Patent ID: 7690873

Claim:
A spindle apparatus comprising: an outer cylinder having a stator; a rotatable rotating shaft having a rotor; a front side bearing having an outer ring fixed to a front housing and an inner ring fitted over one end of the rotating shaft; a bearing sleeve disposed on another end side of the rotating shaft and fitted in the outer cylinder so as to be movable in an axial direction of the rotating shaft; a pair of rear side bearings having an inner ring fitted over the other end of the rotating shaft and an outer ring fixed to the bearing sleeve to rotatably support the rotating shaft in cooperation with the front side bearing and wherein the diameter becomes smaller in the order of an inner peripheral diameter of the outer cylinder, an inside diameter of the stator, and an outside diameter of the bearing sleeve, wherein a sub-assembly made up of the front housing, the rotating shaft, and the bearing sleeve is withdrawable from the outer cylinder, wherein a radius of a rotating part in an arbitrary section located rearwardly of the bearing sleeve is smaller than a minimum radius of a non-rotating part between a rear end of the bearing sleeve and the section, wherein the bearing sleeve is fitted in a sleeve housing, wherein an outside diameter of the bearing sleeve is clearance-fitted with respect to an inside diameter of the sleeve housing; wherein the pair of rear side bearings constitute a back-to-back arrangement angular contact ball bearing with fixed-position preload; and wherein a ratio between a fitting length of the bearing sleeve and the sleeve housing, and an outside diameter of the bearing sleeve is set within a range of fitting length to outside diameter equal to between 0.45 and 0.8.