Better thumb z-crank

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.