Harmonic Drive

thingiverse

Print the rotor and the casing out of a hard plastic, and the spline cup out of a flexible material that can be easily shaped. It's crucial to apply lubrication to all moving parts - I used a silicone oil but mineral oil should also work well. A small amount is sufficient, as excessive lubricant can cause problems. I haven't tried PTFE yet, but it might prove effective too. Make sure to avoid adding supports to the spline cup at any stage of printing.