Originally Posted by
asammons
True, but the ball screw does not have the type of irregularities you are referring to at that short of a distance (maximum deviation is 0.003 over 12" of linear motion, not over 0.5" separating the two ball nuts).
I'm with you A.S. If the MAX deviation is .003" over 12 inches, the most you'll ever have to deal with in .5" is .000125. That's 125 MILLIONTHS guys. That small piece of aluminum isn't going to be stiff enough to keep that from happening. Especially through a couple small fasteners! Also, as A.S. states, the nut can rotate somewhat since the aluminum strap isn't that great in torsion. That 125 millionths of an inch translates into 1/1600 of a turn - less than a quarter of a degree (which is less than .002" on the circumference of the nut). And this is all WORST CASE, it's likely to be about half that.
The entire system isn't stiff enough to be the problem you are theorizing. Remember EVERYTHING is a spring, some are just stiffer than others.
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." Antoine de Saint-Exupery (1900 - 1944)