Prusa Mk3s extruder using an indirect Mk3 filament sensor.

thingiverse

Fully tested now, I've put my hardest PLA and softest TPU through their paces, and both fed through quite easily. First passes may be a bit rough due to layering, but a quick run of filament should smooth things out. This is a reworked version of the Prusa Mk3s extruder that uses an old filament sensor with a proxy bearing for indirect sensing. It shares the same bearing and design concept as my earlier mod, which can be found here: https://www.thingiverse.com/thing:3223513. The new design is easier to print because the bearing container has been miniaturized and can be reprinted easily if you need to tweak tolerances. You'll need an M3 x 6mm screw with a low-profile head to secure the bearing, an M3 x 8mm screw for the filament sensor, and standard Prusa 10 and 12mm screws. The bearing can be held in place by any M3 screw less than 9.3mm long, with a head no thicker than 2mm (aiming for 1.6mm). An M3 x 6mm screw is ideal. To assemble the extruder, screw the sensor to its carrier and attach it to the extruder body. Then, drop the bearing into the carrier (clear out any debris first) and secure it with a 3mm screw. You'll need to reprint parts if you want to use the newer on/off sensor in a standard Mk3s configuration, but these parts should work fine with the MMU2s. I've included three top caps: a standard one, an M10 reverse bowden design based on this https://www.thingiverse.com/thing:3425397 by Wardy89, and a rivnut-based coupler design. Update 18/2/19: I've shrunk the lower heatsink hole to match R3 extruder dimensions, reduced the E3D clamp size to fit R3 extruder requirements, and improved cable routing for the sensor and MMU. Some clearances around the filament sensor have also been enhanced. Update 22/2/19: I've re-added a window into the extruder on the left side so I can see the gears, loosened the filament sensor tolerances, and modified the top plate with coupler to work with my opening idler door mod. Update 02/3/19: I've added nut pockets for three of the four screws of the Noctua fan. There's space for a brass insert but not for a nut in the last corner. A small key tab has also been added that links the floating end of the front cover plate to the extruder body by the Pinda mount, which reinforces that area as it's exposed to significant radiant heat near the hotend.