It really is a hard thing to answer simply with black and white terms, that is, do it this way, and don’t do it that way. There’s a lot of factors we’re dealing with and the uneven bevels are really about steering, or actually correcting for it. That is the way the knife moves off to the side, as it cuts and passes through what your cutting or slicing, because of how its ground. I’m attaching a post written by Jon Broida, that I copied with his permission. Jon is a Japanese Knife Importer and expert knife sharpener. I hope this gives you some background on what the knife maker’s are intending to accomplish by applying an uneven beveled edge.
(Excuse the copy and paste, but I know I’ve put this up on this forum before, somewhere)… As for asymmetry, it seems that this is a rather confusing issue for many. Part of the confusion stems from the fact that many of the ways that we describe these asymmetries are gross oversimplifications. For example the ratios like 50/50 or 60/40 don’t really describe anything of substance. Is it the ratio of the percentage of sharpening on each side? Is it a ratio of the angles on each side? In reality it’s neither. No craftsman in Japan measures the angles or determine ratios. What really matters is the way that the knife cuts. The asymmetry deals with two main issues – the thinness behind the edge and steering, that is, how the knife deflects when cutting. The more asymmetrical a knife is, assuming the angles are equal, the thinner the knife is behind the edge. However, the more asymmetrical the knife is, the more likely it is to steer. It’s also important to keep in mind that the angles are not always equal. When figuring out asymmetry for any given knife, the first thing that you want to do is cut with the knife. When you cut with a knife, you want to assess whether it is steering to the right or to the left, and how easily it moves through the food. If you notice that your knife is steering to one direction or the other, you want to create more surface area on the side that it is steering towards, so that the knife cuts straight. This can be done by adjusting the angle (either more or less acute) and/or adjusting the amount of time spent sharpening on each side. If you notice that the knife is wedging in food as it goes through it, this may mean that you need to sharpen to a more acute angle, or that you need to thin behind the edge. Some of this can also be dealt with through adjusting asymmetry, as previously mentioned.
In general, there is not going to be an exact angle that is correct, but rather a range of angles that works. For instance, most double bevel Japanese knives will work well with angles somewhere between 10-15 degrees per side. The closer you are to the 10 degree side of things, the sharper the knife will feel, but it will also be more fragile, brittle, and may not hold its edge as long. The closer you are to the 15 degree side of things, the more tough and durable the knife edge will be, though it wont feel quite as sharp. It’s also ok to go even lower or higher than this, depending on your personal preference, though I often recommend staying within this range until you have a better understanding of how things work for you. For what its worth, Japanese craftsmen aren’t measuring the angles when they make or sharpen the knives either. Lastly, it’s important to keep in mind that you don’t have to always use the exact same angle. If you want your knife to feel a bit sharper, go a bit lower. If you need a more tough and durable edge, go a bit higher. So, like I said before, take this info and then decide if you want to spend more time sharpening on one side or the other, and at what angle you want to sharpen in order to get the knife to cut the way you want it to. I hope this make sense and helps….
“tcmeyer” wrote in his response above in this thread that the uneven bevel is intended to allow the knife to be used to make narrow, straight, thin slices from the exposed end of the food you’re cutting, while cutting straight down through the food without the knife blade slipping off the end of the food.
For my personal 70/30 asymmetrical beveled right handed Japanese chef’s knives. When I sharpen these with my W.E., I apply a 14° bevel to the left side and a 20° bevel to the right side. This is while holding the knife by the handle, in my right hand, with the sharpened edge down and the spine up. This 70/30 angle combination has given me good cutting results. It’s easier to sharpen angles then try to figure a ratio of applied sharpening effort of 70% to one knife side vs 30% to the other side. This way the apex is centered and the taller bevel, of the narrower angled bevel, is facing the food I’m cutting. It seems to allow me to cut thin even slices straight down through the end of the food, like I need it to.
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