CHUCK FOR MACHINE TOOL

PURPOSE:To make it possible to shorten the operation stroke of a plunger and strengthen and stabilize jaw seating by arranging a means to lock jaws to a master jaw with the jaws holding a means to seat the jaws to the master jaw forcibly between themselves. CONSTITUTION:When a master jaw 4 starts to slide radially and stops at a controlled position and the bottom 28 of a V shaped wedge section 17 and the end 29 of a DELTA shaped wedge section reach an area on the same line, a piston 20 is raised by a controlled pressure medium. In addition, the wedge sections 17 and 14 abut and slide to each other along with the shift of the jaw 3 in the outer peripheral direction for giving energizing return pressure to a clamp pin 6. As a result, an energized coil spring 12 is compressed, and the wedge section 13 of the central section of the pin 6 is also retreated to engage a clamp stand 5 rising by aid of the energizing force of a coil spring 8. At this point, the pin 6 and stand 5 are slidden in the radial direction of the jaw 3 holding strong energizing force for firmly locking a jaw 21.