Easy Reliable Coupler
I have finally come up with a solution for an easy reliable coupler you can make out of plastic. The attached STL file is a 3/32 to 1/4 coupler. It is 1/2" long, and 3/4" diameter. It uses 6 #4 nuts that are forced fit into the slots around the hole. This is so that the set screw does not strip out the plastic. 6 #4 X 3/8" set screws go through these nuts and hold the shaft in place. They can be adjusted so that both shafts are perfectly concentric. I have tugged on the shafts, and the set screws hold them very tight. I could not pull them out of the coupler. This should work for all of the motors on the printer. I think it can be reprapped, so try it out. It can be adapted easily for other bore sizes, so if you want a different size, just tell me.
Also, pliers are needed to force the nuts into the slots.