I made this shaft coupler to connect a NEMA-23 stepper motor to a ball screw drive that previously had a NEMA-34 servo motor.  It was designed to fit the motor mount that was part of the screw drive, but all dimensions are easily changed in DesignSpark Mechanical to fit any size shaft and any overall length and diameter.I sliced in Cura and used the "everywhere" support option.  I printed at 50% infill, 0.2mm layers.  After the print finishes you will have to spend a little time breaking the support material out of the spiral slots, but it isn't too hard if you use a scraper or knife.  Try not to cut your hands in the process!