I used to sharpen my chains....when I was clueless....now I just keep my chains razor sharp
. I hit them with a hand file just a few strokes freehand on just about every tank of gas....that's the key...never let 'em get un-sharp. But by hand, the teeth eventually get caddywhompus on one side (longer)....no bueno, or I hit a nail or something. Hard to correct by hand...
I picked up a mid-range Oregon chain grinder from Northern Tool a few months back....wish I'd done it decades ago
.