| 摘要 |
A chuck apparatus including a plurality of radially movable jaws for gripping a drill rod, each jaw being moved radially by an axially movable bowl, each jaw and the corresponding bowl surfaces are provided with two sets of camming surfaces, the first set of camming surface being oriented with a steeper angle than the second set of camming surfaces. In operation, as the bowl moves relative to the jaws with the respective first set of camming surfaces of the jaws and the bowl in contact, the jaw gripping force is relaxed and the jaws release the drill rod. As the bowl and jaws continue to move they transition to interact at their respective second set of camming surfaces whereupon, because the shallow angle of interface, the jaws are moved through a greater distance than if the first set of camming surfaces' steeper angle of interface were employed. As a result, more clearance is provided for freeing the drill rod.
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