The hardest part to make for a harmonic drive is the actual flex gear and splines. I goofed around making cup style flex gears but those seem to fatigue really quickly. Someone showed me the 2 spline style that gets rid of the cup. This seems to be a very well suited for 3d printing.

I created a 200 and 202 spline and a 200 tooth flex gear. This gives me 100:1 gear reduction. (or 101:1 depending on where the stationary spline is in the gear train)

Using a GM wheel bearing for the high torque end of the rotary axis works well. (it can be popped part and the inner race ground to increase pre-load.)

PLA is not a good choice in this application. It seems to break up pretty quickly (hours of use) PETG is a much better choice. I have been testing with a set of printed PETG gears and have not broken them yet (even when torque testing)

I have not done a bunch of actual machining yet - but am happy so far with its performance.