Better thumb z-crank

by whosawhatsis, published

Better thumb z-crank by whosawhatsis Jan 31, 2011
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I liked ssd's thumb crank, but it was rough around the edges (literally and figuratively) and just didn't feel quite right. My finger kept slipping off of it when it turned, and I realized that it needed a narrower shaft to allow the finger to get some purchase, and I wanted to figure out how to make those sweet curved contours with rounded edges in OpenSCAD (hint: lots of toriods). This is the result. It works extremely well and feels disconcertingly good turning around the finger. Best of all, it's made in OpenSCAD, and is fully parametric.


The hole should be about .5mm smaller than the rod (the STL is sized for the makerbot M8 Z-rods), and should screw on tightly, self-threading as it goes. Like ssd's crank, it should be tight enough to not need a set screw, but if you've got screwy tolerances on your printer that make it too loose, you can always change the bore variable in the scad file.

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I like it, something useful. :-D

This really worked well for me and saves a lot of time in setting up the z-axis distance.

Nice little Z knob. Looks like a dog bone on the end ;)

Very nice! I've been using OpenSCAD a lot, but I did my version in blender specifically because I didn't want to figure out how to do the filets and splines in OpenSCAD. I wish there was a filet function or something... (or spline for that matter..)

It took a couple of days on the back burner before I realized how to do it. The concave corners were especially difficult, as it took a lot of square roots and arcsines to get the placement right, but it was soooooo worth it. You have to print one just to feel how smoothly it turns around the finger.