Leo-
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 it’s there and measures angles or ratios. What really matters is the way that the knife cuts. The asymmetry deals with two main issues-thinness behind the edge and steering. 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, this may mean that you need to sharpen at 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. Does that make sense?
-Jon
So I apologise for my posting previously I was mislead through various articles on the subject.
Jon was away in Japan so it took almost 8 weeks for an answer although I hasten to add he always replies but he gets stacks of mails and answers them all.
The only thing I am not certain of from his answer is what food is the best test to see if the knife is steering straight . I have asked him although I can imagine it will in part depend on what purpose the knife has to check the steering.
If I get anther suggestion from Jon as to what is best to test the steerage of a knife I will post it on this topic.
I do not imagine that any real negative effects have been found having used my previous notes on asymmetric angles I know my own asymmetrics have been steering fine it does mean that it is real trial & error if you are presented with an asymmetric whose bevels have been lost& it may be a starting point to use the angles I suggested
Response from Jonathon Broida Japanese Knife Imports
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