Why is the Spacer Ball required then? Ball Screw is spiral structure unlike Bearing, so
retainer cannot be inserted between Balls. Because of this, Balls next to each other always
contact, so Balls scrape all the time. This phenomenon is one of the reason to deteriorate
the smooth movement (i.e. Torque ripple, hand-feeling). It is effective to install Spacer
Balls, which is slightly smaller than Load Balls to relieve this scrape. Spacer Balls play a
role of retainer between Load Balls and dissolve scrape of Balls. Installing Spacer Balls are
especially effective for oversized Ball Preload.
Therefore, for precision positioning machine, Spacer Balls are usually used to avoid
deteriorating smooth movement, even though Capacity and Rigidity decrease.