Getting ready to chuck my MMU3, constant layer shifts on color changes
Figure I'd try again to see if anyone else might be having problems or better yet answers ever since I made apparently the horrible mistake of updating my printers and perhaps prusaslicer about 2 months ago. My MMU3 worked great, more or less, using an older MK3S+ firmware with an older version of Prusaslicer (what ones I don't know, I know the prusaslicer was at least an update or two behind and the MK3S+ even older, MMU3 was maybe 1 behind), but ever since I updated everything I've had nothing but nightmares. For the record, this issue DOES NOT AFFECT MONO COLOR PRINTS, THEY COME OUT PERFECTLY FINE; it only seems occurs when colors change from one to another. If going from one to another and back again, it seems to realign based on whatever color is in that slot. Same scenario if I use 3+, except it gets progressively worse in shifts. So I can't say it's the firmware updates solely, and I'm perplexed as to why.
I've gone through this guide ( https://help.prusa3d.com/article/layer-shifting_2020) so many times and nothing has helped. Originally it was just shifts on the X axis, but now I've noticed it's been slightly creeping on the Y axis as well now, so another headache added. In order on the guide, I've tried over the last 2 months:
1. Check your printer’s power mode: it was actually in stealth mode before unknown to me, I've since swapped it to normal. Thing is, it apparently was working fine in stealth before, and normal has made no difference
2. Make sure the extruder and the heatbed can move freely: Nothing at all impedes it, there's no random bits of filament trapped or anything, and as far as I can tell the cable bundle doesn't hit the printer sides when printing. Otherwise if it were the issue would've been apparent a hell of a lot sooner. Rods have been lubed.
3. Check your X/Y axis motors and pulleys: Tightened as hard as I can in the correct way show in the diagram and in the recommended position, several times in fact since when asking this question here and elsewhere, this was the most common suggestion and one I've also had issues with on a different machine before. One grub is on the flat, the other on the rod. Aligned as far as I can tell, looks straight and doesn't wiggle left or right. Plus if this was truly off, my monocolored prints would be exhibiting layer shifts, and they have not.
4. Check the tension of your belts: Can't count how many times I've done this stupid step. The MK3S+ has the belt self test, so I've primarily used it. I tried the tuner webpage before but it constantly says the X axis is too lose and wants me to tighten it way over to the point that it isn't "springy" at all (as in I can't pinch the two rows together), so I assume it is giving me false readings as printing with it tightened to the app's recommendation didn't return a good print. The weird part is both the tuner webpage and self test both agree my Y axis is tensioned correctly, so I never got why they were both so far off on X axis. Also did the thing where you grip the one rod on the motor with pliers to check for looseness, there is none, it doesn't jump, etc. Again if this was truly off, my monocolored prints would be exhibiting layer shifts you'd think, and they have not.
The guide from there goes into Mini and XL troubleshooting, which is irrelevant since I have the MK3S+.
I've also tried adjusting the position of the spools numerous times trying to reduce any perceived tension in them to lessen any chance of friction affecting them; while I can't do their "ideal" layout in the manual since I definitely don't have a table that large to waste on it, it was printing fine initially and for a while in a far less optimal spool layout/arrangement than what I've swapped it to and around a few times now, and I've never had any issues with it failing to advance filament through the tubes no matter the configuration. So I don't think this is playing any effect on my current woes. Cleaned it numerous times of old filament bits and fluff, made sure all the pulley grub screws on it were aligned and tightened, etc.
If anyone at all has some other suggestions or things to try, I'm all ears. Otherwise I'm just assuming that Prusa still makes a pretty crappy multimaterial unit and to consider other options in the future. I mean if I can't even get this fixed again and working on an older MK3S+ model, I'm even less confident it'll work whenever I get a Core One and it gets MMU3 support, which sucks since I have a lot of side business printing that uses multicolor prints now, so losing this capability would negatively impact me.
The MK3S+ has the belt self test, so I've primarily used it.
The belt tension figure is a measure of the resistance felt by the stepper when moving the axis. On a correctly set up machine this does equate, roughly, to belt tension.
But other things can affect mechanical resistance.
First, with the power off, move the axis by hand; is it smooth? Does the resistance stay the same over the whole range?
