The Change To Quick-Change Collets

In many high-tolerance applications involving relatively small parts, collets can provide the best workholding capabilities. While somewhat limited in the range of workpiece sizes they can typically accommodate, their benefits in production times and accuracy make them a smart consideration. The collet can provide tighter concentricity by making contact throughout the circumference of the part.

Changing collets because they are worn or broken to accommodate variations in barstock diameters also can have a significant impact on the time it takes to complete a part. Making the change with a standard collet system typically requires several minutes, using a wrench to unthread the collet, removing the washers and reassembling the new collet. In the right applications, however, decreased change-over times from one job to the next could be achieved simply by adding a quick-change collet system to the turning operation.

The Workholding Division of Hardinge, Inc. (Elmira, New York) now offers the HQC quick-change collet system, designed to allow faster change-over than standard collets and to be more flexible than master collets and pads. Available for use on multi-spindle automatic screw machines, Hardinge collet-ready CNC lathes and other chuck-style CNC lathes with A2-5, A2-6 and A2-8 spindles, the system can accommodate barstock variation and provide the opportunity for increased spindle speeds. The flexible collet head offers true parallel gripping with the collet segments running parallel to the stock, even when there are variations in the stock size. The collet head has a working range of ± 1/64 inch for diameters smaller than 2 inches, and ± 1/32 inch for 2-inch diameter and larger on automatic screw machines, and a range of - 1/64 inch to + 0.008 inch on CNC lathes. Parallel clamping minimizes stock “push back” and requires less drawbar force than conventional collets. By applying more gripping force and providing high concentricity control, the system allows for higher feed rates and spindle speeds.

With a manual or hydraulic changing wrench, the quick-change system can be changed from one size collet to another in less than 20 seconds. The wrench compresses the collet, allowing for quick removal and installation of a different size collet head. In a multi-spindle setup, the time savings of the fast collet change-over can be multiplied for each spindle.

Because solid collets and master collets are designed with one-piece construction, considerable force is required to flex the leaves and bring the gripping surface in contact with the workpiece OD. The HQC system does not have leaves, so additional gripping pressure is available to be applied directly to the workpiece. Higher feed rates and higher spindle speeds are therefore possible, tool life increases and parts come off of the machine more quickly. Also, with less drawbar force needed to adequately grip the bar, closing fingers and pins are less likely to break when the bar diameter varies to beyond what would be the range of a standard solid collet or master collet with pads.

The HQC collet heads are designed with replaceable inserts that form a seal while holding the collet segments together. The seals protect the spindle, collet body and draw tube from chips and coolant for direct cost savings and time savings. The slot-seal system on the HQC eliminates the need to return the collet to the manufacturer to have the seals changed or re-vulcanized. The inserts can be replaced in the shop by the machine operator, further reducing operating costs.

The quick-change collet system can be used on chuck-style lathes to replace three-jaw chucks. The reduction in weight and the efficient design with clean contours allow increased spindle rpm without any concern for centrifugal forces.

If you’re thinking about adapting your chuck-style lathe to accept collets for high-precision work, the HQC quick-change collet system might be a good alternative. It is shorter than standard collet adapters, thus gaining more working area and allowing machining closer to the spindle. For achieving better total indicator reading (TIR) on finished parts, this system might provide the advantages you need.