A bench grinder works well. I hold the left side edge against the wheel and roll it up, then repeat on the other side. The cutting edge must be higher than the back.Having both cutting edges the same is a bonus.
There is also a special grinder with a jig just for drill bits.
I have used my 4" hand grinder with fair results. I clamp it in a vise with wood spacer blocks, turn it on and pray .