MMU Works for a "while"
I've gotten a few really nice prints off the MMU but I've had a lot of frustration as well. I've had an intermittent problem with the tips being to large to go back into the heat break. At least I thought it was intermittent but I think I'm starting to see a pattern. After I've had the extruder apart, I seem to get a good print or two out of it and then then the large tips start to return. It seems like I get 100 to 200 filament changes and then I start to have problems. It doesn't matter if it is a few short prints over a couple days or 200 changes into a single 500 tool change print.
I've done a lot of reading through the forum and initally thought it was the heat break PTFE tube migrating up out of the heat break over time. I've printed a locking clip for the connector there and measured the amount sticking out, on initial assembly and on tear down after issues and I'm pretty confident its not moving.
I "fixed" it for a while by drilling out the heat break to 2.2mm and replacing all the PTFE tubes from the MMU selector to the nozzle with ~2.0 mm ID cheep PTFE tubes. I ran it for a week and got some pretty good prints out of it. I still had some issues with the filament getting stuck between the MMU drive and the selector when the tips started getting big, but it was minimal and I think swapping out those PTFE tubes with larger ID ones would solve that. The "slop" in the feed did cause my print quality to suffer some but it wasn't horrible. This however seemed like kind of a brute force solution and about a week ago I went back to the stock setup.
Since switching back I've really started paying attention to when the larger tips started showing up. Even with the stock setup, default settings on PLA, a couple different brands, the tips will start out very nice and then eventually they get bigger and start jamming. They almost always feed all the way down to the heat break but will not pass the smaller diameter there. At that point the tips will be 2.0 to 2.1 mm. The first few dozen changes they would be around 1.9 and pretty perfect. Restarting the same Gcode that had 100 great tips, will result in the first tips being to large on the next print. Once they have gotten big, I've realized that no changes on the slicer filament side seem to make a significant change in the OD of the tip. I can get them more or less stringy or have a nicer point on them, but they all are to big. It has always been something that I've attempted to change that has required me taking apart the print head that make the tips go back down to the correct size and make me think I've finally got it nailed down. Every time I've had it apart, cleaning up the path, replacing the PTFE tube with a new chambered (correct ID) one, changing the relationship between how far the heat break and tip are threaded into the heat block, swapping the R3 parts that came in the box for the ones that I printed... etc... These all seem to fix it for a while.
I don't seem to see anything that is working loose when I disassemble it. Everything it tight, aligned how I assembled it, and everything that I can find on the forums to check seems within tolerances every time I take it apart.
I'm kind of running out of ideas. I don't really want to go back to my over sized print path as a fix. Does anyone have any more suggestions?
I3 MK3 MMU 2.0.
Re: MMU Works for a "while"
First of all lowering the temp and increasing the cooling runs might help a little bit.
Second one of possibilities is too much extruded filament. Means the whole filament what should be extruded is not, so it's building a higher pressure inside the nozzle. You can see it if you print only a small wall with one color, so there is no healing possible (like on the support or infill). It helps to lower the multiplier if you print small MM object with many color changes, so less plastic is being extruded.
Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram
Re: MMU Works for a "while"
I attempted some of the above suggestions and many others with the stock MMU setup and never saw any consistency. The patterns above, where I could print shorter prints well, did seem to hold for another couple weeks of messing with it in the stock setup. I've switched back to a full 2.2 to 2.5mm path from the MMU to the nozzle and am getting near perfect prints. I'm in the middle of my 3rd 24hour + print since switching back and the only issue I've had was a tangle at the spool holder that caused a miss feed. My tips are fat, in the 2.0 to 2.2 mm diameter but they happily feed through the larger path without issue.
I'm pretty happy with this as a solution, just kind of annoyed that others seem to be able to make the stock setup work.
I3 MK3 MMU 2.0.
Re: MMU Works for a "while"
Are you using the MK2.5 or MK3?
I wish I could remember where I read it on the forums, but someone was reporting that they were having trouble with the MK2.5 and the tips getting too large. I can't quite remember what their solution was, but during the assembly process, they skipped a step or didn't swap out a part (heat break maybe?). But after going back and swapping in the correct part on the extruder, it started printing consistently.
Sorry to be so vague, but maybe it will pop up in the search results.
Re: MMU Works for a "while"
Are you using the MK2.5 or MK3?
I wish I could remember where I read it on the forums, but someone was reporting that they were having trouble with the MK2.5 and the tips getting too large. I can't quite remember what their solution was, but during the assembly process, they skipped a step or didn't swap out a part (heat break maybe?). But after going back and swapping in the correct part on the extruder, it started printing consistently.
Sorry to be so vague, but maybe it will pop up in the search results.
I hope we will not get the big comparison between models again. There are so many different reports/results even from MK3+MMU2. If everybody will start to make his current MMU2 issue to a MK* model issue, it will get very hard to give helpful hints and tips.
Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram
Re: MMU Works for a "while"
Mine is a MK3. I did follow the mk2.5 to mk3 heat break thread for a while and did drill out one heat break to 2.2mm. I'm still using that one now. I've put back in an unmodified one several times and have generally had better luck with the larger one. I bought a set of gauge drill bits that have very fine steps between ~1.9 to 2.2 in 4 drill bits. One option I'd thought about was stepping between 1.9 and 2.2 at the very bottom of heat break where it is in the heat block (the hot portion). I thought that might help with inserting the larger tips but I never got around to it. The one that is 2.2 all the way through seems to work well for me.
