I bought a Drill Doctor many years ago. It makes excellent, even cutting edges, but I struggle with it putting the proper relief on bits. I have a little container full of dull bits that I had good intentions of sharpening one day, but that one day has never shown up yet. Watch the video posted, it’s good. Also consider buying one of these gauges, they will help get the right angle and get the cutting edges even when you’re grinding by hand. It’s very important to have the cutting edges even, or one will do all the cutting and you can get an oversized hole.

https://www.amazon.com/General-Tools-16ME-Multi-Rule/dp/B00004T7T7