Tool clamping device for a spindle head

A tool clamping device used with a machine tool is provided for clamping a tool on a tool spindle. In a bore of the tool spindle, there is axially movably received a guide bush which is formed with a recess for permitting steel balls to retract toward radial outward directions. A retainer for holding the steel balls is received in a bore of the guide bush for axial movement relative thereto. The guide bush is connected to a draw bar which is axially movable in the bore of the tool spindle and which is spring-biased toward a rearward direction of the tool spindle. Thus, when the draw bar is spring-drawn toward the rear end of the spindle, the steel balls are restrained from radial outward movements through engagements with the internal surface of the guide bush thereby to clamp the pull stud of the tool. However, when the draw bar is moved toward the front end of the spindle against the biasing force of the spring, the steel balls are retracted into the recess of the guide bush thereby to release the pull stud of the tool.