PURPOSE:To prevent a motor and a pulley from generating heat to aim at stabilizing the machining accuracy of workpieces, in a machine tool in which an insulator is disposed between a main spindle head and the motor, by forming ventilating grooves and air-intake holes in the insulator and the pulley, respectively. CONSTITUTION:Heat transmission shield plates 4, 5, 6 each of which is formed by incorporating a heat radiating material having a high heat conductivity on the outer surface of an insulator having a low heat conductivity are disposed between a main spindle head 1 and a motor 2. In this arrangement the plates 5, 7 having a larger area and the plates 4, 6 having a smaller area are alternately combined to increase the heat radiation area. Further, a plurality of ventilating grooves 4c, 6c are formed in the plates 4, 6 radially of the shaft 2a of the motor. Then, a cooling fan 11 is secured to a pulley 10 through which a plurality of axial air-intake holes 10a are formed to pierce. With this arrangement it is possible to prevent the motor 2 and the pulley from generating heat, and therefore, there is not fear of thermal deformation of the main spindle head due to heat transmission. Accordingly, the machining accuracy may be enhanced.
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