Without these modifications I had a number of problems with my MMU2:
- regularly could not feed filament into the selector. Successful tool changes were very rare... in fact I can't think of more than 3 or 4 fully interaction free tool changes before I installed this mod.
- the blade holder didn't actually HOLD the blade. I eventually had to disassemble the entire selector mechanism because the blade had wedged into the part it slides over and dug in so bad it prevented the selector from moving in either direction. about 4mm of the point of the blade was inserted between layers of the prusa printed part.
With these modifications I still occasionally have issues:
- unable to get filament to properly lift the ball under the FINDA some times. I can hear that it made it in that far, just the shape of the tip isn't actually engaging correctly.
- unable to get filament that is slightly curved (such as fresh off a spool) to initially load some times, it hits the wall NEXT to the opening after the pressure roller. (I think the same approach taken in this mod, one part earlier, will help solve that.
- occasionally the filament does not withdraw as far as the printer thinks it did after triggering the FINDA... this results in the blade actually slicing through filament... often this then results in the selector not properly aligning to the filament path it's supposed to be on. (fix is to manually rotate the selector worm gear to move it the last little bit... assuming you can tell which one it thinks it needs to be at!)
Since making this modification, I've made hundreds of successful tool changes, fully automated.
(seen also in this build shot: https://www.thingiverse.com/thing:3338467)
I ended up having to put a raft around the selector itself because the small foot that forms the clamp for the FINDA kept having adhesion issues. The other parts all printed fine without it.
Oh, and I printed with "clear" HTPLA in hopes of being better able to see where the filament is when debugging issues. With very dark filaments, or with a bright light, this is possible... but it's nowhere near as useful as I hoped.