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A collet is a small part with a big effect on machining accuracy. It holds a tool or workpiece on center, and when it wears, you see it in runout, finish and tool life.

What a collet does

A collet is a slotted sleeve with a tapered outside. When a nut or drawbar pulls it into a matching taper, the slots close and the bore grips the tool or part evenly around its circumference. That even grip keeps the tool concentric and reduces vibration.

Common collet types

• ER collets: Common on CNC mills and machining centers for end mills, drills and taps. Each size clamps over a small range of shank diameters.
• 5C collets: Common on lathes, grinders and workholding fixtures for round, square and hex stock.
• R8 collets: Used in the spindles of many knee mills, held in place by a drawbar.
• Spindle collet assemblies: The clamping assembly inside a machine tool spindle that grips the tool holder's retention knob. Collet assembly 850412-00052 is one example, built for DIN 40 taper spindles.

Materials

Most collets are hardened spring steel, which can flex through repeated clamping cycles and return to shape. Carbide is used in some high-speed work for its hardness and wear resistance. Stainless versions suit environments where corrosion is a concern.

Signs a collet needs replacing

• Runout has increased, even with a clean holder and a good tool.
• Tools slip or pull out under load.
• Surface finish gets worse or chatter appears without a change in the process.
• The taper shows fretting, scoring or discoloration.
• Slots are cracked, or the bore shows visible wear.

How to get more life from a collet

• Clean the collet, nut and taper at every tool change. Chips on the taper cause runout.
• Use the collet within its stated clamping range.
• Tighten to the manufacturer's torque value. Too much can damage the collet, and too little can let the tool slip.
• Keep collets dry, lightly oiled and stored away from chips.

Finding the right part

For a spindle collet assembly, start with the OEM part number, the machine model and the taper size. Browse our collets, or call 847-466-5459 with your machine details.