The unidirectional bearing often operates at high speed and ultra-high speed in motorized spindle, so the centrifugal force has a great influence on the running state of the bearing. At high speed, the centrifugal force tends to move the ball outward, that is, a moves to A1 and B0 to B1. At this time, the contact angle of the inner ring will increase and the contact angle of the outer ring will decrease. As a result, the center of mass of the steel ball deviates from the rotating axis, resulting in gyroscopic moment.

The friction heat generated by sliding not only aggravates the temperature rise of bearing, but also leads to local annealing on the surface of steel ball, which increases the wear and burn degree. In order to overcome the influence of centrifugal force, one-way bearing always runs with preload in the spindle. Proper preload can make the contact angle of inner and outer rings consistent during operation, which can not only prolong the bearing life, but also improve the rigidity of bearing and spindle.

If the preload is too large, the bearing lubrication and heat dissipation conditions are poor, the bearing life is short and easy to burn or jam under the same service conditions, and the worse the high-speed performance is, the support rigidity of bearing and spindle will be greatly increased. If the preload is too small, the overall rigidity and bearing capacity of the spindle will decrease obviously.

If the preload value is not enough to overcome the influence of axial force and driving force on the spindle, the spindle will produce obvious vibration and the workpiece surface will appear obvious vibration marks. If the preload is not enough to restrain the gyroscopic torque, the spindle bearing will be heated rapidly due to "slipping" and obvious wear marks will be found on the surface of the steel ball.