I am about to start a CNC conversion of a HF mill/drill and have some important questions about my ball screws.

I have liberated some 5/8" x .200 ball screws from some equipment I acquired several years ago. The problem is that the double angular contact bearing setup on one of the ball screws is a bit small for my taste (they turned the screw down a bit more than I'd prefer). Anyhow the end result is that I'd have to mount my pulleys on a shaft diameter of only .250" and I'm concerned about shearing off a 1/4" shaft at some point.

The question is, if I mount the screw the other direction and drive it from the other end will I run into screw flexing problems? The way I see it is that any axial thrust is between the thrust bearings and the ballnut, and any radial torque is between the pulley and the ball nut, same distances regardless just different layout, am I correct?

I have one axis with the pulley on the angular bearing end and the other is on the radial bearing end.

No problem from either one of them! Remember, the pulley is transmitting only radial force. so the lead screw doesn't care which end it comes from. If your using a belt drive, the minimal thermal expansion will not make any difference to the accuracy of the machine.

Thats basically what I figured , but I have yet to see any pictures of peoples projects done that way and was wondering if I was missing something.
I will be using a belt drive for sure so the pulley end of the screw will only have a slight radial load, no problem.