Blockage troubleshooting.  

Re: Blockage troubleshooting.

Rafael.d

No. What I am saying is that the PTFE I received in my original MMU was the wrong size. I actually tried a couple others from Prusa as well, but while waiting for the new MMU PTFE to arrive from Prusa I measured the ones I had been using. All measured between 2.1 and 2.2 mm ID and one of them (I can not be sure which one) was the original one sent in the MMU. The new MMU PTFE I received from Prusa 11/22/17 measures 1.85mm ID. I installed it, and the printer is working well as we speak.

Re: Blockage troubleshooting.

I invested my precious coffee break today to unscrew my heatbreak from the heatsink. Boy was that thing stuck, 2xM6 nuts locked together + 100°C oven and a lot of force did it in the end. There was no filament in the thread though. I have photos of both ends of the heatbreak showing all the tapered bits, if anyone's interested I can post them here.
Now I'll try reseating everything as PJR suggested, hope that helps.

Re: Blockage troubleshooting.

Spoke too soon.

Well I'm back to square one again. Managed to get a few decent prints in MMU mode done and my spirits were lifted. No longer.

So PR sent me some replacement parts, I have a black printer. Points for guessing which colour the sent me?

So at prestent my Printer is in peices. I have replaced the extruder using my recently purchased thermal paste, the PTFE tube has been replaced with a new one from PR. The Multiplexer and Extruger carage have been replaced. I'm half way through replacing the the Extruder motor assemblies & idlers. Then I have to replace the thermistor as it broke during the disassembly.

I have noticed by pusing a length of filament through the four multiplexer tubes that there is an obvious tight point in the rear right. I need to investigate further but I am also reluctant to as I am sick to death of taking it apart to troubleshoot.

Re: Blockage troubleshooting.

I want to say this again and more clearly: Some of you may have received improperly sized PTFE tubes in the multiplexer. I did.

If the blockages you are having are between the top of the PTFE tube and the metal cooling tubes in the multiplexer and if the ends of the filament are too thick to retract into the cooling tubes, your PTFE tube is larger than the 1.85mm ID that it is supposed to be. This was the main cause of the problems I had and it wasn't until I discovered a way to measure the ID of the PTFE that I was able know enough to order new PTFE from Prusa and fix my problem. I tried to explain this in my 3 earlier posts on page 26 of this forum.

Along the way I picked up a lot of good hints from PJR. Keep it up if you are still monitoring this.

Re: Blockage troubleshooting.

I measured mine (delivered end of october) and the diameters are fine. However, I had to cut it as it was 1mm too long. After reseating with PJRs procedure I can definitely say the MUX slides on easier. It feels like I lost about 1/2mm of play. Honestly, since you can't check it once it's assembled and there's no way to quality-control the process besides trying a long MM print, why not deliver it disassembled? You could supply a little clip to screw the hotend to the carriage when the front plate is off.
I haven't had much time, but I have since printed a single color Marvin and at least the quality has not decreased. Tonight I'll tune all my springs to minimal tension, then maybe a new multicolor attempt if I can stomach it.

Re: Blockage troubleshooting.

OK, I printed a solid flat slab in 0.3 mm with the PLA I use most (Sakata Ingeo 830). During print, after observing each layer, I loosened the extruder screws until gaps clearly appeared between lines in the layers, then tightened back about 1,5 turns. I managed to get a very shiny & smooth surface.
Rinse and repeat for all extruders. Some observations:
1. indents on the filament are now hardly noticeable
2. no more skipping, I'm printing a Marvin right now and it looks neat (half through). That wasn't possible before unless I used original Prusa PLA.
3. spring tension is much less than I anticipated, far less than the 4-5 mm they mention in the build manual !
4. the visible length of the springs sticking out of the printed parts differs massively between extruders. Either the springs themselves have loads of tolerance or it's the printed parts. I have variations of 2 mm
5. the sweet spot for spring tension seems to be much smaller than I thought. It is within one full turn, a bit too much or too little and visible gaps appear between the lines.
6. Something for malcinator: After I had dialed in the first extruder, I noticed my live Z jumping...back to my original good value I had before the MMU upgrade. Changing to the next extruder (not dialed in) it jumped back, then back to the old value after setting the springs. Same for 3&4. I have no explanation for this, only a theory that it's either some pressure buildup propagated from the bondtech thats pushing the hotend around (duh..) I had clearly set all spring tensions too strong on 1-4, by approximately the same amount. Or it is a sign of underextrusion, i.e. you need to press down layer 1 more to get it to stick (more likely).
7. the PJR procedure for reseating the PTFE clearly increased print quality, I recommend doing that first in case of problems.

