I worked this up for myself a couple of months ago and never released it because I didn't want to muddy up the waters with the adjusted belt path. When Prusa released the MK3S with the R4 Y-Idler I compared mine to theirs and saw that I was only 2/10mm different from what they have. Being that I'm happy with my belt path I have decided to leave well enough alone, but also thought others might want this version. If you use this version you really should change the Y-Belt holder as well as it too has been adjusted to maintain a horizontal belt path. I also posted the same tensioner with the idler pulley 2mm higher, original Prusa location. See PDF for more detail.

Items you'll need for this:

(1) Gates 20T idler with a 5mm bore
(1) 4.95'ish mm diameter shaft at 24mm long (opening is 24.5mm so 24mm works just fine
(2) M3 x 20mm socket head cap screws (1) for the pivot and (1) for the tensioner
(2) M3 x 8mm socket head cap screws to mount tensioner to the frame
(4) M3 hex nuts, can use flats or Nylock but I see no reason to use Nylock nuts

I included (2) .4mm washers to center the idler, not necessary but I prefer them.

Note the nuts are a tight fit, I do this to keep them from falling out but be prepared to put some effort into seating them, except for the tensioning nut slot.

Print without supports and as oriented in the files, except the washers need to be properly oriented

I printed on standard Prusa settings, 2 perimeters, 20% infill and all works fine, feel free to print as you see fit.

Print instructions

Unassociated tags: Prusa MK3
Category: 3D Printer Parts