COOLING STRUCTURE OF BUILT-IN MOTOR

PROBLEM TO BE SOLVED: To effectively cool a built-in motor incorporated into a machine tool, and simplify structure. SOLUTION: A main spindle 23 is provided at its one end with a grinding wheel 12, and consists of a heat pipe 31 filled with a heating medium therein. The main spindle 23 is rotatably supported to a housing 21 through a plurality of aquatic static pressure bearings 34, 36, and 37. A built-in motor 28 for rotatably driving the main spindle 23 has a stator 29 fixed to the housing 21 and a rotor 30 fixed to the main spindle 23. The exothermic action of the rotor 30 is transmitted to both end parts of the main spindle 23 by the heat pipe 31 to be absorbed therefrom into water flowing the aquatic static pressure bearing 34, 36, and 37 for releasing to the outside. In addition, a cooling fin 66 provided to one end part of the main spindle 23 is faced to drain passages 61, 63 of the aquatic static pressure bearing 37 to cool the main spindle 23 by water flowing the drain passages 61, 63.