Improved MMU3 idler (updated)

I love my MMU3, but too often when loading the filament to the MMU it misses the output tube and sticks out between the idler and selector (see picture).

This mod adds raised ridges to the idler ensuring filament remains on the right path when loading filament to the MMU pulley body.

It is assembled in the same way as the original MMU3, except that the bearings must be inserted from the back side of the idler. 

UPDATE (20250318)

Thank you to feedback from @leks_2435828 and @RonnyL_2916864, I have adjusted the tolerances to ensure the idler does not unintentionally contact the grub screws or or pulley body.

Idler Body

• Moved right bearing surface to align idler in the idler body.
• Added bearing surfaces to pulley body mating surface to ensure proper alignment with the pulley body.
• Adjusted grooves to match updated idler.

Idler

• Reduced overall diameter to ensure it doesn't contact pulley body.
• Adjusted filament guide protrusions to better clear the grub screws. 
• Reduced material at stepper motor end to better clear pulley body bearing.

Assembly is as per the Prusa instructions (https://help.prusa3d.com/guide/4-idler-body-assembly_328304). Note: 

• When installing the idler in the idler body ensure that that the ridges on the idler are centered in the grooves on the idler body before tightening the coupler grub screw (step 18 in the Prusa assembly manual).
• After the idler body assembly is complete, ensure the idler moves freely between stops. 

UPDATE (20250322)

Thank you to feedback from @Hundehirn_354205. I have added 0.5mm to  the right bearing surface to ensure alignment of idler in the idler body.

UPDATE (20250323)

Thank you to feedback from @leks_2435828 and @NATEwismer_716891. I removed 0.9 mm from the idler to clear the pulley body bearing.

UPDATE (20250624)

I have uploaded an improved pulley body model that helped me reduce filament resistance in my MMU. I have not had time to fully test this beyond a couple of successful prints so please use at your own risk. Feedback is appreciated but I am not sure how much time I have to keep working this.

Based on the R3 version. Added grooves to the idler and modified idler body to fit.