Shaft Coupling with Spider 3" (Public Domain)

thingiverse

This style of shaft coupling can run you $150 apiece for each individual coupling, excluding the cost of the bronze or rubber spider. You can now make your own. The spider absorbs any misorientation of the shaft that could cause a bending-moment in the couplings; it will fail instead of the coupling and can simply be replaced, but with good alignment the coupling will last for many years. This coupling is often used to transmit significant force as well. It was designed for a 1.5-inch shaft, but you could edit the shaft diameter to account for many combinations of shafts, with say, a 2-inch maximum. Ideal material is plain carbon steel for the couplings and bronze for the spider. This design can be machined or 3D printed; its teeth are designed to be millable with a 1-inch endmill or smaller. There is a keyway in each coupling; it's recommended that you use spring-steel as your key. To hold the shaft in place is a 3/8-16 threaded hole, and you can use a set-screw. Enjoy! I designed this using Solidworks.