+1 to Kippington's thread and Jons reply.
There are a couple things I don't quite understand about asymmetric (say, single bevel, in the extreme) edges. If anyone has some input about how much of the following is on track, I'd love to hear it.
*****Why make/use them?*****
As far as I can see, there could be 4 reasons. For single bevel knives, they would be:
a) In some (for me, unusual) applications, like making sheets of cucumber using a rotating cut, the steering that comes with a single bevel can be useful.
b) In a (right handed) single bevel knife, the edge bevel and globally convex geometry on the right side should push food away as you're cutting it, so it doesn't stick to the knife. You don't usually need the knife to push away the food on the left side, because you're holding it with your other hand, so it makes sense to concentrate this effect on the right by putting the bevel there.
c) It's (a little more than) half as much work to sharpen a single bevel knife.
d) People often say that single bevel knives are sharper, because of a smaller total edge angle. I'm a little confused about this, though, since then the question is "why don't we just sharpen double bevel edges with half the angle?". I'm guessing that there's something about the shape of the single bevel that makes a single bevel edge with 15/0 angles more durable than a double bevel with 7.5/7.5 angles? (I don't get why this would be true.) Additionally, I could imagine that it is easier to sharpen 15/0 than 7.5/7.5, because maybe it's harder to hold the small angle.... I'm just guessing blindly here though.
For double bevel asymmetric knives, c) isnt relevant, and lets forget about a) since I dont work in a Japanese restaurant. So, it seems like the main points would be b) and (maybe?) the ability to get smaller total angles because of some mysterious sort of increased durability in an asymmetric edge?
*****How to sharpen asymmetric double bevel knives*****
Let's assume we don't want our knives to steer. I get that the point is to correct the steering effected by the overall geometry of the blade by sharpening the edge asymmetrically. (Although as Kippington explains, when you have a clad knife it's also important to line up the edge with the center of the blade so that the edge is just composed of the core steel.)
Presumably, the exact amount and direction that the knife steers is some complicated quantity depending on the overall geometry of the knife, the angles and lengths of the edge bevels, and maybe the position of the edge relative to the rest of the knife.
You can understand how the edge position and the lengths of the edge bevels change under sharpening as follows. Essentially, these changes depend on the angles chosen for each side, and the time spent on each side.
For instance, here we have a (rather dull) 45/45 angle double bevel. After sharpening 3x as much on the right side, the edge moves to the left, and the right bevel gets longer than the left bevel.
Here we have 23/14 angle double bevel, and we sharpen the same amount on both sides. The edge moves slightly to the left, since the perpendicular to the 14 side points more to the left than the perpendicular to the 23 side points to the right, and the right bevel gets relatively longer.
(Ok, in my picture the bevel on the right side also starts out slightly longer, so maybe itll actually take a bit longer to take metal off of that bevel, since the finger pressure is distributed over a larger area. Not sure how much this will matter, though, i.e. if it would cancel out the effects mentioned above.)
Presumably, if the overall geometry of the knife makes it want to steer to the left (as I guess is the case for right handed asymmetric knives), making the left edge bevel longer and a higher angle will compensate for that. As long as you can keep the edge basically in the center (should we make sure to do this for monosteel knives, or are there reasons not to?), you can basically balance the asymmetric angle ratio with the asymmetry in time spent on the two sides however you want, it doesnt matter too much which method of compensating for steering you emphasize more. Although I guess I can imagine that if you just decide Im just going to make the angles equal on both sides, and spend more time on the left side you could maybe get all the way to a (left-handed) single bevel edge without completely compensating for the steering.
Anyway, sorry for the neverending post. I realize that my goal to
*completely figure out how the amount of steering is affected by the blade geometry, and to maximize how much my knife pushes away food to the right, while simultaneously compensating for steering and putting the edge right in the center*
will be completely impossible to implement using freehand sharpening (or any other kind, really), even if I somehow completely understand the geometry and composition of the knife Im using. So, of course, Ill mostly just try to compensate for steering by feel. It will definitely make me feel more comfortable with the whole thing if I have a good picture in my mind of what I am doing, and what I should be shooting for, rather than turning everything into trial and error.