Motor/Leadscrew Couplers

I'm kind of a newbie at this and I'm trying to interface the Frog to my
lathe. The end of the leadscrew on my lathe has an external M8 x 1.25
thread, about 8mm long. The stepper motor is a nema 23 with a 0.250"
diameter shaft. I was wondering if the group members had suggestions on a
good coupler design. I machined a "hard" coupler out of aluminum threaded
one side to screw on the leadscrew and reamed on the other side for the
shaft. Each side has a couple of set screws to hold it in place. I was told
that you don't want to use a hard coupler and I kind of believe it -- any
slight misalignment of the motor causes the friction to go through the roof.

Any suggestion would be greatly appreciated!

Thanks,
Kory