If I were you I would get a 4' angle grinder with a sander attachment. Figure a way to clamp that corn knife to the workbench top. Now get to work on that edge. omething like 600 grit paper will be for a pretty fine edge. I would see about some 400 grit. You need to concentrate on hitting that edge with a consistant angle every time you hit it ( and that my friend is where you are not doing your end of the work, I'm fairly lousy free hand too ) . Go easy as you can over heat the steel and remove the temper.
As far as the differences in edge think of the shape of an axe bevel. You cannot lay a straight edge from the edge to the beef of the axe. It is a compound curve. I have seen people use sand paper on a mouse pad and drag the edge "backwards " to get the desired results. The idea is to have a lot of material making up the edge for increased strength. At the same time you have removed some material from the blade so it can move through the work easily. Imagine starting with a 17 degree bevel, giving you that edge you want. Now go over the whole thing with a 25 degree angle, and finally going over it at a 30 degree angle. The leading edge is not quite as sharp but it has more strength, not only that but the steel behind that edge is a bit thinner than it would be were it all at 30 degrees, and is "out of the way" allowing the knife to slice with less effort. It may not be as technicly sharp, but it cuts and feels easier to use. Way back in the day everything was sharpened by hand and was an art this sort of bevel was common. Concave edges cannot really be duplicated with a machine as a straight bevel can be done. Now days a concave beveled knife is pretty rare as hand work is very expensive.
Check out Falkniven knives it seems they have a pretty good piece on the details, and pictures do wonders.
