Too Much Tension MMU2S Extruder Idler for MK3S+
Hey everyone. I have an MK3S+ with the MMU2S installed and now I need to print TPU (Overture brand, 95A). I know FLEX is not supported by the MMU2S and have read about the common issues printing TPU with MMU2S in the loop. Even so, I spent the night trying to get it to work. Ran into a few of the usual issues, such as filament winding around the MMU2S bondtech gears, so after a while I decided to unplug the MMU2S and feed the TPU directly into the extruder. The problem is that even with the lightest possible tension on the extruder idler I am unable to push the filament in far enough to trip the IR sensor. Filament autoload was not working because of this so I tried manual filament load. The gears grab the filament and it streams through the nozzle nicely, but the IR sensor still reads 0. I tried adjusting the IR sensor again, but that did not help. Anyone else have this issue? I'm thinking about using a slightly longer screw for the tensioner, or possibly printing a new tensioner door with a deeper hole for the nut so I can get a few more threads to play with. Hoping I'll be able to get the tension light enough for this filament. I need to be able to print flex/TPU somehow, even if I have to unplug the MMU2S. This is really disappointing because autoload was working with the same filament before I installed the different idler door/chimney/sensor tower for the MMU2S.
RE:
Good news! I printed the modified extruder idler with a deeper hole for the nut which allowed me to release even more tension. Now I can push the Overture TPU filament through enough to trip the filament sensor, and I currently have a print going and it is looking good. Is it okay to share the model? I started with the mesh for the part provided by Prusa and modified from there. Next step will be to hook the MMU2S back up and see if it still works, but not until I have a few successful TPU prints using the MMU2s extruder idler.
Edit to add: I did use the screw pulling technique to pull the nut into the stock extruder idler as much as possible, but it was just not deep enough for the idler screw to catch threads before the spring had been compressed too much for the TPU. The part I created has the nut quite deep, ~3mm from flush, but it works.
RE:
My take on manually feeding TPU with MMU2 installed is: remove the PTFE between MMU2 and extruder, make some other filament available in slot 1 of the MMU and just start the print using this slot (MMU single mode), MMU2 will load the filament into mid air, the moment the filament would reach the extruder insert the TPU into the extruder (extruder will load, since it expects the filament from the MMU2), press in the flap in the extruder chimney with your finger to safely trigger the IR sensor (stable signal is only needed for loading, as soon as loading ist finished and the extruder starts to move you can release the flap since the IR sensor signal is ignored during printing without load or unload process of the MMU2), at the end of the print the extruder will unload the TPU and the MMU2 will retract the air loaded filament and you just have to reinstall the PTFE and everything is back to normal.
Edit: make sure spool join is selected off and filament sensor is selected off in LCD menu.
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RE: Too Much Tension MMU2S Extruder Idler for MK3S+
Update: When I hooked the MMU2S back up using just my updated extruder idler it was still having issues sensing the filament when fed by the MMU2S and filament would still get wound around the MMU2S gears, just couldn't dial it in. I then tried printing an updated IR sensor holder ( https://www.thingiverse.com/thing:3554066 ) and MMU2S selector ( https://www.thingiverse.com/thing:3608229 ) which are supposed to be better for TPU but they did not work smoothly right away and I would have to spend some time cleaning up the parts, might have to reprint one, etc.. so I decided to put that aside for now. There is a youtube video of someone assembling those updated parts, but unfortunately it is in German so I may have missed some important tips.
My take on manually feeding TPU with MMU2 installed is: remove the PTFE between MMU2 and extruder, make some other filament available in slot 1 of the MMU and just start the print using this slot (MMU single mode), MMU2 will load the filament into mid air, the moment the filament would reach the extruder insert the TPU into the extruder (extruder will load, since it expects the filament from the MMU2), press in the flap in the extruder chimney with your finger to safely trigger the IR sensor (stable signal is only needed for loading, as soon as loading ist finished and the extruder starts to move you can release the flap since the IR sensor signal is ignored during printing without load or unload process of the MMU2), at the end of the print the extruder will unload the TPU and the MMU2 will retract the air loaded filament and you just have to reinstall the PTFE and everything is back to normal.
Edit: make sure spool join is selected off and filament sensor is selected off in LCD menu.
I need to get started on a few TPU prints, so tonight as I am typing this my printer is working away using your suggested method. Thank you for the suggestion. It is not ideal, but at least allows me to keep the MMU2S hooked up while I print a single color TPU part, which is really all I need.