Thanks Tweakie. You've been very kind with all responses. Makes sense - I was wondering about any extra stress on the motors if the couplings were not spot on. Perhaps the low-rent solution of gas lines and hose clamps is easier on the bearings in the steppers. I like the look of the coupling nut though. What would be your guess on the reduced lifespan of a stepper if the coupler was a little off? I'm sure there is a wide variable range there though - the degree of off-ness, the quality of the motor, the speed at which it's run...
Anyhow, I'm learning a lot as I putter along here. When I look back on past projects over the years, the first prototypes are almost always greatly inferior to subsequent builds. With that said, I've spent a lot of time on this one, and when it's complete I'll pretty it up a bit with some stain, varnish, and assorted shiny bits.
Thanks again,
Zig