MMU3 on MK4S - Trouble Extruding
Issue: When printing with the MMU3, I keep running into an issue where filament quits coming out of the nozzle after a few layers. The extruder starts to click and then the extruder stalls out. I can visually watch the roll stop spinning and the print continues on as if it's extruding but nothing is happening. Looking for help on what is causing the extruder to bind up/get stuck and why the printer isn't detecting it.
Background: This weekend I added an MMU3 to my MK4s and have only one successful print. Immediately after the print, I made two 5mm cubes and it appeared to work. Anything since then, has not worked. I usually can get a couple layers down depending on the object I'm making but then the extruder quits. I have many hours on this MK4S and it was working before the upgrade. I am using a known good spool of polymaker pla pro that is dry. For the model, I'm just trying a basic cylinder to make sure it works.
Everything appears to be working:
- I can unload the MMU3 and it feeds to the extruder. Same with unload.
- All calibration has passed.
- Checked the idler screws are at the proper setting.
- Made sure my nozzle was seated properly (loosened, dropped, and reseated it)
- Made sure my extruder cover was not too tight, I backed it off.
- Redid the gears calibration, it appeared to pass.
- I can preload the MMU3 and send filament all the way to the extruder. When I eject the filament it looks like the below pictures.
- After ejecting, cutting the stretched piece of filament, I can load the filament. The MMU sends the filament through to the extruder and it comes out in a bit of a blob then extrudes like normal.
The first line and even some of the first layer seem to come out fine depending on the size of the print but eventually the clicking happens and the extruder stalls out. This is what the filament looks like after unloading it and ejecting it from the MMU3.
Please let me know if you have ideas. I've been trying to read up on common issues and attempting to troubleshoot myself but I'm stuck and could use help from the community. Thanks!
RE: MMU3 on MK4S - Trouble Extruding
Did you check if the teeth from the transport mechanism in the MMU3 have ground a groove into the filament? This sometimes happens and the MMU3 can't transport the filament any further because the rest of the filament is too thin there. Pull the filament out and look at about 40 cm from the end if there is a big groove. Cut it off there and load the filament back into the MMU3.
RE: MMU3 on MK4S - Trouble Extruding
Sounds like you may have too much drag in your PTFE tubing. Avoid sharp bends; MINIMUM radius is about 75mm.
Do you have “Stuck Filament Detection” enabled?
MK4S/MMU3
RE: MMU3 on MK4S - Trouble Extruding
@walter-layher - Thank you for the help! I have a groove about 70 mm back. I cut this and tried to print again. Same thing happened, the groove appeared again. Here is a picture of what it looks like:
After cutting the same thing happened. My print stalled out here:
And I ended up with the groove cut into the filament. When I look at this groove and where it sits, I seems to line up with the extruder in terms of height.
@largriff - Thank you for the help as well! I definitely had the radius tighter than that 75mm in my first setup. I moved the printer and mmu3 to print up some more space and I was able to print my test shape- 25cm diameter, 5 cm height cylinder. Unfortunately, when I went to run the larger print, I ran into the same issue as before. As a test, the filament moves pretty easily from the buffer cartridge to the mmu3 but there is quite a bit of resistance from filament roll to cartridge. I'm wondering if I need to go even wider and try and minimize the restriction from filament roll to the buffer cartridge. Here is my setup after moving to a spot with a bit more space. Will try a wider table next.
RE: MMU3 on MK4S - Trouble Extruding
Also forgot to mention. I do have the stuck filament logic turned on but each time this has occurred, I have not received a stuck filament detected warning.
RE:
Yeah, if the extruder is grinding your filament, you need to tighten the two tension screws at the top of the extruder. The extruder should stall, before it slips.
MK4S/MMU3
RE: MMU3 on MK4S - Trouble Extruding
Ok, I double checked the tension screws again on the top. Still having issues getting the MMU3 to work. I've spent a lot more time trying to diagnose.
Following up on the stuck detection not working, I went back to try and recalibrate the finda and filament sensor. I can calibrate the finda but I am unable to calibrate the filament sensor. The test just fails. I pulled apart the extruder and verified assembly and made sure the magnet was installed in the new swivel assembly. I verified that the tension screws are set correctly as well, they are right up to the face as per the instructions. Going to focus on the filament sensor and see if I can figure out why that cannot be calibrated.
RE: MMU3 on MK4S - Trouble Extruding
Wanted to follow up and share that this was resolved. After working with Prusa support, they pointed out I missed a step in assembly. I did not update the idler arms to the new idler arms included with the MMU3. This was a user error and I made a mistake here. The MMu3 requires the new geometry in order for the filament sensor to work correctly. You need the filament sensor to be functioning for proper MMU3 operation.
Thank you for the help above! Sorry for the time waste. My takeaway from this is to go back through the instructions and double check each step.
RE:
The original Idler has lot of Issues, espacilly that the idler springs is blocking the Idler senor arm from moving freely!
To solve all idler issues and really use multi material I designed and evalute a new Idler over the past months
it will eliminate your issues:
https://www.printables.com/model/1269218-nextruder-mmu-multi-material-gamechanger
Greets Thorsten
