A double nut preloaded ball screw changes a ball contact points from three to two while the motion direction change. The transient friction torque after motion direction change is less than that in the steady state and cause contouring error of circular interpolation. Oversize ball nut preloaded ball screw don't change the ball contact points, and for this reason, friction torque almost changeless at the motion direction change. As a result of using the oversize ball nut preloaded ball screw for a machine tool, the contouring error by the ball contact points change delete.
