GlossaryKind of term: Manufacturing termChuck and collet
What are chucks and collets?
Chuck and collet are the two common ways to hold work on a lathe spindle: jaws that clamp radially, or a slotted sleeve that grips all round.
A chuck is workholding on the lathe spindle with jaws that move radially onto the workpiece. The common self-centring chuck has three jaws that move together; there are also two-, four- and six-jaw versions, and four-jaw chucks with independently adjusted jaws for eccentric or irregular work. On CNC lathes the chuck is usually power-operated, often hydraulically. A collet is a slotted sleeve with a taper that is drawn or pushed into a collet chuck and grips the workpiece all round. Each collet has a small clamping range, but it centres accurately and grips over a large part of the circumference.
What accuracy do chucks and collets give?
The dimensions you can hold depend on the workholding, the jaws, the clamping force and the workpiece. The centring accuracy of a chuck with hard jaws is limited and varies from one clamping to the next; soft jaws bored in the chuck under clamping force, or a collet, usually give lower runout. Three jaws can distort a thin-walled ring into a triangular shape; it springs back after release and is no longer round. More jaws, pie jaws or a collet spread the force better. With external clamping, the centrifugal force on the jaws reduces the effective clamping force at high spindle speeds, and heavy soft jaws add to that. A chuck therefore carries a rated maximum speed.
How do chucks and collets work in practice?
The choice affects setup time, repeatability and the risk of jaw marks. A chuck with hard jaws changes over quickly for varying diameters and one-offs, but can mark a machined surface. A collet is common for bar work, on Swiss-type lathes and for small diameters in batches; each bar diameter usually needs its own collet. On a second setup with tight runout or coaxiality between front and back, the workholding helps decide whether you meet the requirement without rework.
What are chucks and collets often confused with?
A self-centring chuck is not a four-jaw independent chuck: that one is set jaw by jaw and does not centre by itself. A faceplate is a flat plate to which the workpiece is bolted with clamps or angle plates. And a workholding collet on a lathe is not the same as a tool collet in a milling spindle: the principle is the same, the job differs.
Frequently asked questions
When do you choose a collet over a chuck?
For bar work, small diameters and batches where centring, quick changes and grip all round count. A chuck is handier for varying or larger diameters, short runs and rough stock that falls outside a collet's clamping range.
Does the workholding decide the runout?
In part, especially on a second setup. A collet or soft jaws bored in the chuck usually give lower runout than hard jaws. The machine, the workpiece and the clamping force play a part too.
Why does a thin ring distort in a three-jaw chuck?
Because three jaws apply the force at three points. The ring is pressed into a triangular shape, turned round in that state and springs back after release. More jaws, pie jaws, a collet or a lower clamping force limit that.