Why Your Drill Bit Keeps Slipping (And How to Stop It)

Nine times out of ten, a drill bit that spins uselessly while the motor whines is not gripped properly by the chuck. Either it was not tightened hard enough, the jaws are worn or clogged with dust, or the shank is the wrong shape for the chuck you are using. The other kind of slipping, where the bit skates across the surface before it bites, is a completely separate problem with a completely separate fix.

First, work out which kind of slipping you have

Stop and watch what is actually moving. If the chuck is turning but the bit stays still inside it, or you can see the bit rotating independently of the jaws, that is chuck slip. If the whole bit and chuck turn together but the tip wanders around on the surface without cutting in, that is bit skate. If everything turns properly and the bit sits in one spot but no material comes out, the bit is blunt or the wrong type for what you are drilling.

Those three sound similar when you are stood there frustrated, but they need different answers, so it is worth the ten seconds to check.

Why bits slip inside the chuck

The chuck simply is not tight enough

This is by far the most common cause. Keyless chucks need a lot more force than most people give them. Hand tight with a quick twist is not enough for anything above about 6mm, especially in hardwood or metal where the bit grabs.

Grip the chuck sleeve firmly and turn it until you hear or feel the ratchet clicks, then keep going for another few clicks. On a two sleeve chuck, hold the rear collar and turn the front. Some people give the chuck a final nip by holding it and pulsing the trigger in reverse, but do this gently, and never on a drill without a proper ratcheting chuck.

The shank is round when it should be hex

Plain round shank bits rely entirely on friction. Under load they can twist inside the jaws no matter how tight you go. Hex shank bits have flats for the jaws to bite against and are far harder to spin loose, which is why most impact driver bits use them. If you are repeatedly losing grip on a big spade bit or hole saw, switching to a hex shank version usually ends the problem outright.

The jaws are worn, dirty or full of dust

Chuck jaws collect masonry dust, sawdust and metal swarf, and that debris stops them closing evenly. Open the chuck fully, point it downwards and blow it out with compressed air or brush it with an old toothbrush. A drop of light oil on the jaw threads, worked open and closed a few times then wiped off, brings a lot of sticky chucks back to life.

Worn jaws are a different story. If the gripping faces have gone smooth and rounded rather than sharp and ridged, they will never hold properly again and the chuck needs replacing.

The bit shank is damaged

Once a bit has slipped badly, the jaws chew grooves and burrs into the shank. Those burrs stop the jaws seating flat next time, so it slips more easily, which causes more damage. It becomes a loop. Run a file or a bit of emery cloth over the shank to knock the high spots off, or bin the bit if it is badly scored.

You are using the wrong bit for the chuck

SDS and SDS Plus bits have slots cut into the shank and are designed to move back and forth inside the tool. They will never hold securely in a standard keyless chuck. Likewise, do not force a bit that is too large for the chuck capacity, because part of the shank sitting outside the jaws means only a fraction of it is being gripped.

Keyed chucks need the key in all three holes

If your drill takes a chuck key, use it in every one of the three keyholes, not just the first one you reach. Tightening from one position only pulls the jaws unevenly and leaves the bit off centre. Tighten each hole in turn and the grip is noticeably better. And if the key has rounded off its teeth, replace it, because a worn key cannot apply proper force.

When the bit skates across the surface instead

If the bit is held fine but slides around before it bites, you are missing a starting point. On wood or metal, mark the spot with a centre punch to make a small dimple for the tip to sit in. On tile and glass, start at a shallow angle to cut through the glaze, then bring the drill upright once you have a groove. Masking tape over the drilling point gives the tip something to grab and stops it wandering on smooth surfaces.

Speed matters here too. Starting fast makes skating worse. Begin slowly with light pressure until the bit has cut a seat, then increase speed once it is anchored.

The bit turns but nothing happens

A blunt bit will polish a hole rather than cut it, and the heat that builds up hardens the material and makes it worse. If you are getting dust rather than shavings from wood, or nothing at all from steel, the bit has had it. Check you are also using the right type, because a wood bit will barely scratch masonry and a masonry bit will tear through timber badly.

Stopping it happening again

• Tighten the chuck properly every time, then check it again after the first few seconds of drilling
• Buy hex shank bits for anything large or high torque
• Blow the chuck out whenever you have been drilling masonry
• Let the bit cut at its own pace rather than leaning on the drill, since heavy pressure is what makes bits twist loose
• Retire scored or blunt bits instead of fighting them