Improved X and Y Idler Mounts for Prusa MK2s - MK2.5s

thingiverse

The wobbly X and Y idlers on my Prusa MK2s were driving me crazy, even though prints came out OK. The wobble originates at the 3mm bolts that act as axles for the idler pulleys... First, as the bolts are threaded and not precisely sized there is looseness between the inner race of the bearings and the bolts. Worse, one cannot tighten the bolts, as it will crush and deform the non-reinforced plastic mounts. Of course this allows the axle bolts to wobble in the plastic as well! My solution here is to use idler pulleys with a 5mm bore, running on hollow 5mm O.D. stainless steel tubing as axles. The Idler holders are modified with 4.9mm holes and are intended to be filed or reamed to a tight fit on the tubing. The tubing should be cut just short of the depth of the hole, maybe 0.1-0.2mm, to allow the plastic to be crushed very slightly. As the 3mm bolts now bear primarily against the steel tubing, they can be tightened fully without distorting the plastic excessively, so self-locking nuts are no longer needed. On my build I used Gates Powergrip 20T toothed idlers, which are slightly wider than the standard Prusa idlers. The Y axis idler holder accommodates the wider pulley but the X axis holder does not. The cavity for the pulley can be widened is PrusaSlicr using modifiers, so I included the .3mf file for the X axis Idler Holder with the modifier already set. This build requires hand fitting of the parts! As mentioned, the holes are intentionally slightly small to be reamed to size. The steel tubing must be cut to precise length and the steel tubing may well be oversized in diameter, necessitating chucking it into a power drill and sanding it down to fit the bearings tightly, preferably before cutting it to length. When it is all done, the idler pulley wobble is GONE! Does it improve prints? Maybe slightly. The printer seems slightly quieter, which was an unexpected bonus. Happy Printing!