Learn How to Sharpen a Drill Bit: proper instructions

Sharpening a twist drill bit restores cutting edges that are dull but otherwise sound. It is a worthwhile skill for ordinary high-speed steel (HSS) twist bits used in wood, plastic and mild steel. It is not a way to rescue every bit. Replace cracked, badly burnt, heavily rusted, bent or undersized bits, and do not hand-sharpen masonry bits, spade bits, hole saws, step bits, carbide-tipped bits or brad-point bits using this general method. Those types have different geometry and often need a dedicated sharpener or replacement.

Safety boundary

Use a stable bench grinder with intact wheel guards, tool rest and eye shields, or a purpose-made drill-bit sharpener. Wear safety glasses or a face shield, close-fitting clothing and hearing protection as appropriate. Tie back long hair and remove loose jewellery. Never use gloves close to a rotating grinding wheel; they can catch. Do not grind on the wheel’s side unless the wheel is specifically rated for it. Stand slightly to one side when starting the grinder, let it reach speed and reject a wheel that wobbles, is damaged or lacks guards. Keep a container of water nearby for cooling the bit, but never quench a red-hot bit; overheating can ruin temper and sudden cooling can stress it.

Tools and setup

• Bench grinder with a fine, dressed wheel, or a drill-bit sharpening jig/sharpener.
• HSS twist drill bits only, cleaned so the edges are visible.
• Safety glasses, ruler and marker pen.
• Good task light and a magnifier if available.
• Water container for frequent cooling.
• Scrap softwood and, for metal-bit testing, thin mild steel clamped securely.
• Drill press or hand drill, clamps and appropriate cutting fluid for metal.

Understand the anatomy before grinding. At the tip are two cutting lips meeting at a central chisel edge. Behind each lip is a relieved surface that must fall away so the lip, not the heel, contacts the work. Many general-purpose bits use an included point angle around 118 degrees; harder materials often use a flatter point around 135 degrees. For learning, restore the existing general-purpose angle rather than trying to redesign it. The two lips must be equal in length and angle or the bit will cut oversize, wander or drill poorly.

Numbered action

1. Clean and inspect the bit. Roll it on a flat surface to check for obvious bend. Look for chipped lips, blue discolouration at the tip, a broken web or severe corrosion. Discard the bit if damage extends well beyond the tip or if it cannot be made symmetrical without removing too much material.
2. Set the grinder tool rest close to the wheel, with the gap small enough that the bit cannot be pulled into it. Check the wheel is dressed and running true. Put on eye protection, start the grinder and allow it to reach full speed while standing clear of the direct plane of the wheel.
3. Hold the bit by its shank in your dominant hand, with the tip supported by the other hand. Present one cutting lip to the wheel at approximately the original point angle. The lip should be horizontal or slightly raised at its outer edge; do not aim the chisel edge straight into the wheel.
4. Touch the lip to the wheel very lightly for one or two seconds. While maintaining the angle, rotate the shank slightly and lower the rear of the bit a little. This rolling-and-lifting movement creates clearance behind the lip. Use gentle pressure: grinding should remove a small bright facet, not generate a shower of sparks or change the colour of the steel.
5. Remove the bit and cool it in water once it is warm. Inspect the facet. The cutting edge must remain at the outside, with relief descending behind it. If the heel is higher than the cutting edge, the bit will rub rather than cut; correct it with a light repeat pass that lowers the rear slightly more.
6. Grind the opposite lip using the same duration, position and motion. Alternate sides frequently instead of finishing one side completely. This is the best way to preserve symmetry and avoid grinding one lip much shorter than the other.
7. Inspect the point under strong light. The chisel edge should be centred, the lips should look equal, and the outer corners should be intact. Measure lip lengths from the chisel edge to each outer corner with a ruler or compare against a straight reference. Make tiny corrective passes only where needed.
8. Cool the bit fully, then remove only a light burr if present. Do not round over the cutting edges with a file or abrasive pad. A sharp drill edge is a crisp intersection, not a polished blunt curve.
9. Mark the bit if you altered its geometry substantially, then return it to its index or storage tube. Keep sharpened bits protected so their tips cannot knock together.

Testing and inspection

Clamp a piece of scrap softwood and drill a pilot-free test hole at moderate speed. The bit should begin cutting with modest pressure, produce even chips and make a round hole without skating excessively. Inspect the hole entrance and the chips. A bit with unequal lips may make an oversized or triangular-feeling hole, pull to one side or leave one lip doing all the cutting. For an HSS bit intended for mild steel, clamp thin mild steel securely, use a suitable cutting fluid and run at a low speed. It should make chips rather than only polishing the surface. Never hold metal by hand during a drill test.

After the test, inspect the tip again. Straw or blue colour indicates excessive heat; let the bit cool more often and use lighter contact next time. A dull-looking line at one outer corner often means that corner was not brought to the wheel equally. If repeated light corrections cannot create equal lips and correct relief, discard the bit. The cost of a replacement is lower than the risk of a broken bit, damaged workpiece or snapped drill.

Common mistakes

• Grinding one lip for much longer than the other and moving the chisel edge off-centre.
• Holding the bit still against the wheel, producing no relief behind the edge.
• Overheating the steel until it turns blue, which can reduce hardness at the cutting edge.
• Using heavy pressure, which gouges the point and makes consistent geometry difficult.
• Trying to sharpen carbide or masonry bits as if they were HSS twist bits.
• Testing in loose material or holding the test piece by hand.
• Continuing to use a bit that chatters, binds or produces an oversized hole.

When replacement is the correct repair

Replace the bit when the shank is damaged, the flutes are deeply corroded, the tip has multiple chips, the bit is bent, or you need precision holes beyond what you can verify. Use a drill-sharpening jig if you need repeatable geometry across many bits. The goal is not merely a pointed tip: it is two equal cutting lips with correct clearance, tested safely in clamped scrap material.