Why does my router bit keep slipping or creeping out of the collet?
Collets are a sprung sleeve, not a clamp — how they actually grip, the seating error almost everyone makes, and when a collet is simply worn out.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 3 min
- Safety
- warning
Short answer
Insert the bit fully, then withdraw it two or three millimetres before tightening, so the shank is gripped along the collet's whole length rather than bottoming out. Clean both the collet and the shank — dust and resin stop it gripping. Tighten firmly with the proper spanners. If it still creeps, the collet or the nut is worn and should be replaced.
A router collet is a tapered split sleeve that is squeezed onto the shank as the nut pulls it into the tapered nose of the spindle. It grips by friction over the full length of the sleeve, which is why exactly how the bit is seated matters far more than how hard the nut is done up.
Safety
Step by step
- Unplug the router.Every step below involves putting fingers near a cutter.
- Take the collet out and look at it.On most routers the collet lifts out of the nut, or unscrews as an assembly. Compacted dust and hardened resin inside the collet stop it closing evenly onto the shank, and this alone accounts for a great many slipping bits.
- Clean the collet, the nut and the spindle taper.A brass brush and a solvent, then dry thoroughly. Do not oil or grease any of it — lubricant on a friction grip is the opposite of what is wanted, and it collects dust.
- Clean the bit shank.Resin and rust on the shank reduce the grip. A wipe with solvent and a light scuff with fine abrasive on a rusted shank restores it. Discard any bit whose shank is scored, ridged or has a raised burr from a previous slip.
- Seat the bit correctly.Push the shank fully in until it stops, then pull it back out by two or three millimetres and tighten. If the bit bottoms out against the spindle, the nut tightens the collet against the bit's end rather than gripping the shank, and it will creep. Equally, at least three quarters of the shank should be inside the collet — never grip just the tip.
- Tighten properly with the right spanners.Two spanners, or one spanner and the spindle lock, whichever your router uses. Firm and decisive. Over-tightening distorts the collet permanently; under-tightening lets it slip. If in doubt, follow the manual.
- Never use a reducing sleeve as a permanent fix.A sleeve to run a 1/4in bit in a 1/2in collet grips over a fraction of the area and concentrates the load. Fit the router's proper 1/4in collet instead. Adaptors are the single most common cause of thrown bits.
- Replace a worn collet.Collets wear out. Signs are visible bell-mouthing at the ends, scoring inside, a collet that no longer springs open when the nut is loosened, and bits that mark the same ring on every shank. They are inexpensive relative to a router and to a workpiece, and replacing one is a five-minute job.
- Never leave a bit in the collet between jobs.Left clamped, the collet takes a set and the bit can rust in place. Loosen and remove bits when you finish.
Tips
- If a bit has slipped once, inspect the shank. A raised burr where it was gripped will stop it seating properly ever again and can jam it into the collet.
- Keep the router's spanners with the tool. A bit tightened with pliers or an adjustable spanner is a bit tightened wrongly.
- Buy the manufacturer's collet rather than a generic one. The taper angle has to match the spindle exactly.
If it doesn't work
Bit creeps down mid-cut and the profile gets deeper
Cause: Bit bottomed out in the collet, or a dirty collet — Fix: Reseat with the bit withdrawn a few millimetres from the bottom, after cleaning both collet and shank.
Bit spins in the collet and scores a shiny band on the shank
Cause: Insufficient grip — worn collet, contaminated surfaces, or under-tightening — Fix: Clean everything, tighten properly. If it recurs, replace the collet and the nut as a pair, and discard the scored bit.
Collet will not release the bit when loosened
Cause: The collet is designed to be pulled out of the taper by the nut; the nut has not been slackened far enough, or the collet is seized in the taper — Fix: Keep unscrewing — there is usually a distinct second release point. If seized, remove the collet assembly and clean the taper.
Bit vibrates and the cut has a rippled surface
Cause: Bit not seated square, a bent shank, or a distorted collet — Fix: Reseat and check the shank by rolling it on a flat surface. Replace anything bent.