Abstract: A spindle of a machine center is held in a spindle sleeve directly straightly driven by a servo-controlled motor aligned with the spindle axis for preventing any bending or twisting caused to the rotating spindle during cutting operation and having a plurality of longitudinal cooling passages parallelly longitudinally formed in the spindle sleeve proximate to an upper and a lower bearings disposed around the spindle for enhancing the cooling effect of the running spindle, and having a direct application of cooling oil mist or gas stream into the bearing systems of the spindle to greatly minimize any frictional heat or temperature raise caused from the running spindle to prevent a thermal expansion influencing the processing precision of the cutting operation.