Most CNC lathes and turning centers are equipped with a standard workholding system consisting of a three-jaw power chuck, a hydraulic drive cylinder, and a drawtube. The hydraulic cylinder is mounted on the rear end of the spindle, while the chuck is mounted on the front or work side of the spindle. The cylinder and chuck are typically connected by a hollow steel telescoping tube that passes through the spindle bore.
Similarly, CNC collet chucks are mounted on the front of the CNC lathe spindle and are driven using the machine’s existing cylinders and draw tubes.
The axial movement of the hydraulic actuator piston causes the jaws of the collet chuck to open and close. The telescopic tube moves in sync with the piston, driving a wedge-shaped plunger inside the collet body as the piston slides back and forth. In turn, the plunger converts the axial motion into a radial motion, completing the opening and closing of the jaws. The clamping force of the jaws on the workpiece corresponds directly to the output of the actuator; therefore, this force can easily be adjusted by means of a pressure valve.
Of course, a collet chuck requires a collet to function. Typically, the clamping range of the collet is approximately 0.062″. Collets are available for round, hex and square stock. Collet chucks can handle a fairly wide range of collets (e.g. 3/16″ to 2-5/8″). Special collet requirements can be accommodated. Most modern collets have a quick (e.g., 10-second) changeover feature to reduce setup time.