From another thread I started looking at the MSC catalog online. I wondered if anyone has used alloy steel oil finished or chrome moly zinc plated 3/4-10 rod to drive there machine. I would think that it would help the whipping problem at higher RPM and smooth the acceleration by adding some mass to get spinning while providing a longer pitch for speed.

http://www1.mscdirect.com/CGI/NNSRIT?PMAKA=05365705&PMCTLG=00

You'll need much bigger motors if you use 3/4" screws vs 1/2" screws. The extra mass is much harder to spin.