Power-operated work clamping devices

A power-operated work clamping device comprising a housing having a central bore, a tubular piston non-rotatably positioned in said bore and axially movable therein in response to the application of fluid pressure, means in said housing engaging said piston for restraining rotation thereof, and a clamping member having a connecting rod extending into said housing and fitting within said piston for relative angular and axial movement thereto, said piston being connected to said connecting rod by a projecting means from one of said piston and said rod and a co-operating cam slot in the other of said piston and said rod and into which said projecting means extends, said cam slot being shaped so that axial movement of said piston over a first distance in one direction produces a first angular movement of said connecting rod and clamping member, and thereafter axial movement of said piston over a second distance in said one direction produces a second axial movement of said connecting rod and said clamping member when said projecting means has reached the end of said cam slot, said cam slot being of a length to extend for said first distance and to end at the end of said first distance, axial motion restraining means located in said housing and positioned to be engaged by said connecting rod to prevent motion of said connecting rod in said one direction during angular movement thereof, whereby said connecting rod is restrained against axial movement during movement of said projecting means along said co-operating cam slot.