Patent ID: 7874771

Claim:
A milling spindle of a machine tool comprising: a rotary spindle supported via a bearing within a housing of the milling spindle; a motor disposed within the housing for driving the rotary spindle directly; a drawbar inserted slidably within the rotary spindle; a through coolant passage disposed in an axial center of the drawbar for supplying cutting fluid; a rotary joint disposed on a rear end side of the drawbar and sending the cutting fluid supplied from a fixed side of the rotary joint toward the rotary spindle being rotated; a drain chamber disposed within the housing for storing the cutting fluid leaking from the rotary joint; a rotation member attached to a rear end portion of the rotary spindle and facing the drain chamber; an air supply member fixed to the housing and facing the rotation member; an air sealing device attached to the air supply member and making up an air seal with the rotation member; and a labyrinth device having a lip seal member for preventing the cutting fluid in the drain chamber from entering the space in which the motor is disposed.