Abstract: A chuck for a machine tool is disclosed having radially rockable work clamping jaws. These jaws are rocked between work clamping and work releasing positions by radially extending levers engaging axially and rearwardly extending legs on the rockable supports for the jaws. The levers form a toggle-like mechanical lock with the legs of the rockable supports which lock will not permit the jaws to release even though the lever actuating mechanism is not subjected to any restraining force. Further, the disclosure provides a mechanism which is not biased to release by the centrifugal forces incident to the use of the chuck.

Abstract: A diaphragm type chuck is disclosed equipped with means to lock the work engaging jaws against inadvertent release due to centrifugal forces. The means automatically shifts into jaw locking position when the chuck is closed and automatically releases the jaws when the chuck is to be opened.