Improved Prusa Mk3S MMU2S filament sensor mount by 01chevyguy

Last crawled date: 3 years, 3 months ago

This is an improved mount for the Prusa Mk3S MMU2S extruder filament sensor that allows for more precise adjustment. It replaces the ir-sensor-holder-mmu2s, the fs-cover-mmu2s, and the adapter-printer-mmu2s with only two parts.
I struggled with getting the filament sensor adjusted to work reliably with both PLA and TPU filament. With the original design, you loosen a screw and nudge the sensor mount to adjust but there is no way to make fine and controlled adjustments. This improved design uses a setscrew to precisely adjust the filament sensor position and has greatly improved MMU2 loading reliability for me. Hope it works for you too.
To create the set screw, I used a square nut (M3nS, spare that came with the Prusa kit) drilled out to let a 2.5mm allen key pass through smoothly, and a M3x18 screw (also spare with kit). After printing the two parts, assemble them and insert the screw, then insert the nut from underneath to retain the screw. Now by inserting an allen key through the nut, you can finely adjust the position of the filament sensor by turning the allen screw.
I found that in order to remove the original fs-adapter from the extruder, I had to loosen, but not completely disassemble, the two halves of the extruder body. Once loosened, the fs-adapter came out easily and I inserted the new assembled part and then retightened all the extruder body screws. Finally, insert the screw in the top of the fs-cover, but do not tighten.
Adjust the filament sensor following the procedure in the Prusa manual, except move the sensor precisely by inserting an allen key through the drilled out nut and turning the screw. Once the adjustment is correct, tighten the fs-cover mounting screw on top.
Edit: Added photographs of assembly.