Clean and lubricate the smooth rods, check they are not damaged/scratched. Check the idler pulley is not clogged, out of line, or damaged (loosen the belt and try turning it with your fingertip, is it smooth?)
With the belt loose try turning the stepper motor by hand; is it smooth?
Retighten the belt until it just begins to make a low musical note when plucked...
Make your next print this:
https://www.prusaprinters.org/prints/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus
It MUST be printed in Prusament PETG or the spring tension will be wrong.
Let us know how you get on.
Cheerio,
RE:
Yes X-axis moves smoothly (at least it feels like it to me). No scratches I can see on the rods. Tried lubing them before also. Printed the tension meter and confirmed that I'm not crazy and that both belts fall in the good range, so at least for me that means I should trust the belt self test and not that dumb app.
I mean all of your advice sounds good if I was getting layer shifts in everything, but again I'm only getting layer shifts when a color change happens through the MMU, you'd think if the belt was off or any of these other issues were occurring it would affect the entire print and not just when a color change happens (mono color prints are fine). So I feel after having done all of those checks and calibrating before many times now, eliminating all possible things on the things on the printer, it has to be either MMU or firmware related?
The MK3S+ has the belt self test, so I've primarily used it.
The belt tension figure is a measure of the resistance felt by the stepper when moving the axis. On a correctly set up machine this does equate, roughly, to belt tension.
But other things can affect mechanical resistance.
First, with the power off, move the axis by hand; is it smooth? Does the resistance stay the same over the whole range?
Clean and lubricate the smooth rods, check they are not damaged/scratched. Check the idler pulley is not clogged, out of line, or damaged (loosen the belt and try turning it with your fingertip, is it smooth?)
With the belt loose try turning the stepper motor by hand; is it smooth?
Retighten the belt until it just begins to make a low musical note when plucked...
Make your next print this:
https://www.prusaprinters.org/prints/46639-tension-meter-for-the-gt2-belts-of-i3-mk3s-or-prus
It MUST be printed in Prusament PETG or the spring tension will be wrong.
Let us know how you get on.
Cheerio,
OK, a bit of a long shot: undo the ends of your PTFE tubes and try pulling some filament through them - are some of them worn, or clogged with filament dust, so adding resistance to the feed?
Cheerio,
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
I did check them before actually and they seemed ok. Yeah some had a bit of filament dust I blew out but nothing that would really impact filament going through them. They didn't seem damaged outside of the tiny pinching from where the collets grip them, nothing unusual though.
OK, a bit of a long shot: undo the ends of your PTFE tubes and try pulling some filament through them - are some of them worn, or clogged with filament dust, so adding resistance to the feed?
Cheerio,
Pull some filament through to check for internal wear.
Cheerio,
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Filament goes through fine.
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
So something else I have noticed now that I'm thinking about it, loading filament has actually been a real pain in the last couple of weeks; I don't know why, but when I push the filament through the tubes, the idler will grip and advance it, but it won't either get to or trigger the...selector I think it's called? It'll just sit there doing nothing, eventually I pull the filament back out, and it just takes numerous tries sometimes before it'll finally load. Thinking now this might be a possible cause as well, so looking at the old assembly manuals trying to figure out the best way to rip it open to look.
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Tore off the selector finally, didn't see any blockages or reason why filament wouldn't be passing smoothly. All tubes are clear honestly, all things in the idler aligned, everything tight. Dunno what the hell is up quite frankly.
I guess I can try flashing all the firmware again but everything I try feels like beating a dead horse since apparently no one else has these issues or everyone has since ditched the MK3S+ with their MMU units.
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Have you watched the print process while doing colour changes? The thing I would immediately suspect is the print head striking a blob on the wipe tower and getting knocked out of alignment, causing the layer shift. I don't see why people are suggesting friction in the filament path - that won't cause a layer shift although it could cause under extrusion or other issues.
I also would suggest starting from a completely vanilla set of default presets, slicing your file, ensuring the printer you select is MK3 with MMU3. I'm wondering if the upgrade somehow caused the profile to be altered so it doesn't have the correct settings for multi-colour prints.
