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Lathe collets are used to hold cylindrical stock in a lathe chuck. Manufactured from a wide variety of materials, the typical lathe collets are manufactured from a type of spring steel. The lathe collets are cone-shaped on the exterior, with a straight bore in the center of the collet. The entire collet is divided into several sections that are compressed as the tapered collet is drawn into a corresponding collar in the lathe's power head. As the collet is drawn into the collar, the sections compress around the round stock, thereby clamping it in place through static friction or force.
Many machinists prefer lathe collets over other types of lathe chucks because of the collet's easy setup and the ability to properly center the work piece. Unlike a self-centering chuck, the lathe collets offer a greater degree of accuracy and commonly provide more precision than an independent jaw chuck. In a manufacturing setting, this equates to increased production by decreasing downtime as a worker attempts to center the workpiece in an adjustable lathe chuck. The many contact points of the collet also reduce damage to the working stock by distributing the contact pressure over a wider area of the workpiece when compared to a typical three- or four-jaw chuck.
The size of lathe collets is determined by the size of the bore in the collet. This translates to the size of stock that can be properly secured in the collet. It is common for a lathe to have several different sized collets to allow the operator to work with multiple stock sizes. Each of the collets will have the same outside dimensions and be able to work in a common collar, however, the inner bore size will differ to accommodate various sizes of stock. While some collets are threaded at the base to screw into the collar, thus drawing the taper into the collet and tightening the grip on the stock, other designs are pushed in and held in place through the use of a tail stock and center point.
There are lathe collets manufactured from aluminum, brass and nylon that are intended to be used with soft stock. The soft metal and nylon collets typically will not damage or mar the softer materials surface like the harder, spring steel versions can. These softer collets are often referred to as short time collets due to the limited life of the tool.
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