Chucks are modified for spring clamp, air open. Special hardened and ground 4140 top-jaws grip O.D. of drive shaft slip yokes. Jaws have excess material milled away to reduce centrifugal forces. A special hardened and ground alloy steel spline driver is mounted to chuck face for easy loading and driving of shaft as it spins to 3,500 RPM for balancing. • T.I.R. = 1/10,000. • Cycle time 60 sec.