I3 MK3 MMU 2.0.
Re: MMU Works for a "while"
Has there been any more on this problem? I am experiencing big tips causing jams. I have replaced all the PTFE tubes with 2.0mm ID but still have issues. I can successfully load a filament to the nozzle if has a clean cut. But after unloading it, the tip is too big and when I try to load to the nozzle again, one filament jams at the heat break and another one jams at the filament sensor. If I cut the tips off at this point, I can easily push the filament through and get it to feed. Since this is happening with the menu, I'm guessing the printer is using some sort of default cooling/ramming values so making changes in a slicer wouldn't do anything.
Re: MMU Works for a "while"
Has there been any more on this problem? I am experiencing big tips causing jams. I have replaced all the PTFE tubes with 2.0mm ID but still have issues. I can successfully load a filament to the nozzle if has a clean cut. But after unloading it, the tip is too big and when I try to load to the nozzle again, one filament jams at the heat break and another one jams at the filament sensor. If I cut the tips off at this point, I can easily push the filament through and get it to feed. Since this is happening with the menu, I'm guessing the printer is using some sort of default cooling/ramming values so making changes in a slicer wouldn't do anything.
it's doing the same thing on all filaments? default settings can work just fine. I am default settings and stock hardware.
I have a Prusa,therefore I research.
Re: MMU Works for a "while"
it's doing the same thing on all filaments? default settings can work just fine. I am default settings and stock hardware.
Each filament is a bit different, but the end results are the same. The default settings results in a tip that is too big to make it back to the nozzle.
Re: MMU Works for a "while"
do they move freely in from the selector to the extruder? it's gotta be something after the selector I would think.
or are the plastic covers that holds the 5 PTFE tubes too tight maybe?
I have a Prusa,therefore I research.
Re: MMU Works for a "while"
do they move freely in from the selector to the extruder? it's gotta be something after the selector I would think.
It makes it to the filament sensor reliably. After that, it jams somewhere between there and the nozzle. Normally at the heat break, but sometime before it reaches the bondtech gears.
I have seen that there is a special heat break for the Prusa that is not a standard E3D heat break. What is the difference between them? I'm wondering if mine might not be the special one. I got the printer before the MMU 2 was released.
Re: MMU Works for a "while"
something else to check is the long pyfe tube connector, i swae mine started mushrooming out abut. i had to fike the inside of it abit. but i coukd hear a "click" as it passed the connector, so i had a slight hint
I have a Prusa,therefore I research.
Re: MMU Works for a "while"
something else to check is the long pyfe tube connector, i swae mine started mushrooming out abut. i had to fike the inside of it abit. but i coukd hear a "click" as it passed the connector, so i had a slight hint
Not sure which tube you are talking about. The one from the MMU2 to the extruder or the one in the extruder before the nozzle? In either case, I have replaced both of those and still have the same problem.
Re: MMU Works for a "while"
the connector for the ptfe tube going from the selector to the extruder. life has been very calm after finding that pain in my ass. but it seem everyone has something different to fight with. but it would get hung up on that abit, then wouldn't make it to the extruder after that. stupid missed layers. funtn thing was only filament path 1 would snag on the connector.
I have a Prusa,therefore I research.
Re: MMU Works for a "while"
the connector for the ptfe tube going from the selector to the extruder. life has been very calm after finding that pain in my ass. but it seem everyone has something different to fight with. but it would get hung up on that abit, then wouldn't make it to the extruder after that. stupid missed layers. funtn thing was only filament path 1 would snag on the connector.
The filament isn't getting hung up anywhere along the path. It just get blocked because of the tip. When I manually push the filament through, you can feel it get blocked and by measuring the amount fed in, it is at the heat break where the blocking occurs. If I cut the tip off, then the filament feeds through easily and makes it through the nozzle.
Re: MMU Works for a "while"
maybe the filament isn't able to move as freely as it should, during the ram/cooling moves.
I have a Prusa,therefore I research.
Re: MMU Works for a "while"
The filament isn't getting hung up anywhere along the path. It just get blocked because of the tip. When I manually push the filament through, you can feel it get blocked and by measuring the amount fed in, it is at the heat break where the blocking occurs. If I cut the tip off, then the filament feeds through easily and makes it through the nozzle.
If your MK3 is more than a couple months old....Did you replace the PTFE tube inside the extruder per the MMU assembly instructions?
Older MK3s had a PTFE tube with a wider inner diameter, and that can cause fat tips.
Re: MMU Works for a "while"
The filament isn't getting hung up anywhere along the path. It just get blocked because of the tip. When I manually push the filament through, you can feel it get blocked and by measuring the amount fed in, it is at the heat break where the blocking occurs. If I cut the tip off, then the filament feeds through easily and makes it through the nozzle.
If your MK3 is more than a couple months old....Did you replace the PTFE tube inside the extruder per the MMU assembly instructions?
Older MK3s had a PTFE tube with a wider inner diameter, and that can cause fat tips.
After speaking with support about this some, it turns out that I did not get the special Prusa heatbreak with my MK3. In regards to the PTFE tube, I don't remember, but if it was in the instructions, then I did replace it.