I think something like this made out of aluminum 6061 would make a really good flexible coupler what do you think? My thinking on why they could use a good replacement is this...

Nylon tubes do a terrific job at low speed allowing for slight misalignments as they require only a small amount of torque to do their job but at 600 rpm thats still a "small amount times 600" which can be HUGE especially considering that the available torque from a stepper is falling off fast. Even a tiny improvement in efficiency would have a good effect on the top speed.

FYI on eBay the 1-1/8 round stock you can buy is 24" long and $14.50 or 48" long and $21.50. The couplers as designed are 1.5" long and by allowing 1/4" extra stock for finishing (less if you have a good saw) you would get enough couplers for 4 TAIGs from 24 inches.

This may be my first project for the TAIG as it kills me knowing the TAIG can move the spindle assembly UP at 46+ inches per minute with ease but only if I am holding the motor in place. As soon as I tighten the screws to hold the stepper in place it doesn't even come close to a speed of 46.

High resistance to torsion and Low resistance to slight misalignment would be the result from this?

Hmmmm....if you believe it's an alignment problem....then correct the alignment....apparently when you tighten the motor down it's being torqued out of alignment....so concentrate on that.

The lead screw has .0015 runout according to my dial test indicator I believe that is where the alignment problem is. Isn't .0015 ALOT?? I have the stylus perpendicular to the direction of movement so it should be a fairly accurate measurment.

The lead screw has .0015 runout according to my dial test indicator I believe that is where the alignment problem is. Isn't .0015 ALOT?? I have the stylus perpendicular to the direction of movement so it should be a fairly accurate measurment.

Where is the runout? On the end of the screw where it's threaded for the nut or the smooth part that the coupling seats in. Part of that is probably the fact that you haven't tightened the coupling nut which governs the load on the leadscrew bearing.

I am going to have to recheck the runout. I had the nut and coupler piece off the screw when I checked for runout on the smooth part of the shaft and I'm not certain if it could have been loose.