Collet

A collet is a holding device used to grip a cylindrical workpiece or tool by applying uniform radial pressure. It consists of a sleeve with a tapered outer surface and a split, segmented inner bore. When the collet is clamped by a nut or holder, the segments are drawn inward, reducing the inner diameter and securing the object with high concentricity.

Construction and operation: Collets are typically constructed as a multi-segment cylindrical sleeve with longitudinal slots. The tool or workpiece is inserted into the inner bore, and the surrounding nut or collar pulls the collet into a tapered seat. This action closes the segments evenly around the shank, producing a precise, repeatable grip with low runout compared with many other holding devices.

Types and applications: Collets come in several families tailored to different machines and needs. Lathe setups commonly use 5C collets for turning operations, while milling and CNC work frequently employ ER collets for a wide clamping range and high concentricity. Other systems include various toolholder collets such as SK or BT. Collets are used on lathes, milling machines, drill presses, and grinding machines to hold tools (such as end mills or drill bits) or small-diameter workpieces.

Advantages and limitations: The main advantages are high gripping force relative to size, uniform contact along the tool or workpiece, and improved accuracy and repeatability. Collets also permit faster tool changes in some setups. Limitations include a limited range of diameters per collet size and potential damage if mishandled or overtightened; they can be more expensive per diameter unit than some chucks and require compatible holders or chucks.