How to Sharpen Drill Bits with a Rotary Tool: Save Money, Sharpen Like a Pro
Signs Your Drill Bit Needs Sharpening
| Symptom | What's Happening |
|---|---|
| A bit wanders or "walks" across the surface before biting | The cutting edge is rounded—it can't center itself |
| Drilling takes much longer than it used to | You're rubbing, not cutting. The bit is dull. |
| Smoke or burning smell from wood | Friction from a dull bit generates excessive heat |
| Metal chips are dust, not curly shavings | Sharp bits produce clean curls; dull bits produce powder |
| Chuck slips or bit spins in the drill | Excessive pressure from pushing a dull bit |
| The hole is larger than the bit size | A wobbling dull bit reams out an oversized hole |
Drill Bit Anatomy (What You're Sharpening)
Understanding the parts of a drill bit makes sharpening intuitive. You're restoring two things:
- The cutting edge — the sharp lip that actually cuts the material
- The relief angle — the slope behind the cutting edge that prevents the bit from rubbing
The goal: both cutting edges must be identical in length and angle. An asymmetrical bit drills an oversized, crooked hole.
Tools & Accessories Needed
- Rotary tool with variable speed—the Hardell 200W with Flex Shaft is ideal; the flex shaft gives precise angle control
- Aluminum oxide grinding stone (pink or orange) — cylindrical or cone-shaped. Included in the Hardell 180W kit and 230-piece kit
- Diamond grinding bit (optional) — for carbide and masonry bits
- Bench vise or clamp — to hold the bit steady while you work
- Permanent marker — to mark the cutting edge before grinding
- Safety glasses — metal sparks and grinding dust
Step-by-Step: How to Sharpen a Drill Bit
- Secure the bit. Clamp the drill bit in a bench vise with the tip pointing up and slightly toward you. The cutting edge you're sharpening should be at the top, facing you.
- Mark the cutting edge. Color the entire cutting lip with a permanent marker—this shows you where you're grinding.
- Mount the grinding stone. Use an aluminum oxide grinding stone (pink/orange) in your rotary tool. Set speed to 15,000–20,000 RPM.
- Match the angle. Hold the grinding stone against the cutting edge at a 59-degree angle (for standard 118-degree bits). The stone should contact only the cutting edge and the relief behind it—not the entire bit face.
- Grind with light pressure. Make 3–4 light passes along the cutting edge. Watch the marker disappear. Do not dwell in one spot—you'll overheat the bit and ruin the temper (blue discoloration = softened steel).
- Cool the bit. Dip in water after every 3–4 passes. If the bit turns blue, you've overheated it—that section is now soft and won't hold an edge.
- Match the other side. Flip the bit and sharpen the opposite cutting edge the same way. Count your passes — both sides need the same number for symmetry.
- Check symmetry. Hold the bit tip-up and compare both cutting edges. They should be equal length and meet at the same angle. If one is longer, grind it slightly more.
- Test the bit. Drill into a piece of scrap wood or metal. A sharp bit should bite immediately, produce clean curls (metal) or chips (wood), and drill without excessive pressure.
Correct Sharpening Angles by Bit Type
| Bit Type | Point Angle | Material It's For | Grinding Stone |
|---|---|---|---|
| Standard Twist (118°) | 118° (59° per side) | Wood, plastic, mild steel, general purpose | Aluminum oxide (pink) |
| Split-Point (135°) | 135° (67.5° per side) | Hard steel, stainless steel, hard metals | Aluminum oxide or diamond |
| Brad Point (wood) | Center point + outer spurs | Wood only—clean holes, no tear-out | Aluminum oxide (cone shape) |
| Masonry Bit | 135° carbide tip | Brick, concrete, stone | Diamond bit ONLY—aluminum oxide won't cut carbide |
Sharpening Different Types of Bits
Standard Twist Bits (HSS — High-Speed Steel)
These are the most common bits—the ones in every drill bit set. Use an aluminum oxide grinding stone at 15,000–20,000 RPM. Follow the step-by-step above. With practice, you'll sharpen a bit in under 60 seconds. The Hardell 200W, with its fine speed control, is perfect for maintaining a consistent angle.
