Improved Promega CoreXY Belt Tensioner

thingiverse

This is a remix of supinemonkey's excellent Promega belt tensioner mod that builds upon his design. The improvements are: 1. The horizontal mounting hole on the knob bracket has been downsized to an M4 thread because the holes in the Promega frame were too small for an M5 screw. 2. The NEMA motor spacer has been flattened to fit a 10mm threaded standoff, reducing or eliminating the distance the motor pinion must move up the shaft. This new spacer positions the motor about 0.5mm from its original position. The knob remains unchanged like in the original design, but I've included it here for clarity. A few points from the original design description need to be clarified: a. The screw attaching the knob bracket to the motor mount must have an M5 thread. Both the motor mount and the knob bracket feature M5 threads cut or printed into them. b. The M5 screw length on the right side (as seen from the front of the printer) needs to take account of the extra thickness of the rear cable chain bracket. I used a 20mm long M5 screw with my remixed version of the latest M3D bracket design, which works fine for both the official M3D and this remix. c. The threaded standoffs must have an outer measurement of 4.5mm. Some M3 standoffs have a 6mm outer dimension. I found a cheap source for standoffs on Amazon.com (ignore the 16mm reference in the description). You may need to trim about 2mm from the screw end to get them to screw in fully.