Prusa MK4 since Jan 2024, Printables: @MikeB_1505898
RE:
Yeah I have watched it and have observed it shifting off to the left for no discernable reason during a color change. Never seen any blobs formed on either the wipe tower, the print itself, etc. I never use grid infill either, just throwing it out, always rectilinear or gyroid. As far as I can tell I'm just using the default generic PLA profile on all of my prints as well in prusaslicer., I've never really made any custom ones besides ones that just up the temp for my silk filaments (which so far, it's been erroring out on just generic profiles as well as the one upping the temp for that specific filaments). Otherwise the x axis isn't colliding or hitting anything, belts are tensioned right, doesn't seem to be skipping, etc etc.
I think I may just re-flash the firmware on both MMU unit and printer just to see if maybe somehow it got corrupted when I flashed before? And maybe just downgrade in versions just to rule out it being that as an issue at all, or maybe I'll hit an older combination where it works.
I did notice another oddity relating to my loading problems from above, I don't believe the selector is centering itself correctly on my MMU? I mention this because I've tried manually moving it to the right a touch during load fails and it has a much better path it seems to load if I do that. But it's not like I can change anything on how the MMU3 does that. So another mystery I suppose. I double and triple checked, there isn't any filament bits or dust causing a blockage, I disassembled it late last night after all and triple checked any tiny bits were removed or blown out.
Have you watched the print process while doing colour changes? The thing I would immediately suspect is the print head striking a blob on the wipe tower and getting knocked out of alignment, causing the layer shift. I don't see why people are suggesting friction in the filament path - that won't cause a layer shift although it could cause under extrusion or other issues.
I also would suggest starting from a completely vanilla set of default presets, slicing your file, ensuring the printer you select is MK3 with MMU3. I'm wondering if the upgrade somehow caused the profile to be altered so it doesn't have the correct settings for multi-colour prints.
RE:
Tried downgrading the firmware of both printer and MMU3. I will say that downgrading the MMU3 firmware did at least seem to alleviate loading issues, at least when I tried now it seemed much better.
Layer shifting on color swaps is still a thing. I've been trying 2 different scenarios, one with a small item where I change color on the extruder based on height, the other I paint it on. It is significantly worse on any color changes it seems when I paint areas for different colors, it is very noticeable. In contrast, for ones doing a color change on the extruder based on height, it is minimal to not noticeable right now (and I say that because before I did all the various tweaks above, it was shifting more noticeably).
So yeah I'm still at a loss, and no one else here seems to have any other ideas. Is there any way I can ask someone actually at Prusa these kinds of questions or to have them take a look here? As outside of just fully tearing it apart and rebuilding it, it otherwise is just tempting to smash it on the ground and consider the evil rival instead...
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Another new weird update; I was finally able to get a non-shifted print, but in order to do so I had to do the print in "numerical" order; basically starting with the black filament loaded in the first extruder, then the MMU swapping to the second extruder white one, and then it makes its changes back and forth just fine (see top print).
In comparison, any print I tried in the reverse order starting with the white filament in the second extruder and swapping to black in the first extruder and so on, resulted in a shift as seen in the bottom print (it's probably not as clear but you can see where a big shift occurs right at the point where the initial color swap takes place, and the other side bulges out as well).
I don't know what the hell is going on. Filament order never mattered before for the MMU when printing, so why does it now shift when I start with the one loaded in the second slot compared to the first slot? Makes no sense. I even camped out watching it, it's not colliding with anything, it just finishes printing the one color, does the second, swaps back and then goes "oh, maybe I'll print a mm or two over to the left". Just frustrating. ANYONE KNOW WHAT MIGHT BE CAUSING THIS THAT I HAVEN'T TRIED ALREADY?!
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Here is an idea for fault isolation, now that you have a setup that replicates the problem in one case and not in the other, if you swap filament positions you should be able to isolate if this is hardware or software. The idea being is that if you still see that you need to print them in numeric order this is independent of which filament is in which position and any interference from the software since the software is the only system that knows which color is in which position. If the opposite is true you now know this is a software or setting issue.
/Anders
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Well nevermind, had to swap filament since the colors I had in were getting low, now the motherfucking thing has gone back to shifting. Ugh.
