How to Sharpen Drill Bits: By Hand and With a Jig
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A dull drill bit generates heat instead of chips. It wanders off center, squeals, and takes forever to punch through. Throwing it away and grabbing a new one works, but a $1 bit sharpened in 30 seconds on a bench grinder is back to cutting like new. The skill isn't hard. The geometry is just two facets meeting at a 118-degree point. Once you understand what you're trying to create, the grinding takes less time than finding the right size bit in the case.
How Drill Bit Geometry Works
A standard twist drill bit has two cutting edges (lips) that meet at a chisel point in the center. Each lip is ground at a 59-degree angle from the axis, which creates the standard 118-degree included point angle (59 + 59). Behind each lip, a relief angle (typically 8 to 12 degrees) keeps the heel of the lip from rubbing against the bottom of the hole. If there's no relief, the bit skates instead of cutting.
The chisel point at the center doesn't cut. It pushes material aside. That's why drill bits need downward pressure to start. Split-point bits have a notch ground into the chisel edge that creates a small cutting edge at the center, which is why they self-center and start faster. Most fresh bits from the factory are split-point. Resharpening by hand restores the lips but not the split, so hand-sharpened bits may need a center punch to start cleanly.
Freehand Sharpening on a Bench Grinder
Set the tool rest on your bench grinder to about 59 degrees from the wheel face. Hold the bit between your thumb and index finger with the cutting lip horizontal. Touch the lip to the wheel and simultaneously rotate the bit clockwise (viewed from the shank end) while lowering the shank slightly. This creates the relief angle behind the lip.
The motion takes practice. You're rolling the bit about 180 degrees while dropping the shank a few degrees. Do one lip, rotate the bit 180 degrees, and do the other. Then check: both lips should be the same length and the same angle. If one lip is longer, it does all the cutting, the hole comes out oversized, and the bit vibrates. Hold the bit point-up against a dark background to check lip symmetry. Grind the longer lip until they match.
Using a Sharpening Jig
A drill bit sharpening jig clamps the bit at the correct angle and guides it against the grinding wheel. The Drill Doctor (DD350X or DD750X) is the most common consumer sharpener. You insert the bit, the chuck aligns it to the correct point angle, and a cam mechanism rotates the bit against a diamond wheel. Results are consistent but the machine costs $70 to $130.
Simpler jigs that mount on a bench grinder cost $20 to $40. They hold the bit at 59 degrees and let you roll it against the wheel by hand. The angle is fixed, so the results are more consistent than pure freehand. For someone who sharpens bits a few times a year, a $25 jig and an existing bench grinder are the practical setup.
When to Sharpen vs. When to Replace
Sharpen when: the bit is dull but the flutes are intact and the bit isn't bent. Standard HSS bits can be sharpened 5 to 10 times before they're too short to be useful. Cobalt bits resharpen well too.
Replace when: the bit is bent, the flutes are damaged, or it's a specialty bit (brad point, Forstner, step drill) that requires factory geometry. Carbide-tipped masonry bits can technically be resharpened with a diamond wheel, but the cost and effort usually exceed the $3 to $5 replacement cost.
For twist bits under 1/4-inch diameter, resharpening by hand is difficult because the geometry is small. Most people replace these and save sharpening for 1/4-inch and larger.
Frequently Asked Questions
What grit grinding wheel should I use?
A medium-grit aluminum oxide wheel (60 to 80 grit) works for HSS and cobalt bits. Don't use a coarse (36 grit) wheel; it removes too much material and overheats the cutting edge. For carbide bits, you need a diamond or green silicon carbide wheel. Aluminum oxide won't cut carbide.
Can I sharpen drill bits with a file?
Technically yes, with a fine diamond file, but it's slow and hard to maintain consistent angles. A bench grinder does the job in 30 seconds. A file takes 5 minutes and the results are less consistent. If you don't have a grinder, a file works in a pinch for bits above 1/4-inch.
How do I know when a bit is dull?
The bit produces dust or fine powder instead of curled chips. It needs more pressure to penetrate. The hole edges are rough or discolored from heat. The bit squeals or chatters. Any of these means it's time to sharpen. A sharp bit makes a clean hole with spiral chips coming up the flutes.
Does the point angle matter?
Yes. 118 degrees is the general-purpose standard. 135 degrees is better for harder metals (stainless, hardened steel) because the shallower angle reduces the cutting force needed. Steeper angles (90 degrees) are used for soft materials like wood and plastic. For most workshop sharpening, 118 degrees covers everything.