MMU3 Filament swaps causing debris in the Extruder?
I've been battling a problem now for nearly two months, I've been in contact with support and while they had offered some suggestions (which I tried) and I don't think it's the correct course of action, for example they wanted me to reduce the filament maximum flowrate, why do this when it's been working perfectly for months? I plan on going back to them again soon now I have a little more free time.
"So what's the problem?"
After a few months of FLAWLESS multicolour printing, printing large objects with thousands of colour changes my prints started to fail, filament stopped loading, prints would pause with "Load to Extr. Failed", something initially I could solve with a quick angled snip of the end of the filament end during the next load and then feeding it into the extruder. Eventually, I found that the extruder itself was filling with little bits of filament that would need cleaning out to allow the print to continue. This is not normal and not how it performed before.
So what changed?
Near when this started I did have a print fail due to the filament being stuck and not being able to be ejected from the extruder but that seemed to be a minor thing, so much so I'm not completely sure if it lines up timeline-wise properly with when the issue first started. The only other change was I swapped to an Obxidian Nozzle for a while but that was switched out when I first started having problems (just in case) and it had been performing great before hand with the Obxidian, handling big prints with thousands of colour changes. The filament is also the same brand I have been using for a few years so no change there either.
I have taken apart the extruder a couple of times so far and cleaned it out, re-greased it, etc. to make sure it's all working fine inside. I also cleaned up any dust and ensured the filament path was clean and straight in the MMU3. I've tried tweaking a few suggested settings for the Toolchange Parameters in the filament settings, but they didn't seem to fix the issue with filament bits in the extruder, so it's now back to standard(ish) settings.
I cannot figure out why the Nextruder is filling up with bits of filament.
My filament ends appear to be good, if anything they were slightly thick and stumplike and I've changed some settings to get them a bit more elongated to see if that was the problem as my thought was that small bits of the filament was being shaved off when trying to be inserted into the nozzle, this has slowed down the creation of the filament pieces and I can get a lot more of a print completed before there is an issue so there may have been some truth to that
I'm now at a loss, I don't know what to try as everything 'appears' to be ok, but if it was, why is my extruder filling with filament and causing print fails?
RE:
There are settings in PS under filaments, advanced. In that tab there is a section called Toolchange parameters with single extruder mm printers.
In that section there is ramming parameters. This is specifically there so that you can mash the tip of the filament before a filament change to try and eliminate that small amount of debris that your getting. My guess is that debris comes from the end of the filament when it retracts out of the extruder.
I have no idea how to adjust it as I have an XL, but I knew it was there from researching the settings.
I'm not sure what your filament profiles look like, but usually the Prusament profiles are a good starting point if your using a quality filament.
RE: MMU3 Filament swaps causing debris in the Extruder?
I'm familiar with the single extruder toolchange settings, I've been tweaking them over the last month or so trying to solve this issue, unfortunately, there appears to be next to zero instructions out there for how these various settings will effect the creation of the tip etc. There's tooltip information in Prusaslicer saying what each setting does, but little out there that will give actual examples of the effect so there's a lot of people out there testing with trial and error trying to figure it out.
For example, in your reply above you say "This is specifically there so that you can mash the tip of the filament before a filament change to try and eliminate that small amount of debris that your getting". This is exactly what I've been trying to do but there is little to no information out there that will help with WHAT parameter will have WHAT effect.
I've been running tweaked the Ramming Parameters for a few weeks so that the Total Ramming Time is reduced to 1s, this seemed to have helped a little, but certainly not solved things.
RE: MMU3 Filament swaps causing debris in the Extruder?
I am stuck on the MK3S+, so this does not come from a place of authority. The bearings in your picture have dirt on them. That dirt may be causing issues where the gear can't properly grip the filament, or where it may be gripping the filament too tightly. I'd clean them off with some IPA. The teeth on the extruder gear also have a "line" of what looks like wear on them. (Between the red lines on the attached image.) That could be normal (again, I'm stuck in MK3 land), but seems a bit odd to me.
RE: MMU3 Filament swaps causing debris in the Extruder?
Thanks for the info, I've been periodically cleaning the teeth as they get bits and pieces in them due to all the filament debris, I hadn't noticed any waer on the gear teeth but that is certainly something I'll take a closer look at now, thank you.
RE: MMU3 Filament swaps causing debris in the Extruder?
It was just some food for thought. I have seen when changing filament on my mk3s+ where there is a string with a ball on the end of the filament when unloading, in particular with PLA. That's what made me think the issue might be from unloading the filament vs. loading, although I've not seen the same issue on my MK4 or my XL.
You said that it used to work fine, but now it doesn't. Is it possible that your nozzle is worn. Have you printed any abrasive filaments? I have heard that glow and silk filaments can be more abrasive even though you wouldn't normally put those in the categories of abrasive.
RE: MMU3 Filament swaps causing debris in the Extruder?
Around the time I first noticed the issue I had two incidents/changes, first was a swap of the nozzle to the Obxidian , which I swapped out once I started having the issue to eliminate it as a potential problem. The second issue is that I had a filament jam, the filament inside the PTFE from the MMU3 unit got twisted due to not enough vertical clearance with a tall print (which is now sorted). I don't know for sure how close these events happened to when I started noticing issues, but it would have been around the same time I think, I wasn't paying that much attention.
RE: MMU3 Filament swaps causing debris in the Extruder?
@FIB, I also was having that issue, until I realized, that filament path and the grove in the bearings are not aligned which causes bend and malformed filament. Due to the filament can be bended now to edges, it is possible that abrasions, espacially if not completly hardedend, can be leftover in the filament path.
Also the idler with the original main-plate does not completely fit together, the idler is blocked by a not rounded edge close to the hinge of the idler.
I did redesign the main plate and put there some extra infomations and improvements that causes that issuses for load and unload filaments, Take a look:
https://www.printables.com/model/1059347-mk4mk4s-with-mmu-main-plate-with-improovement-step
Since nearly 2 weeks or respectively more than 2500 filament changes, I didn´t had any load unload issue, caused by the extruder.
Greets Thorsten
RE: MMU3 Filament swaps causing debris in the Extruder?
It's good to hear I'm not the only person having an issue like this, this looks like an interesting solution and one I will investigate, thank you.