I use an 80-grit flapdisc on my 5" grinder......makes a razor sharp edge (on axes, scrapers, shovels, hoes, edgers, lawnmower blades, etc.) literally in minutes. The key is to NOT get the edge hot. Take your time, don't press the disc onto the metal (let it eat at it's own pace), working the disc back and forth. Grind the edge TOWARD the axe, not away from it.....
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These are super useful tools .My other favorite is a cup brush (not good for sharping but cleans up rust fast)
everyone needs a Matabo!
If my Matabo is to far away I've used a orbital palm sander & a vice also]