Prusa MK3 Adjustable Y belt Tensioner

thingiverse

An adjustable tension-er for the y-belt was crafted to replace the oem setup of using idler support attachment bolts for tensioning, which allowed the belt to wander a lot and bear hard against one side or the other of the pulley. To achieve stability, I tightened up the mounting bolts to align the support, necessitating a scheme to allow tension adjustment. This required a pivot pin, which I fashioned from a piece of 2mm carbon rod that was readily available. Piano wire (2mm or 3/32") could be used as an alternative. The thru holes for the pivot pin are @ 2mm in the .stl files, allowing room to drill them out to a reasonable size. I sized the holes in the bracket part to provide a light press on the pin and opened the hole in the hinge part to allow free movement (~0.05-0.1mm ~ 0.002 - 0.004" larger than the pin). A 3mm, 16-18mm long tension bolt is used, which can be longer if desired. This iteration employs the stock thru bolt and pulley, so caution should be exercised to avoid over-tightening the thru bolt during assembly. Two versions are available: one with the pulley located at the oem height in z and a lowered (1.25mm) design that utilizes RHDreamboxes y belt holder, which levels the belt path. Retainer nuts should be installed before pressing the hinge pin in place. To locate the bearing at the c/l of the bracket, I incorporated a detail using aluminum spacers as crush tubes to allow the thru bolt to be tightened up against the center bearing race. If there is interest, this feature will be uploaded. It requires well-made tubes. A 3mm drill was used to clean out the slot on the tension bolt support and a flat washer was installed under the head of the bolt. The support-to-bolt-head surface is cylindrical to compensate for tension bolt angularity.