Drill bits break. Sometimes it’s bad luck, but most often it’s technique or material mismatch. A snapped bit is frustrating enough, but worse is the risk of the broken piece flying out or jamming your drill. This guide tells you why they break and, more importantly, how to stop it happening.
The Top 10 Reasons Drill Bits Break
1. Using the Wrong Bit Type for the Material
This is the most common cause. A wood bit in masonry is destroyed on first contact. The sharp steel edges chip off instantly and the bit tries to grind its way through with blunt edges, binds up, and snaps.
Conversely, a masonry bit in wood isn’t designed to cut cleanly — it smashes the grain, the bit doesn’t progress, and you lean harder, causing the bit to snap under sideways pressure.
Fix: Use the correct bit type. Masonry bits for masonry, wood bits for wood, metal bits for metal. A few seconds checking the bit is cheaper than replacing it.
2. Running Speed Too High
Every material has an ideal drilling speed. Run too fast and the friction and heat cause the edge to soften (lose temper) and the metal becomes brittle. A brittle edge snaps under the smallest sideways load.
Metal drilling is the most speed-sensitive. A small HSS bit in steel should run at 1000–2000 rpm depending on diameter. Run it at 3000 rpm and the edge heats up, softens, and breaks.
Large-diameter bits in wood also break from excessive speed. The faster you spin a 15mm bit, the more vibration and the greater the risk of a sudden sideways snap.
Fix: Use a cordless drill with variable speed and dial it down for metal and large-diameter work. The general rule: slower for harder materials and larger bits, faster for soft materials and small bits.
3. Excessive Downward Pressure
The biggest mistake. Many people think “more pressure = faster drilling.” Wrong. More pressure overloads the cutting edge, generates excessive heat, and bends the bit.
A sharp bit self-feeds. You should barely need to lean on the drill at all — it cuts because the edge is sharp, not because you’re forcing it. As soon as you lean hard, you’re fighting the bit instead of letting it work.
Fix: Let the bit do the work. Touch down with light-to-moderate pressure and let the rotation do the cutting. If you’re pressing hard, either the bit is blunt (sharpen it), the speed is wrong (adjust it), or the material is unexpected (check what you’re drilling).
4. No Pilot Hole for Large Diameter Bits
A 10mm or larger bit needs a pilot hole to start. Without it, the bit wanders or jumps, and you fight to keep it centred. That fight = sideways pressure = bent or broken bit.
A small pilot hole (2–3mm) lets the large bit start calmly and cut straight. The initial position is established and the bit can then do its job without trying to correct course constantly.
Fix: Drill a small pilot hole first. Takes 10 seconds, saves bits, and produces straighter holes. Especially critical for hardwood and metal.
5. Bit Walking or Centre-Drift
On smooth or slippery surfaces (polished metal, plastic, tile), a bit can wander instead of starting a hole. It skates across the surface, then suddenly catches and either digs in too hard or bends.
Wood is less prone to this because the rough surface grabs the bit naturally. Metal and tile are the culprits.
Fix: Use a centre punch to make a small dimple at the drilling point. The bit’s point drops into the dimple and can’t wander. A one-second tap with a centre punch and hammer saves a snapped bit.
6. Sideways Pressure or Leverage
This is where bits snap catastrophically. If you’re holding the drill and sideways force is applied (the workpiece rotates, the bit binds and twists, or you’re leaning on the drill handle laterally), the bit bends and snaps.
Hole saws are particularly prone to this. A large-diameter hole saw binds, the workpiece suddenly rotates, and if your grip is weak, the drill torque snaps the saw or the arbour.
Fix: Secure the workpiece firmly. Use a clamp or vice so it can’t rotate. Hold the drill with both hands, keeping the handle aligned with the bit. Expect sudden torque from large-diameter bits and be ready for it.
7. Blunt or Dulled Bit
A dull bit works slower and generates more heat. You subconsciously lean harder to make progress. The heat softens the edge, pressure bends it, and snap. Blunt bits also bind in the hole more, creating a jam-and-snap situation.