Here is an idea for fault isolation, now that you have a setup that replicates the problem in one case and not in the other, if you swap filament positions you should be able to isolate if this is hardware or software. The idea being is that if you still see that you need to print them in numeric order this is independent of which filament is in which position and any interference from the software since the software is the only system that knows which color is in which position. If the opposite is true you now know this is a software or setting issue.
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
How the fuck can I contact someone at Prusa directly to ask them why their piece of shit MMU3 had decided that layer shifting on color changes is cool? They obviously don't monitor their own forum boards, and no one else unfortunately seems to have this issue, so they can't offer any advice. I'm seriously about ready to say fuck this ecosystem and go with the evil Bambu one, if their AMS at least works half as reliably as this piece of shit Prusa puts out, I'll suck up a locked down ecosystem from an evil chinese company as long as it'll let me get back to printing so I can resume orders that need it.
one else unfortunately seems to have this issue,
I'd say that is fortunate...
Contact Prusa via Support Chat. On the Company page select Contact Us.
You will need the serial numbers of your MMU and printer.
Cheerio,
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Prusa do not monitor the boards, as you've stated, although they do seem much more active over on the Github pages, so you could maybe try posting there? Saying that, the best method to contact Prusa support is via their online chat as suggested by Diem above.
I hope this gets resolved for you soon, I know how frustrating it can get when something happens for no reason out of nowhere. Please do keep us posted.
--> MK4 - MK4S - MINI+ - MMU3 - Accelerometer Guide - BambuLab A1 Combo <--
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Just throwing this out there.
i had a very consistent abnormality happening during color changes on my MMU3 (MK4S).
during every color change, my MMU3 would unload fine and then load the next filament into the nextruder. i watched the sensor/idler shift to the left, then the MMU3 idler would rotate to allow the filament to free spool. the carriage / print head would transition to the right side above the purge tower. at this point the filament would unload. the extruder gear would spin for a couple seconds and completely unload the filament. the sensor/idler would shift back to the right. from here it would (try to) purge and (try to) print normally. every color change. all 5 slots loaded with prusament PETG of diff colors. tried all colors. different orders. 100% same result. first color prints with no issue and then the filament loads / unloads during every color change.
i can say with 100% certainty that during a color change, as soon as the filament loads and the carriage transitions to the purge tower, at this point it executes the "end G-code" in the filament profile (Custom G-Code).
i used this to retract the filament at the end of prints to reduce/eliminate oozing. (works like a champ)
on a side note, it was interesting that once the filament unloads like this, there is no error. the printer goes about trying to print as though the filament is loaded. and yes, the sensor is calibrated correctly and shows no filament on the LCD.
as someone recommended above, try using default (un-edited) profiles for the printer, filament, and print settings.
would have saved me a couple days of trial and error.
RE: Getting ready to chuck my MMU3, constant layer shifts on color changes
Unfortunately I've used nothing but their default print profiles in prusaslicer, the only things I might tweak are like infill %, if I want scarf seams or not, etc. on their default profile. I don't know a thing about gcode manipulation.
Just throwing this out there.
i had a very consistent abnormality happening during color changes on my MMU3 (MK4S).
during every color change, my MMU3 would unload fine and then load the next filament into the nextruder. i watched the sensor/idler shift to the left, then the MMU3 idler would rotate to allow the filament to free spool. the carriage / print head would transition to the right side above the purge tower. at this point the filament would unload. the extruder gear would spin for a couple seconds and completely unload the filament. the sensor/idler would shift back to the right. from here it would (try to) purge and (try to) print normally. every color change. all 5 slots loaded with prusament PETG of diff colors. tried all colors. different orders. 100% same result. first color prints with no issue and then the filament loads / unloads during every color change.
i can say with 100% certainty that during a color change, as soon as the filament loads and the carriage transitions to the purge tower, at this point it executes the "end G-code" in the filament profile (Custom G-Code).
i used this to retract the filament at the end of prints to reduce/eliminate oozing. (works like a champ)
on a side note, it was interesting that once the filament unloads like this, there is no error. the printer goes about trying to print as though the filament is loaded. and yes, the sensor is calibrated correctly and shows no filament on the LCD.
as someone recommended above, try using default (un-edited) profiles for the printer, filament, and print settings.
would have saved me a couple days of trial and error.