will this 4th axis work

[Jonathan]

And this will give you a perspective on sizes. Size 11, size 14 and size 25

Lightweight ;), here's a size 50:



I had two of these sitting in my shed for 5-6 years - like Robin I found out about them and immediately decided I must have two. Then I got very sidetracked, so I sold one recently and held on to the other. I think I'm more interested now in coaxing a high torque motor into a direct drive axis, as the cost of encoders is decreasing. Seems more elegant.

One interesting point with harmonic drives is that although they don't exhibit backlash (if well made), they still do have some hysteresis. Still, beats buying a chuck driven from a stepper motor via a rubber band.