I’m rebuilding a small knee mill right now and was wondering if I should considering replacing the old Acme screw with a ball screw leadscrew. Given that this is a small mill with a 24x6” table would the ball screws offer any significant advantages over the Acme screws? This mill will stay a manual mill, no plans on converting it in the future.

Leave it ACME. Ball screws back drive, and need a significant resistance, like motor torque or a friction brake.