Y belt tensioner with standard M3 screw axle

prusaprinters

<p>Replacement for the Prusa Mk3(S/S+) y-belt idler, to allow easier adjustment of the belt tension.</p><p>Boogie improved on his original design of a y-belt tensioner by requiring only 2 screws for tightening but for some reason replaced the M3 screw that is used by the Prusa stock idler with a cylindrical pin. Which of course wasn't in my toolbox, so after some quality time with Fusion 360 I had remixed boogie's design to use a standard M3x20 screw instead, similar to the M3x18 screw used in the original idler.</p><h4>Parts required</h4><ul><li>2x M3x10 screw (from original idler)</li><li>3x M3 hex nut</li><li>2x M3 nyloc hex nut</li><li>3x M3x20 screws (boogie suggests M3x18 screws as tighteners but I found the M3x20 to give more range)</li></ul><h4>Print instructions</h4><p>PETG. 3 perimeters, 15-20% gyroid infill, 0.2mm layer height. No supports.&nbsp;</p><h4>Assembly</h4><p>This is assuming you're replacing the original idler. For “orange” and “black” please see photo.</p><ol><li>Insert 1 hex nut in orange part. In case you can't press the nuts in: Take M3 screw, thread it from the opposite side of the printed part, as you tighten the screw, it will pull the nut in.</li><li>Insert 2 hex nuts into the back side (with the “legs”) and 2 nyloc nuts into the front side of the black part.</li><li>Unscrew the four screws that hold the LCD display in place and put it aside. Keep screws in place for late re-assembly.</li><li>Unscrew the 2 M3x10 screws that hold the idler and set aside for reuse.</li><li>Unscrew the M3x18 screw that secures the bearing in the idler. Remove bearing. Screw and nyloc nut are no longer needed.</li><li>Hold the orange part with the little hole downward and the hex nut facing left.</li><li>Push the belt back over the bearing (without twisting it) and insert the bearing into the orange part.</li><li>Secure it with an M3x20 screw. Don't tighten too much, the idler needs to be able to spin freely.</li><li>Insert the orange part into the black part (with the little hole facing down and the legs away from you). Insert 2 M3x20 screws, tighten them into the nyloc nuts, then unwind until they just stay in place.</li><li>Attach the black part to the frame with the 2 original M3x10 nuts.</li><li>Reattach the LCD display.</li><li>Use the <a href="https://www.printables.com/model/46639">Prusa's “tension meter”</a> to adjust proper tension, by tightening the 2 M3x20 screws that go through the tensioner equally.</li></ol>