Patent ID: 8753016

Claim:
A spindle unit of a machine tool, the spindle unit comprising: a rolling bearing including an outer ring having an outer ring raceway groove on an inner peripheral surface, an inner ring having an inner ring raceway groove on an outer peripheral surface, and a plurality of balls provided rollably between the outer ring raceway groove and the inner ring raceway groove and having a contact angle of more than zero degrees, the inner ring being fitted onto a spindle of the machine tool whereby the spindle is borne rotatably in a housing; and a grease supply system for supplying a grease to an inside of the rolling bearing during a rotation of the spindle; wherein the grease supply system supplies the grease such that a supply amount of the grease in one shot is set to 0.004 cc to 0.1 cc to prevent a temperature pulsation of the rolling bearing, the temperature pulsation being a transitory increase of a temperature of the rolling bearing, wherein the grease supply system contains a supply hole provided in the outer ring, the supply hole extending in a radial direction of the rolling bearing and having a diameter of 0.1 mm to 5 mm, wherein the outer ring raceway groove comprises a contact portion that contacts the balls, a maximum diameter portion having a maximum diameter of the outer ring raceway groove in the radial direction, and a reduced diameter portion having a smaller diameter than the maximum diameter portion, the reduced diameter portion being formed on a side opposite to the contact portion with respect to the maximum diameter portion in an axial direction of the rolling bearing, and wherein the supply hole is opened at a location on a portion of the inner peripheral surface of the outer ring other than the outer ring raceway groove such that an outlet of the supply hole overlaps a portion of the plurality of balls in the radial direction of the rolling bearing, said location being opposite to the contact portion with respect to the maximum diameter portion in the axial direction, and said location being adjacent to the reduced diameter portion of the outer ring raceway groove.