Always look at the edge and follow the original bevel.
A grinding wheel can remove larger amounts of material than filing like nicks, or you have to restore a particularly worn blade. Be aware that the grinding wheel may get the blade so hot that the temper, or hardness, of the steel could be compromised. So if the steel turns a straw color, that’s bad. When using a grinder, have some water nearby to dip the tool blade and dry it off for the next pass.
On axes and hatchets, not all have the same blade bevel. You must maintain the edge in the exact center of the ax. Do the whole edge to preserve the shape of the blade, not just where there are chips or nicks. And be careful to not burn the edge.
Filing produces very little heat, so you won’t need to worry about ruining the temper of the blade.
Don’t overheat the tool, and grind a little at a time. Let the metal cool off on its own, or douse in water before grinding more.
Use a 6-inch or 8-inch wheel. The grinding wheel should remove the chipped metal, but not overheat the tool that ruins the hardness. Try a 60-grit aluminum oxide wheel with a medium hardness rating.