chuck
A mechanical device that holds an object firmly in place, for example holding a drill bit in a high-speed rotating drill or grinder.
chuck: the clamping jaws that grip your work
A chuck is a clamping device that grips and holds a workpiece, tool, or material securely while work is being performed on it. The most common application is holding a rotating drill bit or cutting tool on a machine tool, but chucks appear wherever something needs to be held steady against significant force, vibration, or eccentric loading.
The basic design uses multiple hardened steel jaws (usually three or four) that close inward around the object being held. The jaws are driven by a tapered screw thread or a system of rotating cams, both of which convert a single rotational or axial movement into synchronized jaw closure. When you tighten a drill chuck with the key, you are turning a spiral that forces all jaws inward at once, creating clamping pressure that increases as you turn. A well-designed chuck maintains concentricity, meaning the held object stays centered and does not wobble.
Three categories dominate industrial use. A keyed chuck requires a separate tool (the chuck key) to tighten and loosen the jaws; you must remove this key before operating the machine, or it becomes a flying projectile. A keyless chuck uses a hand grip or ratchet mechanism that eliminates the key but often sacrifices some clamping force. A collet chuck uses a split tapered sleeve rather than discrete jaws and provides excellent runout accuracy for precision work, especially on lathes and high-speed mills.
Size matters in chuck selection. A chuck is specified by the size of its bore diameter and its maximum gripping range. A typical drill chuck might grip bits from 0 to 13 millimeters; a large lathe chuck might handle workpieces up to 200 millimeters in diameter. The jaws themselves wear with use and can be replaced independently. Runout (the deviation from true center) depends on jaw condition, bore wear, and how firmly you tighten; precision applications may require runout under 0.05 millimeters.
Failure modes include jaw slippage under cutting loads, stripped screw threads that prevent full clamping, and concentricity drift that causes vibration and chatter. Chucks must be kept clean of chips and coolant, as debris prevents full jaw closure. The name comes from the old woodworking term for a clamp or vise, borrowed from Middle English.