A dull drill bit costs you money twice: once when you replace it too early, and again in wasted battery power and time because it’s not cutting efficiently. A sharp bit drills faster, stays cooler, and produces cleaner holes. If you drill regularly, learning to sharpen bits at home saves a lot of money and means you’re never caught mid-job with a blunt set.
Signs Your Drill Bits Need Sharpening
Before you even think about sharpening, make sure the bit is actually dull and not just the wrong type for the job. A dull bit shows these signs:
- Squealing sound — high-pitched squeal or screech means the edges aren’t cutting cleanly
- Smoking or burning smell — friction from a blunt edge generates heat; the wood scorches
- Needs excessive pressure — you have to lean hard on the drill to make progress; a sharp bit self-feeds
- Walks off centre — the bit drifts sideways instead of drilling straight; blunt edges lose tracking
- Produces dust instead of chips — fine sawdust means the edges are tearing, not cutting
- Hole has rough, torn edges — particularly visible on the exit side of hardwood
- Takes twice as long as it used to — the obvious one; you notice the slowness immediately
If your bits show any three of these signs, they need sharpening or replacing.
What You Can Sharpen vs What You Can’t
Not every bit type is worth sharpening. Some are designed to be thrown away, and trying to sharpen them wastes your time.
Can Sharpen — Worth the Effort
High-speed steel (HSS) bits — the standard silver/grey twist drills. These sharpen well and you’ll get good results.
Cobalt HSS bits — tougher than standard HSS, sharpens beautifully. If you’re doing a lot of metal drilling, these are worth sharpening.
Masonry bits — carbide-tipped masonry bits can be sharpened, but only on the carbide tip itself (not reshaping the whole bit). You need a diamond stone or diamond wheel, not a regular bench grinder.
Brad point bits — the spurred cutting edges sharpen well on a bench grinder with care.
Can’t Sharpen or Not Worth It
Titanium-coated bits — the gold/bronze coating is what makes them last, but once you sharpen it away, you’ve lost the benefit. The underlying steel dulls quickly after.
Carbide-tipped masonry bits on a standard grinder — a regular wheel will overheat and damage the carbide. You need specialist diamond equipment.
Spade bits (paddle bits) — these are made to be cheap and disposable. The geometry doesn’t sharpen cleanly; replace them instead.
Damaged or snapped bits — if the edge is chipped off or the tip is bent, it’s time for the bin. Trying to bring back a badly damaged bit usually creates an unsafe, imbalanced bit.
Badly worn bits — once a bit has worn past about 50% of its original diameter, the proportions are wrong and sharpening won’t restore its character. Replace it.
Method 1: Bench Grinder (Most Common)
A bench grinder is the most accessible way to sharpen bits at home. Most workshops have one, and they’re cheap if you don’t (£40–80 new). You’ll need:
- A bench grinder (electric; speed 3000–3600 rpm)
- A medium-grit wheel (60–80 grit)
- A water bucket for cooling (essential)
- Eye protection
- Steady hands and patience
The Technique
Step 1: Understand the angle. A general-purpose twist drill has a 118° included angle (the angle formed by the two cutting edges at the tip). This means each edge makes a 59° angle to the axis of the bit. You’re aiming to maintain this 59° on each side.
Step 2: Position the bit. Hold the bit in your hand, angled at roughly 59° to the grinding wheel. The flute (spiral groove) should point slightly upward so the edges engage the wheel, not the face of the flute.
Step 3: Make light passes. Touch the cutting edge to the wheel for a second at a time, using very light pressure. Make 2–3 light grinds on one edge, then switch to the other edge. The key is balance: both edges must be ground equally or the bit will walk.
Step 4: Cool constantly. After every 2–3 grinds, dip the bit tip in your water bucket. Don’t overheat — heat damages the steel’s temper (its hardness). If it turns blue or purple, you’ve overheated it and the edge will be soft.
Step 5: Check your work. After a few passes on each edge, stop and inspect. The grinding should have removed the worn flat edge from both sides and created a sharp, symmetrical point. Both edges should be the same length or the bit will be off-centre.
Step 6: Touch up the back rake. A tiny grind on the underside of each edge (the face behind the cutting edge) can improve performance. This is optional and needs practice, but it gives a smoother cut.
Common Mistakes
Grinding too aggressively. If you press hard, you’ll overheat the edge in seconds. Light, quick touches are far better than heavy pressure.
Not dipping in water. Once an edge turns blue from heat, it’s soften and won’t hold an edge well. Cool frequently.
Grinding unevenly. If you grind one edge twice as much as the other, the bit becomes lopsided and will walk. Count your passes and keep them equal.
Changing the angle dramatically. Stick to the 59° included angle. If you grind at a much steeper or shallower angle, the bit won’t cut correctly.
Using a coarse wheel. A very coarse wheel (36–40 grit) removes metal too fast and is hard to control. Use 60–80 grit; it’s gentler and easier to get a good finish.
Method 2: Drill Bit Sharpening Jig (Most Consistent)
If you sharpen bits regularly, a sharpening jig takes the guesswork out and produces the most consistent results. Common models are the Drill Doctor (rotary model) and generic handheld clamps.