Split-Point Bits (135°)
These have a notched center that self-centers — no center punch needed. Sharpening is trickier because you must preserve the split point. Use a cone-shaped grinding stone at 15,000 RPM. Sharpen each cutting edge at 67.5°, then lightly touch up the split point notch with a small diamond burr. The Hardell 230-piece kit includes the small diamond burrs you need.
Masonry Bits (Carbide-Tipped)
The tip is carbide—extremely hard but brittle. You MUST use a diamond grinding bit—aluminum oxide stones won't touch carbide. Use light pressure at 10,000–15,000 RPM. Overheating carbide can cause microcracks. Sharpen only the carbide tip, not the steel body.
Brad Point (Wood) Bits
These have a center spur and outer cutting spurs. Sharpen the center point first (like a standard bit), then carefully touch up the outer spurs with a small cone stone. The outer spurs do the clean cutting — they must be sharp and even. The Hardell 8V cordless at low speed is ideal for delicate outer spur work.
How to Test If Your Bit Is Sharp
- The thumbnail test: Gently drag the cutting edge across your thumbnail at a shallow angle. A sharp bit catches immediately; a dull bit slides.
- The drill test: Drill into scrap material. A sharp bit starts cutting instantly with light pressure. It produces clean spirals (metal) or chips (wood), not dust.
- The light test: Hold the bit under a bright light and rotate it. A sharp cutting edge reflects no light — it should be a crisp, dark line. If you see a shiny rounded edge, it's dull.
Common Sharpening Mistakes
| Mistake | Result | How to Avoid |
|---|---|---|
| Unequal cutting edges | Oversized, crooked holes; bit wanders | Count passes on each side. Check symmetry after every 3–4 passes. |
| Overheating (blue discoloration) | Steel loses temper and won't hold an edge. | Dip in water every 3–4 passes. Light pressure. If it turns blue, grind past the blue area. |
| Wrong angle | Bit won't cut; skips across surface | Match the original angle. 118° (59° per side) for general-purpose bits. |
| No relief angle | Bits rub instead of cutting; friction heat | Grind slightly behind the cutting edge to create clearance. The cutting edge must be the highest point. |
| Using wrong grinding stone | No material removal or damaged bit | Aluminum oxide for HSS. Diamond for carbide. Never use aluminum oxide on carbide—it won't work. |
Frequently Asked Questions
Q: Can you really sharpen drill bits with a rotary tool?
A: Yes — and it works well for bits up to about 3/8" (10mm). Beyond that, a bench grinder is more practical. For the most common sizes (1/16" to 3/8"), a rotary tool with an aluminum oxide grinding stone does an excellent job. The Hardell 200W has the power and speed control needed.
Q: How often should I sharpen drill bits?
A: Sharpen when you notice the signs: wandering, slow drilling, burning smell, dust instead of chips. For a home DIYer, that's typically every 20–50 holes in metal, or every 100+ holes in wood. Professionals may sharpen daily.
Q: What speed should I use to sharpen drill bits?
A: 15,000–20,000 RPM for HSS bits with aluminum oxide stones. 10,000–15,000 RPM for carbide bits with diamond stones. Lower speed = less heat = less chance of ruining the temper.
Q: Can I sharpen cobalt- or titanium-coated bits?
A: Yes, but you'll remove the coating from the sharpened area. Cobalt and titanium coatings are surface treatments — once you grind through them, the underlying HSS steel is exposed. The bit will still cut but won't have the coating's wear resistance on the cutting edge. Sharpen sparingly.
Q: When should I just replace a drill bit instead of sharpening?
A: Replace if the bit is visibly bent, the tip is broken off, the bit is under 1/16" (too small to sharpen accurately), or you've sharpened it so many times the flutes are short. For most bits, sharpening extends life by 5–10x before replacement.
Stop throwing away dull drill bits. With a Hardell 200W Rotary Tool and the right grinding stones (included in the 230-piece accessory kit), you can sharpen bits in under 2 minutes and save hundreds on replacements. Browse the full collection to find the right tool.