This is preventable through regular sharpening or timely replacement.
Fix: Keep bits sharp. A sharp bit self-feeds at normal speed. If a bit is working hard, stop and sharpen it or use a fresh one. Don’t keep drilling with a dull bit and hoping it’ll free up.
8. Overheating (No Cooling or Lubrication)
Metal drilling generates serious heat. Without cooling (oil or cutting fluid), the bit edge heats up and loses temper (becomes soft and brittle). Once soft, any pressure causes it to bend or break.
In metal, you should be using cutting oil. A drop of 3-in-1 oil on the bit every few seconds keeps it cool and reduces friction.
Even in wood, excessive friction (blunt bit, wrong speed) can generate enough heat to soften the edge slightly and increase the risk of snapping.
Fix: Use cutting oil for metal drilling. Work at the correct speed so friction is minimized. For wood, don’t force dull bits — sharpen or replace them.
9. Hitting Hidden Obstacles
You’re drilling a hole in what you think is solid wood, and suddenly the bit hits a nail, screw, or knot. The sudden resistance jams the bit and it snaps.
In concrete, hitting rebar or a hidden void stops the bit suddenly. Same result: sudden jam = snapped bit.
Fix: Before drilling, check for fasteners using a stud finder or metal detector. Tap with a hammer and listen for hollow sounds (voids). In old plaster walls, go slowly and listen for changes in sound. Once you hit something hard, stop and investigate before continuing.
10. Cheap, Low-Quality Bits
Budget bits are made with cheaper steel and weaker metallurgy. They break more easily under stress because they’re not designed to the same tolerances as quality bits.
This isn’t always a reason to blame the bit — poor technique will break any bit. But cheap bits have a lower safety margin. Questionable angle ground in, inconsistent hardness, poor material.
Fix: Buy quality bits from established brands (Bosch, Makita, DeWalt, Irwin). They cost slightly more but last dramatically longer and are less prone to breaking. A £0.80 quality bit beats a £0.25 budget bit.
Material-Specific Prevention Tips
| Material | Best Bit Type | Speed | Key Prevention |
|---|---|---|---|
| Softwood | Brad point or twist drill | 1500–2500 rpm | Use light pressure. Pilot hole for large bits. Keep sharp. |
| Hardwood | Brad point, twist drill, or Forstner | 800–1500 rpm | Pilot hole essential for anything over 6mm. Centre punch. Go steady. |
| Plywood | Twist drill or Forstner | 1000–2000 rpm | Back with scrap board to prevent tearout. Watch for veneers splitting. |
| Plastic | Twist drill or spade bit | 1500–2500 rpm (slower for thick) | Slow entry to prevent cracking. Centre punch first. Watch for heat melt. |
| Mild steel | HSS or cobalt | 500–1500 rpm (smaller = faster) | Use cutting oil. Pilot hole. Secure workpiece. Go slow. |
| Stainless steel | Cobalt or special stainless bit | 300–800 rpm | Oil essential. Very slow. Can stick suddenly — be ready for it. |
| Aluminium | HSS twist drill | 1500–3000 rpm | Can bind suddenly. Secure it. Expect torque. Don’t lean hard. |
| Brick | Masonry bit (carbide-tipped) | 500–1000 rpm + hammer | Use hammer function. Light pressure. Let the hammer work. Cool regularly. |
| Concrete | SDS masonry or TCT bit | 400–800 rpm + hammer | SDS rotary hammer best. Standard drill will struggle. Watch for rebar. |
| Tile/Glass | Diamond hole saw or glass bit | 200–500 rpm | Water cooling essential. Slow and steady. Tape on entry side prevents chip. |
When Breaking Is the Material’s Fault (Not Yours)
Sometimes a bit breaks and there’s nothing you could have done differently:
Hidden rebar in concrete: You’re drilling what appears to be a small hole in concrete, the bit hits rebar, and snaps instantly. This is unpreventable short of X-raying the wall. Metal detectors sometimes find it, sometimes don’t.
