The mechanics of turning don't tend to offer up dramatic new developments all that often. But this just may be an exception. It's a new high speed chuck that, according to The Goss & DeLeeuw Machine Co. (Kensington, Connecticut) can achieve 10,000 rpm with no loss in gripping force without the use of a conventional counterweight system.
For those people familiar with high speed chuck designs, this might seem to be claiming the impossible. But the critical distinction here is the term "conventional." The chuck does use a counterweight of sorts, but the ingeniously simple design is unlike any chuck you've ever seen.
Typically, high speed chucks use a counterweight mechanism within the chuck body that works to offset the effects of centrifugal force on the chuck jaws. In essence, each jaw is connected to a weight of equal mass, and the two seek to move in opposite directions as centrifugal forces are applied to the system. If all is in order, as the chuck spins, the opposite forces cancel each other out.
The system works well in many applications, but does have its limitations. Most notably, the mass chosen for the counterweight necessarily presumes a specific mass on the other end of the line. But there are two main reasons why this presumption may not hold true. First, many shops use more than one set of top jaws, which of course will differ in mass. While that may seem a trivial difference, at very high speeds it can cause a significant loss in gripping force if the top jaws are heavier than nominal, or cause excessive pressure on the workpiece if the jaws are lighter than nominal. Moreover, where the jaws are positioned in their stroke can have a significant effect. The larger the diameter of the grip position, the greater the force pulling the jaws outward.
So, while conventional high speed chucks offer substantially improved performance over standard chucks at high speed, they still usually exhibit growing loss or gain in dynamic gripping force as the rpms run higher because it is impractical to get a perfect counterweight offset for each application.
Not so with the new Goss & DeLeeuw chuck. Instead of locking the counterweights inside the body, they are placed right on the face of the chuck (see photo). That is, each jaw is mechanically linked to the wedge shaped weight located directly opposite. By loosening a single screw, the counterweight can be removed and then machined to bring it to an appropriate mass for the turning process at hand. And the chuck will exhibit no significant change in gripping force across the entire rpm range. To prove out that claim, pneumatically actuated 6-inch chucks have been tested up to 10,000 rpm, and 10-inch hydraulic chucks have been tested up to 7,000 rpm.
The new chuck is available in accuracies ranging from 3 "tenths" to 50 millionths of an inch. It also features quick change jaws that are fixed with a single bolt, and that can be changed without the need for reboring in most applications. All units are sealed, permanently lubricated and maintenance free.