was a full kit also, batch one , and I'm 100% affected.
And I too made a tool similar to yours which locks onto all the threads on all the rods, so I instantly dismissed this as an approach....because as I said, I know I'm affected.
Spirit levels dont lie.
The only tool that I could see that would be effective would be a long precisely machined nut covering a good percentage of the entire rod, I'd say 50% of it to be sure. Any drift in tolerance of the leadscrew would result in binding when spinning the nut on. Of course this is out of the reach of the average user, but should be well within reach of the largest 3d printer manufacturer in Europe.
The easiest way for the average user who doesn't want to go down the route of tracing/counting pixels etc would be the 3 cylinder test....just make sure you have a ruler with mm markings to hand.
My 3MF is attached (I think)
All cylinders should be of equal height if your 3 lead screws have matching pitch , all cylinders should be equal and 250mm if your 3 lead screws have matching pitch and are within tolerance.
Calibrate z before running test, and remove any shims or anything else that some people have installed.
I honestly believe that many people have this issue and aren't even aware.
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
@jurgen-7 They sent me the wrong motor 😂
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
@jurgen-7 They sent me the wrong motor 😂
Wrong thread pitch, so you now have two each of the two different pitches? Or a short cable where you need a long one? (Or both? 😉 )
RE: Different Z lead screw travel between MK4S upgrade screws and Core One kit — 2 mm mismatch
@jurgen-7 They sent me the wrong motor 😂
Wrong thread pitch, so you now have two each of the two different pitches? Or a short cable where you need a long one? (Or both? 😉 )
Wrong cable, pitch is perfect...when I line them up side by side the pitch in my suspect one drifts out very noticably...I lack the photography skills to capture it, I could bodge the wires but I'm in no rush.
They've just shipped me the correct one. Just hope the pitch is good. PITA but what can you do 🤷♂️