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 the workpiece. Throwing it away and grabbing a new one works, but a $1 bit sharpened in 30 seconds on a bench grinder cuts like new again.
The skill is not difficult. The geometry is two facets meeting at a 118-degree point. Once you understand what you are creating, the actual 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, called lips, that meet at a chisel point in the center. Each lip is ground at a 59-degree angle from the bit's axis. Those two 59-degree angles combine to create the standard 118-degree included point angle (59 + 59). This geometry is the general-purpose standard and handles wood, mild steel, aluminum, and plastic.
Behind each lip, a relief angle of 8 to 12 degrees keeps the heel of the lip from rubbing against the bottom of the hole. Without relief, the bit skates on the surface instead of biting in. Too much relief weakens the cutting edge, causing it to chip. The correct relief angle is a subtle but critical part of a good sharpening job.
The chisel point at the center does not actually cut. It pushes material aside by brute force. That is why drill bits need downward pressure to start, and why they tend to wander on smooth surfaces. Split-point bits have a small notch ground into the chisel edge that creates a cutting action at the center. This is why split-point bits self-center and start faster than standard bits. Most new bits from the factory are split-point.
Resharpening by hand restores the main lips but typically does not restore the split-point geometry. Hand-sharpened bits may need a center punch mark to start cleanly on metal. On wood, the difference is less noticeable because the material is softer and the bit grabs more easily. For a deeper look at bit types, see our Forstner bit glossary entry and cordless drill buying guide.
Freehand Sharpening on a Bench Grinder
Set the tool rest on your bench grinder to approximately 59 degrees from the wheel face. A medium-grit aluminum oxide wheel (60 to 80 grit) is the right choice for HSS and cobalt bits. Do not use a coarse 36-grit wheel. It removes too much material per pass and overheats the cutting edge, which can draw the temper from HSS steel and soften it permanently.
Hold the bit between your thumb and index finger with one cutting lip horizontal. Touch the lip to the wheel and simultaneously rotate the bit clockwise (as viewed from the shank end) while lowering the shank slightly. This combined motion creates the relief angle behind the lip. The entire movement is a smooth roll of about 180 degrees with a small downward arc of the shank.
The motion takes practice. Start with a few sacrificial bits from the junk drawer and expect the first several attempts to look rough. Do one lip, rotate the bit 180 degrees, and grind the other lip. Then check your work: both lips should be the same length and the same angle. If one lip is longer than the other, it does all the cutting. The hole comes out oversized, the bit vibrates, and the cut quality suffers. Hold the bit point-up against a dark background to visually compare lip symmetry. Grind the longer lip until both match.
Keep a cup of water nearby. Dip the bit after every few seconds of grinding to keep the temperature down. If the tip turns blue, you have overheated it and drawn the temper. You can still use the bit, but the edge will dull faster than a properly ground one. On cobalt bits, which run hotter than HSS, overheating is less of a concern, but cooling between passes is still good practice.
Using a Sharpening Jig
A drill bit sharpening jig clamps the bit at the correct angle and guides it against the grinding wheel, removing the guesswork from the process. The Drill Doctor (models DD350X and DD750X) is the most common consumer-grade sharpener. You insert the bit into the chuck, the mechanism aligns it to the correct point angle, and a cam rotates the bit against a diamond wheel. Results are consistent even for beginners. The DD350X runs about $70 and handles bits from 3/32-inch to 1/2-inch. The DD750X runs about $130 and adds split-point capability, which restores that self-centering geometry that freehand sharpening misses.
Simpler jigs that mount directly on a bench grinder cost $20 to $40. These hold the bit at the correct 59-degree angle and let you roll it against the wheel by hand. The angle is fixed by the jig, so the results are more consistent than pure freehand work. For someone who sharpens bits a few times a year, a $25 jig and an existing bench grinder are the practical setup. General Tools and Woodstock International both make well-regarded versions.
For shops that go through bits quickly, a dedicated sharpener pays for itself within a few months. A set of five quality 1/4-inch cobalt bits costs $8 to $12. Resharpening each one five times before they get too short means 25 uses per set instead of five. The math favors sharpening once the volume justifies the upfront cost of the jig.
When to Sharpen vs. When to Replace
Sharpen when the bit is dull but the flutes are intact and the bit is not bent. Standard HSS bits can be sharpened 5 to 10 times before they become too short to be useful. Cobalt bits resharpen well and hold their edge longer between sharpenings. The cost per hole drops significantly with resharpening, especially for bits in the 1/4-inch and larger range where replacements cost $2 to $5 each.
Replace when the bit is bent, the flutes are damaged or chipped, or it is a specialty bit that requires factory geometry. Brad-point bits, Forstner bits, step drills, and installer bits all have geometries that a bench grinder cannot reproduce accurately. Carbide-tipped masonry bits can technically be resharpened with a diamond or green silicon carbide wheel, but the cost and effort usually exceed the $3 to $5 replacement cost for standard sizes.
For twist bits under 1/4-inch diameter, resharpening by hand is impractical. The geometry is too small to control accurately, and the bits are inexpensive. Most people replace these small sizes and save their sharpening effort for 1/4-inch and larger bits where the time invested produces meaningful savings.
One additional consideration: if a bit has been overheated repeatedly (showing blue discoloration at the tip), sharpening restores the geometry but not the heat treatment of the steel. That bit will dull faster than a properly treated one. It still works, but expect to resharpen it sooner.
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. Do not use a coarse 36-grit wheel; it removes too much material per pass and overheats the cutting edge. For carbide bits, you need a diamond or green silicon carbide wheel. Aluminum oxide will not cut carbide effectively.
Can I sharpen drill bits with a file?
Technically yes, with a fine diamond file, but it is slow and difficult to maintain consistent angles. A bench grinder does the job in 30 seconds. A file takes 5 minutes and the results are less uniform. If you do not have a grinder, a file works in a pinch for bits above 1/4-inch. For smaller bits, the geometry is too fine to control with a hand file.
How do I know when a bit is dull?
The bit produces dust or fine powder instead of curled chips. It needs noticeably more pressure to penetrate. The hole edges are rough or discolored from friction heat. The bit squeals, chatters, or walks across the surface. Any of these signs means it is time to sharpen. A sharp bit makes a clean hole with spiral chips coming up the flutes smoothly.
Does the point angle matter?
Yes. 118 degrees is the general-purpose standard that works for wood, mild steel, aluminum, and most plastics. 135 degrees is better for harder metals like stainless steel and hardened alloys because the shallower angle reduces the cutting force required. Steeper angles around 90 degrees are occasionally used for soft materials like wood and acrylic where fast penetration matters more than edge durability. For most workshop sharpening, 118 degrees covers the vast majority of tasks.