When draw-bolt 1 is pulled to the left by the chuck-operating device (not shown), it pulls sleeve 2 to the left and its shoulder a forces spherical equalizing members 3 against the conical surfaces of sleeves 4 and 5. Sleeve 4 has two openings for the ends of diametrally opposed bell-crank levers 6 whose other arms engage slots in jaws 7. Sleeve 5 has four openings, two through which levers 6 pass with a large clearance, and two for the ends of diametrally opposed bell-crank levers 8 whose other arms engage slots in jaws 9. The drawing is a conventional section view, with its upper half being a section through one of the jaws 7 and the lower half through a jaw 9. The two sections are actually at an angle of 90° to each other. Sleeves 4 and 5 turn the two pairs of opposing jaws 7 and 9, until one pair contacts and centres the workpiece. At this, the sleeve linked to this pair of jaws stops and the second sleeve continues to move to the left, owing to the radial displacement of equalizing members 3, until the second pair of jaws also contacts the workpiece. When all four jaws contact the workpiece, it is finally clamped. The workpiece is released by reversing the motion of draw-bolt 1.
$3076$SmC,ML$