Milling spindle of machine tool

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.