At Alexey Volegov's hands a rotating metal planetary chevron gear, a non-separable system that can only be obtained by 3D printing. Printed at UrFU laboratory. Disclaimer: AAAS and EurekAlert!

In those mechanisms, a high-torque, low backlash gearbox might be just the thing, and a 3D printable split planetary harmonic ... as we saw in this 3D-printed strain wave gear.