Tool clamping device for main spindle

A tool clamping device for clamping a tool on a main spindle or releasing the same from the main spindle, comprising:

• a main spindle rotatably supported on a headstock;
• a push rod extended through the spindle hole of the main spindle so as to be axially slidable, a weak spring for urging such push rod rearward wherein said push rod is movable axially for fixing a tool to or releasing the same from the main spindle;
• a clamping spring for pressing the push rod rearward;
• a sleeve disposed contiguously with one end of the clamping spring so as to be movable relatively to the push rod;
• first interlocking means formed between the push rod and the sleeve so as to interlock the sleeve with the push rod when the sleeve moves in a direction to allow the expansion of the clamping spring and to release the sleeve from the push rod when the sleeve moves in a direction to compress the clamping spring;
• second interlocking means capable of being disengaged by the movement of the push rod in a direction to compress the clamping spring;
• a tool changing arm;
• and an unclamping cylinder disposed contiguously with the sleeve to move the sleeve against the resilient force of the clamping spring wherein the resilient force of the weak spring urging the push rod rearward is greater than a force that tends to cause the tool to fall off by itself from the main spindle and smaller than the tool pulling force of the tool changing arm and wherein the first interlocking means formed between the sleeve and the push rod further comprises an annular groove formed on a circumference of the push rod, a plurality of balls positioned in said annular groove, and a pressing member for pressing the balls resiliently against the engaging surface of the sleeve, the push rod being retained at a front limit position upon positioning of said balls in said annular groove, after said tool has been removed.