Quote Originally Posted by V8kid View Post
Are there any rules of thumb relating to acceptable ballscrew lengths without BF bearings? I guess its a function of the ballscrew diameter and the applied load?

I'm using 20mm diameter and 266mm length with a NEMA 34 1700ozin stepper with a 2:1 drive reduction.

Cheers!
What's been said is all good advice, but for a bit more insight look up "critical speed calculator" or something like that. There are a number of sites around which give graphs and so on which give an estimate of the critical speed for leadscrews/ballscrews based on diameter, length, and end support (fixed/unsupported, fixed/floating, fixed/fixed, etc). Critical speed is the maximum speed before whip in the screw becomes evident/becomes unusable.