I'm with Matthew on the essential impossibility of honing flat, freehand (on a cutter not hollow ground).
I'm with Jacob in that there is a difference in 'rounding under' and everything else. I'm positive that Japanese craftsman would err on the side of rounding under, be it ever so slight, the effect at the cutting edge is entirely and exactly the same as Jacob's method. I am practically positive that the Japanese do not hone a hump into the cutter right behind the edge, nor does Jacob's method. Again, if anything, they remove an extra bit of steel right behind the edge which can only be achieved by a slight lowering of the cutter during its movement on the stone. It starts at the desired angle (which of course is the 'flat' grind in the first place) and never moves higher. There is not an attempt, conscious or otherwise, to raise the angle above that of the flat grind. Otherwise, then, they would simply be introducing a higher microbevel which they do not do. Accordingly, there are really only two options - hold it PERFECTLY at the starting angle or DIP IT - little or a lot, doesn't matter one whit at the cutting edge though the attempt is to hold it on the 'grind' angle.
This all could easily be tested by holding a straight edge against a traditional Japanese plane iron, honed by an experienced Japanese craftsman, and viewing under relatively small magnification. The angle will be seen as highest at the edge and going lower behind it. You might find 1 out of every Xth cutter that might be considered 'perfectly' flat at that particular low magnification. The 'error' (it's really not an error just not perfectly flat which they consider the ideal) on the rest would go the other way - lower behind the edge.
I'm with Jacob in that there is a difference in 'rounding under' and everything else. I'm positive that Japanese craftsman would err on the side of rounding under, be it ever so slight, the effect at the cutting edge is entirely and exactly the same as Jacob's method. I am practically positive that the Japanese do not hone a hump into the cutter right behind the edge, nor does Jacob's method. Again, if anything, they remove an extra bit of steel right behind the edge which can only be achieved by a slight lowering of the cutter during its movement on the stone. It starts at the desired angle (which of course is the 'flat' grind in the first place) and never moves higher. There is not an attempt, conscious or otherwise, to raise the angle above that of the flat grind. Otherwise, then, they would simply be introducing a higher microbevel which they do not do. Accordingly, there are really only two options - hold it PERFECTLY at the starting angle or DIP IT - little or a lot, doesn't matter one whit at the cutting edge though the attempt is to hold it on the 'grind' angle.
This all could easily be tested by holding a straight edge against a traditional Japanese plane iron, honed by an experienced Japanese craftsman, and viewing under relatively small magnification. The angle will be seen as highest at the edge and going lower behind it. You might find 1 out of every Xth cutter that might be considered 'perfectly' flat at that particular low magnification. The 'error' (it's really not an error just not perfectly flat which they consider the ideal) on the rest would go the other way - lower behind the edge.
