@Ryan_Carlyle wrote this comment on Reddit and I think it deserves to be memorialized. I was one of those who didn’t understand why not ball screws for X & Y but this totally makes sense.
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In the case of ballscrews, it’s not just the increased angular momentum of the screw that you have to worry about, though I agree that that’s a great reason not to use them. There’s also the increased linear momentum of the ball nut, which is going to have have a lot more mass than a belt clamp, or even the nuts used by leadscrews. Ball nuts are larger and mostly steel, unlike lead nuts, which are usually smaller pieces of brass or plastic, sometimes with a spring for anti-backlash purposes.
You also have lots of small points of contact inside the ball nut, which will concentrate pressure during the rapid starts/stops, which is not good for them. The same is true, of course, of the bearings holding the screw in place (which should really be bidirectional thrust bearings, not just the radial bearings we usually use), because they need to handle the same reaction force. If you’re relying on the bearings in the motor for this, they’ll be much harder to replace if you damage them.
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