The usuba is not a general purpose knife. If you have an usuba, and you don't want to use it as an usuba, why did you buy an usuba when there exist far better alternatives? Don't try to make an usuba into a all purpose knife because it isn't one. Sharpen it properly, and use it for what it is good at. That does not exclude using it for other things, but you should not be designing the edge around using it for other things.
I went back to further qualify my suggestion about light elevated honing on the "flat side"--I realized that it was not clear how little that I intended this to be done. It is really intended to deburr the edge and remove any tendency of the edge to curve towards the flat side. The intent is an edge that is beveled on one side with maybe a few microns of bevel on the "flat side".
This happens when you work the the back flat on the stone, just enough to deburr. There is no point to raising a microbevel. The fact that you have use the form of the knife to hold the angle ensures that the angle is consistent as well.
The intent is to avoid an edge that instantly folds over towards the flat side when any pressure is applied. There is no structural support on the flat side once the edge tips over the plane of its grind.
This is BS, if you did the same thing with a normally sharpened knife, you wouldn't have instantaneous failure. If you do experience instantaneous failure, then it is your failure in sharpening the knife and leaving a weak burr that folds over. This is a test anyone can do, even with a double bevel knife.
Lets not forget some basic tools like the plane don't have support directly behind the edge in the direction they are cutting. Anyone who whittles with their knives can also attest to this fact because they edges do not instantly fail. We're comparing merely hitting hitting some wood with an edge compared to actually cutting into wood. Its not the fact that there's no support behind the edge, it simply has to do with the toughness/hardness/durability of the knife.
As the knife moves down, a load is placed on the edge in the opposite direction. However, it can clearly be seen that there is no support directly behind that edge shown as the empty gap marked with blue crosshatch.
The edge is stronger if you remove the burr and bias it slightly (much less than a millimeter) towards the beveled size.
Honestly, I don't know how one can bias a burr. Either you mean you produce a bevel less than 1mm in size or you mean you only change the angle by whatever it is equivalent to in 1mm of movement.
The flat polished area on the back should be less than 1mm anyways. 1mm is not a small amount when talking about these knives. The only place it is really permissible to put a bevel on the back is on the heel of a deba. That is because that part is used less to fillet, but it is used to shop through the spines of the fish.
Protection against column buckling only occurs up to the angle you increased it by, so if you're only changing the angle by 1mm, it only gives you 1mm more play before such alleged column buckling occurs.
This will not impact cutting performance, but will enhance strength.
Its true that it will increase strength, but it does affect cutting performance. Cutting happens on an extremely small scale, and if the microbevel is large enough to significantly alter the edge strength, that is significantly larger than the edge radius, then it is likely that it changes the angle that the edge cuts at and the displacement it causes on a small scale, changing the finish of the cut. Now some people may argue that the finish of the cut doesn't matter, but then why an usuba?
The concave surface on the flat side is much like the concave surface on a straight razor. It provides relief behind the edge to reduce drag and provides a natural honing and stropping surface,
That is if you use it as a honing and stropping guide and don't add a microbevel.
as razor makers have noted for over 100 years when you hone (with a stone) at nearly zero degrees you develop a tenacious burr that needs to be cut off.
This is BS. Most razor honing doctrine now days is based on the idea of working both sides to avoid creating a burr. 0 degrees relative to what? Theres also no such thing as 0 degrees, and therefore sharpening at 0 degrees can not have any bearing on the edge. The only issues would be sharpening too accut, which is not 0 degrees, or too thin or such.
Heres some diagrams of some hypothetical blade designs and closeups. 1) A fat spined straight with a rather large included angle, 2) A slimmer straight, 3) A single beveled blade, possibly a razor, 4) A frameback, or possibly a normal knife in a clip-on jig, and 5) A knife held at a similar angle during sharpening. With the exception of the first, all of them are meant to have approximately the same angle, and the similar thickness right behind the edge. Get close enough, and the arc of the concavity loses significance, and so does asymmetry, or whether or not it is even hollow ground. This is the scale that burrs develop on. Why would a burr care about the macro difference in the form of the blade? The only one that is different is the one that is at a different andle, and that would still be sharpened at "0 degrees" simply 0 degrees relative to its faces.
When you create a knife edge that resembles an asymmetric straight razor blade you need to take care of some of the same needs plus the additional weakness caused by an edge only supported on one side.
Outside of microtomes, asymmetrical straights just happen to be Japanese. The issue with razors is trying not to raise a bur in the first place. That has nothing to do with sharpening at "0 degrees." It has everything to do with not overworking one side too much.
Now you can try for the perfect edge, but that's not the direction I would give a novice working his way up from using a notch sharpener. I think he will get the most usefulness out of his knife if he sharpens it himself and uses it often. A sharpening job that gets him 95% performance is better than pushing him to expensive professional service. If his knife is reserved reverently rather than used because it is too expensive and too much trouble to maintain it "properly" the knife will be wasted. In addition there is much to be learned from using kitchen knives and sharpening them that is missed if he goes down that road.
When did I say he should use pro services? Why can't he get "100%" himself, or at least not get 95% of what he could get himself? In fact, when did anyone say he should use pro services? What was said was that most of the pros who do specialize in Japanese kitchen knives are usually a helpful bunch, and you should be able to find at least one that would help you for free, or supply you with equipment to sharpen yourself.
Sharpening a Japanese chisel ground knife is arguably easier to do than a double beveled one, as long as you know how to, and you are interfering with that. The front bevel should be worked to expose new steel, either flat to the bevel like a scandi, or at an angle like conventional knife. Then the back is worked just enough to produced a ring of polished flat at the edge and enough to deburr the knife.
An usuba is wasted if trying to sharpen it to be a general purpose knife because it isn't a general purpose knife, and it will never do general purpose particularly well. An usuba should be used to do things it excels at.
Tell you what, after you have been sharpening things for 50 years like I have maybe you will start to grasp what I am saying. For now I don't have time to try and push through your closed mind.
You might know something about sharpening, and you might have 50 years under your belt, but it doesn't mean you aren't wrong. It just means you're stubborn and close minded because you think you're right thanks to having 50 years under your belt. And when it comes to usubas and chisel ground knives, I'm rather inclined to think that you aren't.
