In the 1980’s Paul Harvey would advertise every day as part of his radio program during my lunch hour for drill doctor. What was that program called, The Rest of the Story ? It was a fun-listen whatever it was called, admittedly a little biased, but who isn’t. I never bought one of those drill doctors, even though his sales pitch was really smooth. I discovered I could do a pretty good job at sharpening drill bits using nothing but sandpaper and a flat surface believe it or not. I use a piece of thick plate-glass for the flat surface, lay the sand paper on it, and holding the drill bit in my hand start with something like 180 grit Al O2 sandpaper, working my way toward 320 grit. I mark the sharpening part of the bit with a black Sharpie pen, and watch to make sure the black is disappearing evenly, so I know I’ve got the sharpening angle correct. I sometimes touch it up with a knife sharpening stone, Arkansas stone think. I’d have never thought this would work, but I tried it, and it works pretty well actually. The downside is it is somewhat time consuming. But I only have to sharpen drill bits once or twice a years, so not a problem from my perspective. If you just have a few bits to sharpen, definitely should be considered for a diy’er. In a pinch this can be done with only sandpaper, no flat surface, but that method needs some practice.