Hardinge Inc. manufactures a line of lever-operated, counter-centrifugal and dynamically balanced chucks — the Sure-Grip® Power Chuck series. The lever-operated design imparts several advantages over the wedge-type designs that are commonly found on low-cost, non-counterbalanced chucks supplied with the initial purchase of many chuck-style lathes.
In the Hardinge lever-operated system, the drawtube is connected to the jaws through a pivoting lever that is mounted on pins inside the chuck body. The lever system has reduced friction and increased mechanical advantage compared to a wedge-operated chuck for a given draw bar pressure. In other words, a lever will always have greater actual gripping power at the jaws than a wedge-operated chuck, for any given draw bar pressure.
The lever system also has reduced internal bearing surface over the wedge-operated closure, making it less sensitive to lack of lubrication. The greater efficiency of the design results in reduced wear on the operating cylinder, increasing component life dramatically, according to the developer. For this reason, a lever-operated system (chuck and operating cylinder) usually will have a longer life than that of a wedge-operated system.
In the Hardinge counterbalanced chuck design, weights are incorporated into the actuating levers of the chucks at the opposite end of the fulcrum or pivot-point of the jaws. Centrifugal force acts upon this weight just as it does on the top jaws. However, because the weight is at the opposite side of the lever from the top jaws, the upward thrust generated counteracts some of the jaw force loss. Thus, the counterbalanced lever design has substantially more gripping force at high RPM than that of a non-counterbalanced style.
The major advantage of the Sure-Grip power chuck is the configuration of the drawtube that actuates the chuck. Because all Hardinge machines have collet spindles that do not require a collet chuck or adaptor, it is a simple matter to remove the collet and quickly mount the three-jaw Sure-Grip power chuck when needed. The chuck’s drawtube threads directly into the machine’s draw bar, just as a collet would. This changeover can be accomplished in ten minutes or less, whereas other designs may take hours to complete.
The Sure-Grip power chuck is also available for non-Hardinge lathes that do not have collet style spindles.
Hardinge noted that it manufactures its chuck components to high accuracy and repeatability standards. The repeatability of a chuck is the measure of its ability to repeat the performance, either from job-to-job or from part-to-part. Most models of Hardinge Sure-Grip power chucks have an accuracy (T.I.R.) of 0.0005 inch and repeatability of 0.0005 inch, making them ideal for close tolerance turning requirements.
