I resharpen drill bits all the time, even the smallest quickly with
just the flexshaft and an emery disc. First look at the angles on
the face of a new drill bit, to see what they look like when brand
new. This look is your goal when resharpening a worn bit.
I turn the emery disc so it faces away from the handpiece, and then
under a loupe I cut the angle of the cutting edge, taking care to
not overheat the metal. Light, and quick is all it takes. Make sure
the angle of this cutting edge is the same on both faces. Next I cut
the relief faces, to leave the cutting edges.
Keep practicing, and comparing the results with a new drill bit, til
you are satisfied with the results. If you have done it well, the
resharpened bit will cut just like new, and I can resharpen even
shattered bits, if I go slowly, and do not try to grind too much at
once. It takes practice to keep from burning the delicate drill bit.
If that happens, the bitis history.
As soon as you start to drill again, you will know if you got the
bit sharp. If not, it only takes a few seconds to recut it. The
entire process takes far less time to do, than to describe here.