Improved Promega CoreXY Belt Tensioner

thingiverse

This is a remix of supinemonkey's excellent Promega belt tensioner mod that improves upon his design. The improvements are: 1. The horizontal mounting hole on the knob bracket has been reduced to an M4 thread due to the holes in the Promega frame being too small for an M5 screw. 2. The NEMA motor spacer has been flattened to accommodate a 10mm threaded standoff in order to reduce or eliminate the distance the motor pinion has to be moved up the shaft. The new spacer places the motor within about 0.5mm of the factory position. The knob remains the same as in the original design, but I've included it here for completeness. A few items from the original design description need to be cleared up: a. The screw for attaching the knob bracket to the motor mount must have an M5 thread. Both the motor mount and the knob bracket have M5 threads cut/printed into them. b. The M5 screw length on the right side (as viewed from the front of the printer) needs to take into account the extra thickness of the rear cable chain bracket. I used an M5x20mm screw with <a href=https://www.thingiverse.com/thing:3407076>my remixed version of the latest M3D bracket design</a>, which is fine for the official M3D version as well. c. The threaded standoffs must have a 4.5mm outer measurement. I mention this because some M3 standoffs have a 6mm outer dimension. I found a cheap source for standoffs <a href=https://www.amazon.com/gp/product/B073XP7MZ6/>on Amazon.com</a> (ignore the 16mm reference in the description). You may need to cut about 2mm off the screw end to get them to screw in all the way.