I need to cut a (roughly) 3mm keyway in a piece of 10mm brass rod and I don't have access to a mill. I do have access to most hand tools, though. Can anyone recommend a way I can cut the keyway? I'm not too fussed about accuracy, as long as its within +/- 1.5mm of the nominal width I'm happy. Also, if it matters, it will be about 5mm deep.