Spindle device and machine tool

A spindle device comprising:

• a housing;
• a spindle of which a part close to one axial end is rotatably supported to the housing by a rolling bearing or a rolling bearing unit and of which one axial end portion is mounted with a tool when using;
• and
• an electric motor configured to rotatively drive the spindle;
• wherein the electric motor is configured such that an inner peripheral surface of a stator supported to the housing faces an outer peripheral surface of a rotor supported and fixed to an axially intermediate portion of the spindle;
• wherein a radially central portion of the spindle is formed with a through-hole configured to axially penetrate the spindle,
• wherein radial venting holes configured to communicate an outer peripheral surface and an inner peripheral surface of the spindle are provided at a plurality of circumferential locations of a part closer to one axial side than a part, to which the rotor is supported and fixed, of the axially intermediate portion of the spindle,
• wherein axial venting holes configured to communicate one axial end face of the spindle and inner peripheral surfaces of the respective radial venting holes are respectively provided at a plurality of circumferential locations of one axial end portion to the axially intermediate portion of the spindle,
• wherein discharge holes configured to communicate the outer peripheral surface of the spindle and inner peripheral surfaces of the respective axial venting holes are respectively provided at a plurality of circumferential locations of a part positioned closer to one axial side than a part, to which the rolling bearing or the rolling bearing unit is externally fitted, of a part close to one axial end of the spindle.
• wherein an outer diameter-side opening of each radial venting hole is closed by an inner peripheral surface of the rolling bearing or the rolling bearing unit or another member externally fitted and fixed to the outer peripheral surface the spindle,
• wherein one axial end portion of the housing is provided with a closing plate,
• wherein an inner peripheral surface of the closing plate closely faces the outer peripheral surface of a part, which is between the part to which the rolling bearing or the rolling bearing unit is externally fitted and the part at which the respective discharge holes are provided, of the part close to one axial end of the spindle via an annular gap,
• wherein an outer diameter side opening of each discharge hole is positioned at a more radially inner side than one axial side opening of the annular gap, and
• wherein when using the spindle device, a cooling gas is fed from the other axial opening of the through-hole and is discharged from each discharge hole through each axial venting hole and each radial venting hole.