Thu May 16, 2013 4:05 am
It's good to go back to basics to understand appropriate use of microbevels. And yes you will see me echoing concepts that BDL is hinting at.
An edge on a piece of steel is set at some angle. Given the quality of the steel, if the angle is made more acute it will cut better but loose robustness, more easily failing for a given task. Made less acute it becomes more robust but sacrificing performance. If the steel is softer it will not hold a more acute angle. So if you are using say a yellow steel usuba (low quality carbon steel), the angle of the single bevel will fail easily, giving you an edge that chips too easily. Make it less acute and it will hold up better but when it becomes sufficiently less acute, it will fail to perform the tasks assigned to an usuba adequately. Solution - don't buy a cheap steel usuba or you will suffer.
This holds true to a slightly lesser extent on a yanagi. No microbevels front or back and you get a very sharp edge [I'm referencing edge geometry rather than finish, not to derail the discussion]. Use an edge like this on a yanagi for chopping tasks and you will chip it out. Solution - don't do that! It is a slicer. If you find that your edge chips out easily, go for a less acute angle. How? Well you could use a microbevel on the front, back or both sides - not my choice, adjusting the included angle until it is performing adequately, or more subtly, you can make the front bevel slightly convex rather than flat, making the angle less acute. This is classically referred to as a hamaguri grind.
IMO, I find the idea of putting a 45 degree microbevel on a yanagi overkill. Extreme overkill. Bear in mind that it is far harder to remove a microbevel than to put it on. Putting on a 45 degree microbevel is quickly accomplished, but removing it requires bringing down the whole front bevel to the bottom of the microbevel - a lot of work.
Solution - IF you require a more robust edge, gradually increase the edge angle to what you require - nothing more. "choose the appropriate angles based on the particular knife and its use than according to a philosophy. " If you are using a yanagi that requires a 45 degree microbevel, I'd suggest a better yanaga AND better cutting technique.
A deba presents a more interesting case as does a traditional single bevel kiritsuke, since different parts of the edge can be used for different tasks. Here you can use a microbevel to advantage, using no microbevel near the tip where lighter duty tasks are performed and progressively increasing the angle of the microbevel towards the heel. This gives you delicacy for filleting a fish and robustness for chopping the head off with the heel portion of the blade. You could also do a hamaguri grind with the radius of curvature decreasing (more obtuse angle) as you approach the heel rather than using a microbevel.
There is no single school of thought on this topic - either here or in Japan. If you find yourself simply following 'tradition' or what some 'master' has told you, it is certainly worth doing a sanity check against the basic science of it all. Ideally you will fine tune your knife to your usage rather than just following general theory.