Spindle unit for a machine tool

摘要

The present relates to a spindle unit for a machine tool having a spindle rotatably held in a housing and a hydraulic tool holding system at a forward end of the spindle and capable of holding a tool on the spindle without a tool holder. The spindle of the spindle unit is provided with a tool receiving bore formed in the forward end portion of the spindle along the rotational axis thereof, one or more pressure chambers disposed around the tool receiving bore in spaced relationship from the tool receiving bore by a thin wall elastically deformable in a radial direction of the spindle, and a working fluid passage formed in the spindle and in fluid communication with the one or more pressure chambers. The spindle unit further includes a pressure adjusting device arranged in the rear portion of the spindle unit and connected to the pressure chamber through the working fluid passage. The pressure adjusting device adjustably changes the pressure of the working fluid within the pressure chamber so that it can elastically deform the thin wall to enlarge or reduce the tool receiving bore in radius, thereby holding or releasing the tool inserted into the tool receiving bore.