Next I'll do test prints on all extruders, then jump in the ice cold water of 4 color prints yet again.

Re: Blockage troubleshooting.

Epic.

Now I have almost completed the installation of the Orange Parts on my Black Printer. Not only is it Multi Material it is now Multi Coloured. Not the look I want but if it works then great. I've mamaged to snap the wires off the thermistor when I was disassembeling the hotend, I'll be ordering a new one from E3D later for now have a bodged fix in place. Also I need more cable ties and I've snipped of almost all of them now removing the thermistor.

This is a total epic.

Re: Blockage troubleshooting.

Yes, indeed. I have had a frustrating week trying to dial in my filament. In fact I can print now on all extruders my testing rectangle in any size, as fast as I want and with any layer height.
Still, as soon as I print something that needs retracts it fails. I'm dead sure about my print temp, and I've tried all possible retract combinations between 2mm length 20mm/sec and 5mm length 50mm/sec. The prints look beautiful, until they fail - consistently and always at the same layer. Always with the same blob right below the PTFE.
I wanted to swap out my fan anyway for a 40mm Noctua, so maybe I'll also try that even though it's working perfectly.
Also I noticed that my filament is consistent thickness, but more around 1.7mm instead of 1.75. I don't know what impact that could have but I'll try to increase the extrusion a bit. Prusa PLA seems to print ok, but I've only got the original silver spool around and cannot source the stuff here.
Right now I'm running out of options. I have about 20kg of that filament around, if I cannot dial it in at all my mood will really drop.

Re: Blockage troubleshooting.

Try r3ducing the retraction to say 1.5mm and possibly reducing temperature too

Retractions were killing my prints with mmu.

Regards Joan

Re: Blockage troubleshooting.

Thanks Joan, I'll try that. 1.5 seemed to be too extreme to try but I guess if it works for you it's worth a try. Meanwhile I tried every other filament I had around, all with Prusa PLA settings:
Polymaker Polymax (small sample I had around): works
Fillamentum PLA: works
unbranded random PLA: works
unbranded PETG (generic PET settings): works
old and dried out ugly color esun I bought because it was dead cheap years ago: works (at this point I wanted to throw the printer out the window)

The only thing that won't cut it is the stuff I use for everything and of which I have every color around (and which is labeled by opening date and kept in a dry box to preserve). That just sucks.

Re: Blockage troubleshooting.

Well I give up on the filament. I could print beautifully in single mode with basically everything else I had around, always at default settings for the material. Maybe I'll just get another printer to print off what I have, then sell it again. Will try MM prints next, but I'm optimistic now that it is finally reliable in single mode.

Re: Blockage troubleshooting.

Hi, just to share my experience. I tried to print with Unicofil PLA Rainbow. I had 3 failed prints by blockage between the PTFE tube and the heat-breaker in single filament mode. The last one was at 205°C and no retraction at all in Slic3r settings. So I tried to re-seat the PTFE tube and now it fails every time halfway through the "first layer calibration" bundled in the firmware. Every single time blockage between the PTFE tube and the heat-breaker. I then switched to a white ColorFabb filament and no problem at all.

So maybe it's just me, but Unicofil PLA Rainbow filament doesn't work with this machine. I even used a caliper and the diameter seemed very consistent.

Re: Blockage troubleshooting.

I looked up Unicofil and they say on their website it is based on Natureworks Ingeo with embedded corn starch. So the basis is exactly the same as for my Sakata Ingeo, which has absolutely great tolerances as well. Just speculating, but maybe the problem is with the distribution of the embedded starch fibers. If this is irregular, it would lead to differing friction and melting points within the filament. Bottom line: stick away from Ingeo with the MMU.

Re: Blockage troubleshooting.

I have prints failing all the time now, in single extrusion mode. If I use multiple colors and switch a lot no problem, but a single color print fails after a couple of layers with a blockage just below the ptfe tube. I can simply remove the tube, cut the blockage and restart printing, only for it to happen again after a couple of layers.

