A keyway ballnut screw is just that: a screw which runs on ball bearings.
The screw and nut have matching helical grooves or races, and the
ball bearings recirculate in these races. There is no physical contact
between the screw and the nut. As the screw or nut rotates, and
the rolling balls reach the trailing end of the nut, they are
deflected or guided from this “pitch” contact by means
of a return tube and returned to the leading end
of the circuit. There, the cycle resumes and
the balls recirculate continuously.
