Filamentgrinding issue probably caused during unloading  

RE: Filamentgrinding issue probably caused during unloading

Does your filament properly leaves the bond tech gears of the extruder before the MMU try to unload? If not, make sure the IR sensor (chimney) is triggered correctly, this is the single most critical sensor for the MMU to work properly.

RE: Filamentgrinding issue probably caused during unloading

Yes, there did not seem to be any problem with the extruder gear. Not even with the MMU until it starts speeding up when the filament tip is a few cm above the extruder.

I had my fair share of issues with the IR sensor as well but printed out a modified extruder idler where the tick that triggers the sensor is a tiny bit longer. Since then I have had no issue with the IR sensor, also not with filaments that compress more than PLA.

I have found a major issue though which was certainly responsible for a lot of failures. The two screws locking in the MMU idler body where loose. Not loose enough that it did not work at all but loose enough for ever increasing failures as the counter wheel was not in the correct place and therefore the grip of the MMU was probably weak, no matter how I set the tension screws on top.

I will need to test now if that I resolved the above issue or was just another problem on top of it all.

RE: Filamentgrinding issue probably caused during unloading

I had issues that were similar and I addressed it a couple of days ago. The idler barrel on the MMU was warped and caused this issue by changing the position that the MMU thought the barrel was in.

To verify this, turn off the steppers on the menu or power down the printer. Open the MMU up and spin by hand the idler assembly. If there is any wobble there, then you either have to contact tech support or print your own. I printed a new barrel placing the old parts on the newly printed piece and have had nothing but great luck since. Well, luck no, it was bad luck to receive a defective part.

Those two screws on the idler axis that attach to the idler motor must be in the correct position as well to ensure that the MMU stays where it should.

RE: Filamentgrinding issue probably caused during unloading

I think the barrel is ok with mine. I am currently printing my first >1000 tool change print.
I had some issues for the first dozwn changes or so but that was probably due to remaining PETG in the hot end. The tips were really stringy and ugly even though I used the standard settings. After a few tool changes it suddenly turned nice as expected and there was only a single manual intervention otherwise so far: one of the filamens slipped out of the back of the MMU. That's an error I have not quite fully understood yet. Maybe I had the MMU idler tension too high so there was the low risk of moving filaments that were not selected just a bit. It was probably not the FINDA probe as that one should work fine now after I exchanged the selector for that neat selctor mod with magent for the FINDA ball on thingiverse.

I am still waiting for my 2.5 mm ID tube. I suppose the system should get a lot more robust towards tip issues with that.

I hope I am not saying it too early but my MMU2S is starting to get usable also for regular sized prints.

RE: Filamentgrinding issue probably caused during unloading

Sounds fantastic! I got to this point as well but a new problem came up. Since I have reduced almost all drag I was getting filament tangling due to a rocking motion that eventually caused the filament to cross over. I use the supplied filament trays that come with the MMU2S.

The solution for me was to add a festo feed through connector to the tray and adding a 5cm loop between the tray and buffer. There is still some rocking, but it is not enough to loosen the filament on the backlash.

Phil 

RE: Filamentgrinding issue probably caused during unloading

A list of my mods so far:

• Universal auto-rewind with stiff spring: https://www.thingiverse.com/thing:3338467
  I have my own custom spool stand for that though and for filament guid I merely constructed to guides on both sides of the spool to prevent rewinding besides the spool.
• PTFE tube rear holder: https://www.prusaprinters.org/prints/6605-prusa-mmu2-ptfe-holder-m10-passthrough-adapter
• Selector with magnet: https://www.thingiverse.com/thing:4104419/comments
• Modified IR sensor triger (Extruder idler), I printed several versions with longer ticks that are triggering the sensor (in 0.4 mm steps) and chose the one with the best reliability.
• Planned: replacing 2 mm ID PTFE tube between MMU and Extruder with a 2.5 mm ID PTFE tube.

  I know that those are not strictly necessary, if your out of the box MMU2s works great for you, perfect. If not those are things which can make it more robust I suppose. Unless the issue is a defictive part like the barrel of course.

RE: Filamentgrinding issue probably caused during unloading

A small update: Tubing is still the original but the MMU2s is now starting to work fine, finally.

My 5 colour benchy printed without a single failure. If it stays that way, the MMU is starting to make fun 🙂