A simple knob for the top of the 5/16" all-thread on the Printrbot Simple beta. Since the printer doesn't have endstops, it's nice to be able to make fine adjustments to the printhead height.
Please note that as with many of the things designed for the original Printrbot Simple beta, this knob is not usable with the current production Simple, which now comes with Acme rod; instead, try http://www.thingiverse.com/thing:145804
This knob is generated by jridley's very nice OpenSCAD library for hex-head screw knobs: http://www.thingiverse.com/thing:11797 using these parameters:
screw_knob(26, 5, 20, 6, 3, 12, 0.4, 8.3, 13, 6);
I printed it (on the Printrbot Simple) with PLA, 3 perimeters, 40% infill. Clear the hole with a drill bit, knife or file, then press fit a 5/16" nut into the hex hollow. Thread a second nut onto the all-thread, and use it to lock the knob in place.
For anyone having problems slicing the knob, I've uploaded a gcode file based on the settings for our Simple. You can try printing as is and it ought to be fairly close, or you can tweak the start G-code to reflect your calibration numbers.You may also want to look at JohnSL's version here: http://www.thingiverse.com/thing:91438