Spindle clamping device for machine tool

A spindle clamping device for a machine tool for clamping a spindle assembly supported by a spindle head and composed of a first spindle rotatably supported by the spindle head and a second spindle rotatably supported inside the first spindle to be reciprocal along an axial direction thereof, said first spindle having an inner hollow portion and said second spindle being inserted into said inner hollow portion of the first spindle so that a space is formed between an inner peripheral surface of the first spindle and an outer peripheral surface of the second spindle, said spindle clamping device comprising:

• pressure applying means disposed in the space between the first and second spindles for applying a pressure in an axial direction of the first and second spindles, said pressure applying means being provided with an oil chamber;
• at least a pair of clamp rings disposed in the space axially outside the pressure applying means, each of said paired clamp rings comprising a first ring element having one surface contacting the outer peripheral surface of the second spindle and another surface tapered downwardly outward of the pressure applying means and a second ring element having one surface contacting the inner peripheral surface of the first spindle and another surface slidably contacting the tapered surface of the first ring element;
• elastic means disposed in the space axially outside the clamp rings, respectively, for urging the second ring element inwardly;
• and
• a static pressure pocket formed to a contacting portion of the spindle head supporting the first spindle wherein a pressurized oil or an air is supplied into the oil chamber through the static pressure pocket.