Hidden knots or dead wood in old timber: A knot is as hard as bone. If a bit hits it at the wrong angle, it can snap.
Voids in masonry (cavities, air pockets): You’re drilling brick and suddenly there’s an air pocket. The bit drops through and jams on the other side.
Sudden material change (backing concrete behind plaster): Drilling what you think is pure plaster, and suddenly the bit hits concrete behind it with no warning.
These are the luck-of-the-draw breaks. They happen even with perfect technique. Keep spare bits on hand for these situations.
Cost of Prevention vs Replacement
Let’s talk money: a quality 8mm twist drill costs about 60p. A centre punch costs £3 once. A portable drill vice for secure clamping costs £15–20.
If using a centre punch prevents one broken bit per week, you’ve paid back that £3 in a month. If a drill vice stops you destroying two bits per job, it pays for itself in two jobs.
Sharpening equipment (bench grinder £50, or sharpening jig £40) pays back in about 100 bits sharpened instead of replaced.
Prevention is always cheaper than replacement, both in cost and frustration.
What To Do When a Bit Breaks
If it breaks in the hole: Stop drilling. Don’t try to punch the broken piece out with another bit — you’ll just snap more bits. Use a small screw or extractor tool to carefully remove the broken piece. Or carefully reverse-spin a slightly larger bit around the edge to grind away the broken piece.
If it breaks in your hand: You’ve got a sharp, jagged piece of metal. Wear gloves and handle carefully. File or grind the sharp edge smooth before disposing of it.
If it snaps suddenly and flies: This is rare but dramatic. It’s why eye protection is non-negotiable. A flying bit piece is sharp and travels fast.
Afterward: Think about what went wrong. Was it pressure, speed, the material, or a hidden obstacle? Apply the fix so it doesn’t happen again.
Choosing Bits To Minimise Breakage
Quality matters:
- For general DIY: Bosch or DeWalt 13-piece wood bit sets (£5–8). They’re reliable and less prone to breaking.
- For metal work: Cobalt bits (£1–2 per bit). They’re tough and handle speed and pressure variations better than basic HSS.
- For masonry: Named-brand carbide-tipped bits (Bosch, DeWalt). Cheap masonry bits are gritty and snap more easily.
- For occasional use: A mixed 16-piece set covers most jobs and is cheaper than buying specialty bits.
Buy Bosch wood bit set on Amazon
Buy cobalt metal bit set on Amazon
Buy carbide masonry bit set on Amazon
Watch: Video Guide
Frequently Asked Questions
Can You Fix a Bent Drill Bit?
Not really. A bent bit won’t drill straight and is too weak to use safely. Trying to straighten it by heating and bending by hand will weaken the metal further. It’s time for the bin.
What Speed Should You Use for Metal?
The smaller the bit, the faster the speed. A 2mm bit in steel: 3000 rpm. A 10mm bit: 800 rpm. A 20mm bit: 400 rpm. As a rough rule: smaller = faster, larger = slower. Always use cutting oil with metal.
Why Do Bits Break in Concrete?
Concrete is hard and unforgiving. Hidden rebar, voids, or dense aggregate can jam a bit suddenly. Use a dedicated rotary hammer with SDS bits for concrete — a cordless drill will struggle and bits are more likely to snap. Go slow and expect resistance.
Is Sideways Pressure Really That Dangerous?
Yes. Sideways force on a thin bit (especially large-diameter bits) can bend it or cause sudden binding that snaps it. Secure your workpiece so it can’t rotate and hold the drill with both hands in a comfortable stance where you can’t apply accidental sideways leverage.
Should You Use Oil When Drilling Wood?
Not necessary for most wood, but it helps with hardwoods and large-diameter bits. It cools the bit slightly and reduces friction. Not critical like it is with metal.
How Do You Know If a Bit Has Lost Its Temper?
A bit that’s been overheated (turned blue from heat) feels slightly softer and snaps more easily than before. You can’t really tell by looking after it cools. The damage is done — the bit is now more brittle. Replace it or use it only for non-critical work.
