MMU2S and extruder fighting each other
Just put together the MMU2S for my new i3 Mk3S, which had been printing fairly reliably for about a month before I upgraded to the MMU2S. Brand new firmware for both the printer and MMU as of this morning. I tried the buffer but quickly removed it because it introduced a ton of friction.
Here's what happens: I can "load filament" just fine, but when I "load to nozzle" it pushes the filament into the extruder where the hobbed pulley grabs it. The extruder motor then stops, holding firmly onto the filament. But the MMU then tries to pull the filament back, which strips the filament and clogs the pulley, until I get a fast red blink on the MMU and the LCD says "MMU needs user attention."
I've calibrated the IR sensor and the FINDA, they both test fine. Any thoughts?
RE: MMU2S and extruder fighting each other
It was the IR sensor. Weirdly when I tested it with a piece of filament it worked, but apparently it was barely on the edge of on/off so it was sort of intermittent.
Still a worrisome amount of friction in the PTFE so we'll see how the first multi print goes.
RE: MMU2S and extruder fighting each other
@joel-2
I realized that the IR PCB is 8 mm wide and the slot of the chimney is 8.5 mm wide.
I modified the original stl file (ir-sensor-holder-mmu2s) adding a 0,4x1 mm spacer on the side opposite to the opening of the shutter (the red portion of the picture. Printed the part in in black PETG, smoothly sand the top to allow the cover to hold in place the IR PCB. In a different way is what you did.
RE: MMU2S and extruder fighting each other
It was the IR sensor. Weirdly when I tested it with a piece of filament it worked, but apparently it was barely on the edge of on/off so it was sort of intermittent.
Still a worrisome amount of friction in the PTFE so we'll see how the first multi print goes.
It quite often comes down to that problem. Get it right and everything works out.
As to your friction worries though; check my reply to this problem https://forum.prusa3d.com/forum/original-prusa-i3-mmu2s-mmu2-assembly-and-first-prints-troubleshooting/first-layer-calibration-mmu2s-constantly-loads-and-unloads-the-filament-to-the-nozzle/#post-361246
RE: MMU2S and extruder fighting each other
How does your buffer introduce a ton of friction? Mine doesn't really add much friction at all, its the ptfe tubes in between that does that and its not really problematic... I ask because I have seen this alot online, but haven't understood the problem, did you not remove the rubbery protective film from the plates prior to assembling? I found that you shouldn't really put in the screws holding the ptfe tubes much at all if you can avoid it as well...
RE: MMU2S and extruder fighting each other
@ejth
Generally it's the holes the PTFE tubes squeeze into. On the buffer side if you tighten the screws too hard it pinches them, if you don't tighten them enough the tube keeps popping out. On the MMU body side it's the clamping mechanism, and the terminating holes. All of these adds a ton of friction. All easily removed with a few cheap couplers and the mods people have suggested. As you say - it's not the PTFE tubes, but the fact that they're deformed.
RE: MMU2S and extruder fighting each other
@stewartr
I saw the mods, but honestly I think its over kill because you just have to use very little tension and thats all. I will confess that I have owned and operated the MMU2 only for a week or so, but it works as advertised without the mods, if you just use very slight tension, what I did was actually use no tension at all, and if the tubes slipped I would give it half a turn and wait to see if it was enough.