Drill bit sharpening, without the guesswork

A dull twist bit announces itself: it stops cutting and starts polishing, the hole takes forever and comes out oversize or scorched, chips come off one flute only, and the bit walks on the start. Sharpening fixes all of that, and the skill reduces to two angles held symmetrically: the point angle and the lip relief. This page covers the geometry, the angle chart by material, the freehand bench grinder method, the jigs and gauges that remove the freehand part of that sentence, and the honest cases where you should replace the bit instead.

The two angles that matter

Point angle is the included angle between the two cutting lips, seen head-on. Lip relief (also called clearance) is the angle ground behind each lip so the heel slopes away and the edge, not the heel, contacts the work; with no relief the bit rubs and polishes instead of cutting. Four independent references agree on the standard numbers: Zhonghuan Tools' sharpening guide, Teng Tools' drill bit angle guide, Hods' sharpening walkthrough, and Cutwel's sharpening guide.

• 118 degrees is the standard general-purpose point on ordinary HSS jobber bits: keen, easy-starting, right for wood, plastics, aluminum, and mild steel. Ground at half the included angle, which is 59 degrees per side.
• 135 degrees is the flatter point used on harder work: stainless, tool steel, tough alloys. Usually supplied as a split point, a thinned web that eliminates the dead chisel edge at the center, so the bit self-centers without a pilot hole and needs less thrust.
• Lip relief runs about 7 to 12 degrees behind each cutting edge; Engineer Fix quotes 12 to 15 as the range to aim for freehand. The cutting edge must be the highest point of the tip; if the heel touches first, there is no relief and no cutting.
• Match the original angle. The one universal instruction: do not convert a 135 degree bit to 118 or the reverse. Restore the geometry the bit was made with.

Both angles matter for a second reason: symmetry. If the two lips are different lengths, the bit spins about a center offset from its axis and cuts a hole bigger than its nominal size, sometimes by a surprising margin, a failure mode Teng Tools documents precisely. If the lips are equal length but different angles, only one lip cuts, the bit runs hot on one side, and edge life collapses. Both faults are easy to create freehand and easy to check with a gauge.

Freehand on a bench grinder

The traditional method, with the setup details from Hods and Engineer Fix's step-by-step, which agree with the Zhonghuan guide:

1. Set up the grinder. A 6 in bench grinder with an aluminum oxide wheel; Hods suggests fine 80 to 120 grit for a finishing pass, Zhonghuan 60 grit for stock removal. Dress the wheel flat if it is grooved. Set the tool rest so the bit meets the wheel face at 59 degrees to the centerline for a 118 degree point (half the included angle, per side).
2. Grip for control. Hold the shank near the back with your dominant hand and steady the flute near the point with the other; gloves off, eye protection on.
3. Grind one lip. Touch the lip to the wheel lightly, then in one motion rotate the bit clockwise 15 to 20 degrees while dropping the shank slightly. That combined movement is what creates the relief behind the edge. Two to three light passes maximum, then swap sides.
4. Alternate sides equally. Same number of passes, same pressure, same angle, each side. This is the whole discipline: unequal work per side is what makes oversize holes.
5. Keep it cool. Dip in water every few passes. If the tip turns blue or straw colored the HSS has lost its temper; you must grind back past the discoloration or the edge will not hold.
6. Check symmetry before testing. The head-on view should show equal lip lengths and the web (chisel edge) centered. Fix small errors by taking a pass off the longer lip only.
7. Test on scrap. A correctly sharpened bit starts cutting immediately with light pressure, no skating, no squeal, and chips come off both flutes evenly. Burrs from grinding come off with a few strokes of a honing stone along the flutes, per Cutwel.

Learn on a big bit: 3/8 in and up shows you the geometry while you work; tiny bits hide everything.

Jigs, guides, attachments, and gauges

The freehand method's hard part is repeating the same compound motion identically on both lips. The tooling that solves it:

• Sharpening jigs and guides clamp the bit at a set angle and present it to the wheel in a controlled slide, replacing muscle memory with a mechanical stop. Zhonghuan's summary of their value is fair: they produce consistent geometry without the skill, at the cost of setup time.
• Dedicated sharpening machines and attachments take it further: the best-known category example is the Drill Doctor line, which Hods reviews at 100 to 130 dollars for the 750X model, sharpening 3/32 to 3/4 in bits in about 30 seconds each and grinding both the point and a split point. Zhonghuan's break-even guidance: dedicated machines pay off around 20 or more bits per month.
• Sharpening gauges are the cheap half of the solution: angle templates and lip-length gauges that tell you what your eyes cannot, whether the point angle is actually 118 and the lips are actually equal. Checking with a gauge instead of by eye is the difference between a sharpened bit and a slightly rounder dull one.

A middle path costs nothing: a bench grinder plus a printed angle template and a drill gauge for checking. That covers occasional sharpening well; the powered jigs earn their shelf space at volume.

When to sharpen, when to replace

• Sharpen: plain uncoated HSS twist bits, the workshop workhorses. Cobalt bits sharpen fine too and are worth the effort especially at larger diameters (Zhonghuan's cutoff: 12 mm and up).
• Replace instead: carbide-tipped spear-point tile bits, which are not practically resharpened; masonry bits whose brazed carbide tip is chipped; and any bit that has snapped, gone blue from overheating past what you can grind out, or lost so much length that flute depth no longer clears chips.
• Sharpen the moment cutting degrades, not when the bit is fully dead: waiting multiplies heat damage to the margins and shortens total life, per Cutwel.

Bit families and their trade-offs (HSS versus cobalt versus carbide, and which drills each suits) are covered in our drill bits by material guide; this page is about recovering the edge you already own.

Quick answers

• What angle do you sharpen a drill bit? Match the original: 118 degrees for general-purpose HSS bits, 135 degrees (usually split point) for bits made for stainless and hard alloys. Half the included angle per side: 59 degrees to the wheel face for 118.
• Can you sharpen drill bits with a bench grinder? Yes; it is the standard method. Light passes, alternate sides equally, dip in water, and check symmetry with a gauge rather than by eye.
• Is a sharpening jig worth it? For occasional bits, a gauge plus careful freehand is enough. At volume (roughly 20+ bits a month) a dedicated sharpener like a Drill Doctor pays for itself in consistency.
• Why does my sharpened bit drill oversize holes? Unequal lip lengths: the bit spins off-axis. Take a light pass off the longer lip until the head-on view shows equal lips and a centered web.
• Can masonry and tile bits be sharpened? Masonry bits can be touched up on a bench grinder (carbide tips tolerate it). Spear-point tile bits effectively cannot; replace them.

Related guides

Also on this site: drill bits by material for choosing the bit in the first place, specs explained for what the drill itself contributes to the cut, and torque settings explained for feeding the edge properly once it is sharp.