The Production of High Rotational Speed Available to Purchase

Small steel rotors have been suspended by an axial magnetic suspension using inductance control to effect vertical stabilization. They have been spun in vacuum by means of a rotating magnetic field having a frequency of the order of 100 kilocycles. Rod rotors tended to precess in the absence of horizontal damping. This was remedied by placing a copper block just above the upper end of the rod. A tapered length of drill rod ⅞″ long (max. diam. $316′′$⁠) reached 36,000 r.p.s. before bending double due to the effect of centrifugal force. Steel balls have the advantage of no precession; however, on starting to spin they soon built up a circular orbital motion of increasing amplitude. A damping needle situated outside the vacuum system and immersed in oil was found to eliminate this motion satisfactorily. A $332′′$ diam. ball has been spun to 110,000 r.p.s. This corresponds to a centripetal acceleration at the periphery of 58×10⁶ gravity. The rate of free deceleration at 106,000 r.p.s. was about 1 percent per hour. Rotational speed was measured by observing the rotor in stroboscopic light whose frequency could be matched with the speed of the rotor.