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What type of axe?
For most, get rid of any nicks, chips or flat parts in the blade with a metal file keeping the profile the same (so removing minimal metal but consistently around the whole edge).
Then get sharp with a stone (best ones are round, allows you to grind circles around the edge) or medium then fine sand paper on a wood block.
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Smallish hatchet.
best ones are round, allows you to grind circles
Something like https://www.heinnie.com/lansky-puck ?
I've got an axe to grind. How do you sharpen yours?