A collet is a metal band placed around a wooden pole to prevent it from splitting. In manufacturing, a collet is a type of chuck used to hold cylindrical objects in a lathe. This type of chuck is a metal cone-like device that surrounds the work piece and applies an equal amount of holding pressure to the entire circumference of the piece.
Typically found on lathes, grinders and milling machines, the collet is know for its extreme accuracy. Much more accurate than a multi-jaw type chuck, the collet holds the work piece to exacting tolerances. Its downside is that it typically fits only one size of work piece. The chuck is, however, very easily changed when the need to work on a different size of stock arises.
While the collet is designed to primarily work with round stock, octagonal, square and even hexagonal work pieces can be used in the chuck. Many manufacturers utilize this type of chuck when completing very precise operations and doing very detailed work. Special emergency-type collets can be machined to hold different shapes of stock as well as different sizes.
Most chucks are made of special hardened steel to withstand many use cycles, as would be typical in a high-volume manufacturing environment. There are, however, collets made of brass and even nylon that can be custom made to hold special work pieces. These chucks can also be made in step models that are machined to hold shorter pieces that have a larger diameter than the standard size chuck.
There are several advantages to using a collet chuck over a self-centering or multi-jaw type chuck. To decipher which type of chuck to use there are some key points to consider. Spindle speed is crucial to chuck choice. A high-speed tooling requires the lower mass chuck over the higher mass and weight of a self-centering chuck. The lighter weight and less mass allows the chuck to accelerate in a much faster manner.
When working on a large run order or creating many identical pieces, the collet allows for easy stock changing and precise holding. Also, when the parts are of a diameter of less than three inches, this type of chuck is preferred due to its holding power and easy operating tendencies. When making multiple operation cuts on a work piece, the collet provides a much tighter clamping tolerance, thereby ensuring that the outcome of the different steps will be precise.