Helpful Tips for Sharpening Drill Bits
Twist Drill
Due to the compound relief on the back of the cutting edge of twist drills, it is best to re-sharpen them using a jig or special machine such as a "Drill Doctor". These are nearly impossible to re-sharpen by hand.
Single and double twist auger bits
Use an auger bit file or a stone or triangular saw file, never a grinder. Check the drill carefully before sharpening and when filing. Each cutting edge should do the exact same amount of work, so be sure to keep the original profile. First, sharpen the inner spurs. Never file outside as this will change the size of the drill. Then file the cutting edge to the bottom - that is, file through the throat of the drill.
Groove and tenon milling head
Use a smooth auger stone to sharpen and deburr the flute. File the teeth with a small saw and file the nose, taking care to maintain the critical angle. The flat edge is sharpened with a flute machined stone. Never sharpen the outer edges.
brad point drill
Use an auger bit file or stone, or a small triangular saw file to sharpen spurs and knives. Keep both pairs of knives and spurs at the same height so they do the same amount of work. Take off as little as possible and make sure to file only on the spurs or the inside of the lip.
Flat spade drill
Using a very smooth file or small stone, carefully sharpen the front cutting edge, maintaining the original angle and keeping the ground level. Sharpen both sides evenly and check for level. If necessary, sharpen the brad points, keeping the point centrality. Never touch the sides of the drill.
Forstner drill
Unlike most drills, the Forstner runs on its edge. This scratches the circumference of the hole, and the jacks pass the chips down the throat. Use an auger bit file or a stone sharpening tip lift to work through the throat of the cutter. Keep the original angle and keep the edges straight. Use small rounded edge talc on the inside of the rim, using continuous motion to maintain the curve. Never touch the outside of the rim.
Serrated drill
Using a smooth auger or stone sharpened jack, run through the throat of the knife. Keep the original angle and keep the edges straight. File the teeth with a triangular saw, keeping the same height around the perimeter. It is rarely necessary to file Brad points. Never file the jack on the top or around the drill bit.
Pipe plug cutter
Use a smooth file to sharpen the knife, working through the throat of the knife. Keeping the original angle and keeping the edges straight, remove as little metal as possible. The rim should require very little attention; just make sure it's clean. If necessary, stone the rim with a very fine stone (such as honed). Do not file.