A jig holds the bit at the exact correct angle and guides it into the wheel or stone. You just push and pull without worrying about angle or balance. Results are professional and repeatable.
How a Sharpening Jig Works
Most jigs have:
- A collet or chuck to hold the bit at a fixed angle
- A built-in grinding wheel or diamond stone
- A guide rail so you push the bit toward the stone in the same way each time
- Stops to limit how far you can grind (prevents over-sharpening)
Insert the bit, tighten the collet, and push it forward toward the stone 5–10 times. The jig handles the angle and ensures both edges are ground equally. Results are fast and much more consistent than freehand grinding.
Jigs are worth the investment (£30–70) if you sharpen more than a dozen bits per year. For casual home use, a bench grinder is fine.
Method 3: Diamond File (Quick Touch-Ups Only)
If you’re on a job site and a bit has just dulled, you can do a quick touch-up with a diamond file without needing a grinder. This won’t fully resharpen a badly worn bit, but it can restore a recently dulled edge enough to get you through the job.
The technique: Hold the bit in a vice and carefully stroke a diamond file across each cutting edge 2–3 times, maintaining the 59° angle as best you can. This is rough and requires practice, but it works in an emergency.
Diamond files are cheap (£3–5) and small enough to fit a toolbag. Not a replacement for proper sharpening, but useful on site.
Sharpening Masonry Bits (Carbide-Tipped)
Carbide-tipped masonry bits are harder than steel and can’t be sharpened on a regular bench grinder. You need a diamond stone or diamond wheel.
Method: Diamond Stone or Diamond Wheel
A diamond stone (or diamond hone) has tiny diamonds embedded in the surface. You hold the masonry bit against it and make light passes, just like sharpening a knife on a whetstone.
Work slowly and carefully. You’re only sharpening the carbide tip itself, not reshaping the whole bit. A few light strokes on each side of the tip is enough.
This is specialist work and requires experience. If you’re not confident, take badly dulled masonry bits to a trade tool sharpening service — they have the equipment and know-how.
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Testing Your Sharpened Bit
After sharpening, test the bit before trusting it on an important job:
The scrap wood test: Drill a hole in a scrap of hardwood. A sharp bit should:
- Self-feed without excessive pressure
- Produce spiral chips, not dust
- Drill straight without walking
- Stay cool to the touch
- Produce a clean hole with no tearout
If the bit produces dust, needs excessive pressure, or overheats, it’s not sharp enough. Go back to the grinder for another touch-up.
The visual check: Look at the cutting edges under good light. They should be shiny and sharp, not dull or rounded. If you see a flat spot on the edge, you need more grinding.
When to Replace Instead of Sharpen
Sometimes a replacement is better than sharpening:
- Bits less than 2mm diameter — too fragile to sharpen safely by hand
- Heavily damaged or snapped bits — reshaping won’t restore them
- Bits that have worn to less than 50% of original diameter — geometry is too compromised
- Bits you haven’t sharpened in 2+ years — they’ve dulled from storage wear too
- Cheap disposable bits — they cost less than 30p; replacement is faster
New bits are cheap. If sharpening takes 10 minutes and the bit costs 50p, you’re spending your time to save pocket change. For expensive bits (quality cobalt or specialist types), sharpening is worth it.
Watch: Video Guide
Frequently Asked Questions
How Often Should You Sharpen Bits?
Every 10–20 holes in hardwood, or when you notice the signs (squealing, smoke, slow drilling). In softwood, bits last longer. With metal drilling, sharpen after every 5–10 holes if you’re being serious. For home use, sharpen once per year or when needed.
Can You Over-Sharpen a Drill Bit?
Yes. If you grind away too much metal, the bit becomes too small and weak. Light passes are better than aggressive grinding. If you’re unsure, stop and test on scrap wood before grinding more.
What Angle Should You Use?
For general-purpose bits, 59° on each side (118° included angle). For metal drilling, some people use 135° (67.5° on each side) for harder metals. For wood, stick to 118°. If you’re using a jig, it handles the angle for you.
Can You Sharpen Brad Point Bits?
Yes, but carefully. The centre point and spurs need to be maintained at the same height or the bit won’t self-centre. A sharpening jig is better than freehand for brad point bits.
What’s the Difference Between HSS and Cobalt?
Cobalt is tougher and lasts longer, especially in metal. Both sharpen the same way. Cobalt bits are more expensive but are worth it if you drill metal regularly.
Is It Safe to Use a Bench Grinder for Sharpening?
Yes, if you follow basic safety rules: wear eye protection, keep your fingers clear of the spinning wheel, never reach over a spinning wheel, and let the grinder stop completely before removing the bit. A bench grinder is the safe way to sharpen — much safer than trying to file by hand.
How Long Does a Sharpened Bit Last?
Just as long as the original. The metal hasn’t changed, only the edge shape. With good technique, a sharpened bit performs as well as a new one. You can sharpen a bit 5–10 times before the metal becomes too small or weak.
