In a machine tool such as a milling machine, the work to be machined is mounted to a table.  The table is movable relative to a machining head having the tool, such as a cutter, to position the piece to be machined, the work piece, relative to the machining tool.  In order to position the work relative to the machining head, the table is movable by the table being slidably mounted to a second movable unit, commonly referred to as a saddle which in turn is movable relative to a third movable unit, commonly referred to as a knee.  This last movable unit, the knee, is movable relative to the base of the machine tool.  By adjusting the position of each of the movable units, the table with the workpiece can be positioned vertically, transversely, and longitudinally relative to the base and the machine head of the machine tool.  Once the table has been adjusted relative to the base and the machine head, it is critical that the table be maintained in a fixed position relative to the base while the work piece is being machined on the table. 
This invention relates to a clamping device for a machine tool.  The machine tool typically has a work table and a saddle.  The worktable is slidably mounted to the saddle.  An elongated table screw is carried by the work table in a preferred embodiment.  A threaded block is carried by the other unit, the saddle, and threadably receives the elongated screw. 
The clamping device has a frame that is securable to the worktable.  A pair of jaws each have an acurate surface for engaging the elongated screw.  A mechanism moves the jaws relative to each other and into a closed position engaging and retaining the elongated screw. 
In one embodiment, one of the jaws is fixed to the frame and the other jaw, a movable jaw, is movable relative to the fixed jaw and the frame.  The movable jaw is movable by rotation of a threaded screw carried by the frame and having an end engaging the movable block. 
In one embodiment, the clamping device has a base attachable in a fixed position relative to the work table and a pair of clamping jaws slidably mounted on the base for movement toward and away from each other.  The jaws are linked to the base and to each other so that movement of a first one of the jaws toward a second one of the jaws causes the second jaw to move toward the first jaw.  An actuator is connected to one of the jaws for moving the jaws toward one another for clamping the longitudinal screw to prevent the screw from rotating. 
In one embodiment, one of the jaws or blocks has a projecting tooth receivable in the groove between a pair of threads in the elongated table screw.  The projecting tooth is moveable in one direction, such as vertically, relative to the jaw. 
In one embodiment, an adjustment screw is carried by the clamp frame to space the clamp frame from the work table.  A spacer is interposed between the adjustment screw and the work table.  A T-bolt is carried by the clamp frame and receivable in a slot in the work table to secure the clamping device to the work table. 
In one embodiment, one of the jaws has a slot for receiving a guide pin of an actuator.  The slot is at angle relative to the perpendicular direction to the motion of the jaw.  An insert has a plurality of arcuate surfaces to receive the guide pin is receivable by the slot.