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Better Grip for More Durability, Functionality

Oct. 20, 2011
Expanding collet systems with through-hardened, interchangeable heads
Hardinge Sure-Grip expanding collet systems are designed for long production runs, and to achieve superior surface finishes and fast collet changeover from the front side of a machine.

Hardinge Group’s Sure-Grip expanding collet systems are a patented, one-piece body design that use precisely sized, through-hardened collet heads that will interchange with all assembly sizes from machine to machine. The collet heads have an under-over capacity of -0.001 to +0.015 in. (-0.025 to 0.38 mm) from its specified size to accommodate a range of part diameters.

Many expanding collet systems are designed to use soft, machineable collet heads that require extra time to machine to size; or are not durable for long production runs; or are not keyed for repeatability. Hardinge through-hardened collets are keyed for accurate part positioning for repeatable performance.

The double-angle design offers true parallel gripping — meaning that the collet expands equally over its entire length rather than at just one end, providing maximum bearing contact against the part. This results in greater stability and better part accuracy. Parts are instantly centered and located without adjustment. Higher speeds (rpm) and greater feed rates offer shops the ability to produce more parts-per-hour.

The Sure-Grip system also features a built-in safety stop to prevent the collet from over-expanding.

During chucking operations, parts can be located against the face of the arbor or against a machineable workstop. This provides exact part-length control as well as improved part consistency. The expanding collet draws the part firmly against the stop, producing an extremely stable part location. Longer parts are easy to machine due to this greater degree of stability. The results are heavier cuts, better surface finishes and closer tolerances when using a workstop. Short grip lengths can be held firmly when the part is pulled back against a workstop. When machining just the OD of the part, workstops may not be necessary.

Machines or devices with ANSI type-A spindles and machines with collet-ready spindles or collet adapters can use the Hardinge system. 5C, 16C, and 3J collet-style expanding collet systems mount directly into the collet angle of the spindle or in fixtures (collet blocks) with instant centering. There are no spindle adapters required. A2-5, A2-6 and A2-8 expanding collet systems will mount directly on the spindle. Hardinge also manufactures center arbors that use Sure-Grip expanding collets for grinding machines, lathes and other applications that can be held between centers, or chucked on one end and supported by a center on the other end.

There are instances where an expanding collet may shorten cycle time, reduce waste, or simply hold a hard-to-grip part. An expanding collet may eliminate the expense of manufacturing a custom fixture or collet, or eliminate secondary machining, according to Hardinge. An expanding collet will grip a thin-wall part without crushing or distortion and prevent damage to threaded outside diameters, it added.

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