It's driving me nuts. No idea what's going on, I already lowered the PLA temperature a couple of times but the problem remains.

If anyone wants to have a shot, here is the file that consistently fails on me, it uses extruder 1:

Re: Blockage troubleshooting.

Itˋs about bloody time someone from PR comments on this. At least acknowledge something is wrong.

Re: Blockage troubleshooting.

I am getting super fed-up with this issue at this point.

I've tried every conceivable slicer and slicer setting.
I've tried inconceivable slicer settings.
I've rebuilt the entire hotend.
I've ordered replacement heatbreaks, ptfe tubes, steel tubes and paid the huge shipping costs.

Lately, I can't even get 50% of my single-filament models to print anymore. I almost wonder if this is essentially a heat-creep issue. I think my next step will be to break into the extruder design and super-cool the heatsink. But I'm not hopeful.

I really hope Prusa and Co. haven't responded because they've been busy fixing the issue and any day now they will swoop in with the solution. Or more likely, they're putting Mk3's in boxes... I would've ordered one myself, but this MMU has soured me lately.

Re: Blockage troubleshooting.

I would've ordered one myself, but this MMU has soured me lately.

Signed. In fact that was my plan since it was obvious that some flexibility and quality would be lost when installing the MMU. If it somehow worked reliably at least with PLA/PETG/PVA, I'd eventually move towards a second printer. But not at this point. What's most frustrating is that I know it can produce great 4-color quality, my demo prints look awesome.

Re: Blockage troubleshooting.

Hello all,

I want to thank the people here for the extensive discussion about the MMU's blockage issues. Like many here, I made the mistake of thinking that my extensive experience printing with a single extruder (and some dual-head dual extrusion) would make the MMU work easy.

I think the most important thing for me was to do serious failure assessments and extensive printing until I 'got it'. In the end, the main key for me was playing with temperatures. Even though I use exclusively filaments.ca filament, almost every different colour has its own temp. I start with 205/198, and then go up and down as necessary depending on the blockage. Until now, I have tried about 10 colours, and I would dare say only a couple worked without modifying the temperature. up or down 2C.

How do I do my failure analysis?

I start at 205/198 and then go until failure. Once that happens, I take out the filament that failed and look at it. If it has a hair, then I reduce the temp. If not, then I increase the temp. Repeat until success, and then lock down that number for that filament in a filament profile.

Like you, I wish there were more information about this. I think barring this, my advice to Prusa Research is: Just call this an "advanced" user or "professional" upgrade or "beta" product. I WANT Prusa to keep working on this. I had a Prusa i1 and it was freaking hard. But the constant work and feedback and input gave us the mk3. We are in early days for multicolour printing. This is the Gestetner. I want PR to keep working on it. At the same time, I can see why users feel betrayed: Not many people expected to buy this thing and spend hundreds of hours learning multicolour printing.

Thank you to PR and to all of you for the community.

tarek : )

Re: Blockage troubleshooting.

I have had the mm printer since November 28th. For the first few weeks I printed 4 color objects with no issues. The last 2.5 weeks I get a clogged steel tube in one of the 4 chambers. It is never the same one. I have reduced the temp to 200 as suggested by Peter. I have emailed Prusa multiple times, and have yet to get a suggested solution. What would cause the printer to degrade within a few weeks? Of course, 1 color prints fine. 2 color , sometimes, 3 color maybe (2 out of 3 whale prints), 4 color fails after 3-4 hours due to a clogged steel tube. BTW, I got to page 28 before throwing out a help post. Filaments used are Hatchbox, Atomic, and Solutec.

Re: Blockage troubleshooting.

Hello all,

I have been reading through this forum looking for an answer and unless I missed it I havent come across anyone with the same problem I have been facing, I have a MK2/S with MMU1.0 and I keep getting a jam right before the heatbreak. It seems as though the filament is too larger to enter the Heatbreak to melt again. When I start the print I snip all the filament ends and they load fine and run the pre print wipe fine, but then after a few filament changes, boom, jam. The filament just wont load into the heatbreak to melt, it will try to print and nothing will come out, then it goes to change color again and the other filament will load, sometimes it wont. Like I said i have been looking and reading through this forum hoping for an answer or something to try. Please if anyone has anything i would love to get this working. Thanks in advance!