By David A. Stokely, SpeedGrip Chuck guest posting One of the most vexing problems in machining today is how to most efficiently make an out-of-round part round. In the days of thick-walled tubing or cut slugs, this manufacturing task presented little difficulty, but with today’s thin walled near-net-shape parts, the difficulties mount. Fortunately, we have developed several ways to make this task much easier. It takes three points to define a plane. This fact of geometry is why a three-legged stool or table will never tip. No matter what uneven shape the floor beneath may have, three points of leg contact will always be able to find a flat plane defined between them and therefore not tip.
After the clamps actuate, the push-on collet retracts out of the way, so that the full part bore may be turned and the outer face can be machined inside of the clamps for a second operation flat locating face. This is a custom-designed mechanism. We have many different styles of clamp and centering devices. The style of chuck can be configured to virtually any required configuration. Other common options included in this design are through the spindle coolant flush, part air confirmation circuits, and carbide or diamond coating of the clamps or work stop pads.
The latest entry into our non-rounding arsenal is the finger collet. Having similarities both to a diaphragm chuck and a collet chuck, this mechanism is an economical alternative to a multi-jaw chuck.
Of special importance, we require to know the maximum out-of-roundness that may be encountered in the part as it comes to this operation, and the required roundness and flatness of the machined surfaces. Figure 4 is an internal gripping finger collet. The part was a 13-inch ID 4340 forging. The forging coming to the operation, was roughly 0.100 out of round.
The same issue that exists with non-rounding during machining is also an issue during the part inspection process. The same 13” 4340 casting part that we held for machining on the first operation also needed to be inspected on a gear checking inspection machine. (Figure 5)
Not totally confident of such a new and easy method of checking their parts, the customer had the first hundred or so parts indicated after being chucked in the push-on collet. When no misloads were discovered, the push-on collet was trusted with a very important operation. The comment was made by the customer that this was the best tooling investment that they had made in a long time.
They can be splined to check concentricity and squareness of a gear’s pitch, minor, or major diameter.
They can be polymer-coated and have been used in sizes ranging well under an inch to more than 20 inches in diameter.
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