Gyroscopically stabilized spin cast machine

A machine for spin casting concave optical surfaces said machine having a concave spin casting mold and a gyro rotor which gyroscopically stabilizes a vertically positioned rotating shaft supported by lower and upper ball bearings, the lower bearings are preloaded by the weight of the rotor and shaft, the upper bearings are preloaded by a spring force which moves a preload collar upward and forces the inner ball bearing race and the ball bearings upward against the outer bearing race, the lower ball bearings positioned below the gyro rotor and the upper ball bearings positioned above the gyro rotor and below the concave spin casting mold, movement of the rotor shaft away from the intended vertical position is resisted by the gyroscopic force provided by the rotating gyro rotor, changes in the rotational speed of the rotating shaft are resisted by the inertia force provided by the rotating gyro rotor.