Most twist drill bits, including bits designed for high-speed drilling, have a pair of cutting faces at the tip of the bit, followed by some spiral-shaped grooves for guiding away material that is cut from the hole. With regular use, the cutting faces (also known as lands) can dull or become chipped. You can sharpen a high-speed drill bit or other twist bit on a bench grinder with a simple jig made from an angle iron.
Turn off the bench grinder and lift the shield up and out of the way.
Align the angle iron flat on the tool rest, perpendicular to the face of the main cutting wheel on the grinder. The end of the angle iron should be parallel to the cutting face, positioned about 1/2 inch away from the grinding wheel. Clamp the angle iron to the tool rest with a small C-clamp.
Place the drill bit you want to sharpen into the inside angle of the angle iron, with one land directly over the other. Ease the bit forward, so that the bottom land is barely touching the motionless grinding wheel. Loosen the set screw on the adjustable tool rest and adjust the angle of the rest so that the bottom land is flat against the grinding wheel. Tighten the set screw to lock the tool rest in position.
Slide the bit away from the grinding wheel and turn on the grinder. Verify that the bottom land is directly beneath the top land, and ease the bit forward, grinding the bottom land on the wheel. Grind for two to three seconds, then remove the bit and inspect the grinding. The grinding should be clean across the face of the land, with no visible gaps. If necessary, place the bit back into the jig and regrind this land.
Flip the bit over and grind the opposite land in the same manner as the first.
Remove the bit from the jig and inspect the tip of the bit. Both lands should be cleanly honed and of equal length. If one land is shorter than the other, regrind the shorter land until both are of equal length.
Grind in short, two- to three-second bursts to avoid overheating the bit and causing the steel to lose its temper. Overheating a bit will allow it to dull more quickly.
When grinding, wear appropriate clothing and safety glasses to protect against flying sparks.
Tips and warnings
- Grind in short, two- to three-second bursts to avoid overheating the bit and causing the steel to lose its temper. Overheating a bit will allow it to dull more quickly.
- When grinding, wear appropriate clothing and safety glasses to protect against flying sparks.