[Frogtop]

I use a dremel tool on slow speed with an emery and keep it moving so that the metal doesn't heat up. I agree if the the edge is exceptionally dull that starting with a file is the best way to go. Sharpen at a sharp angle mabe 30 deg rather than 20 or less like a knife. These thing are mini axes rather than knives. As mentioned above a knife edge will quickly dull and chip with a hacking motion rather than an slicing motion.