Bob Engnath on the problem of creating taper in a long blade with ridge line.
What I've been doing is grinding the portion from the shinogi to the cutting edge first, since that's the largest cut and removes the most bulk. Normally, the shinogi is one third of the way down, and the average fellow would stop the grind there. I don't, especially out towards the tip. My rough cut is at the one third mark back at the machi area, where I want a full 5/16 " thick, but tapers gradually up to the spine at the area a few inches behind the tip.
Then, when I grind in the upper cut, and bring the shinogi down to the one third mark, I'm reducing the thickness of the sword as I cut into the area where I've already cut with the original cut.
If you draw it once, in cross section you've got the technique. As long as I make my first grind nice and even as it runs up the blade, the sword will taper to about two thirds thickness at a point just behind the tip. I use this on European blades too, and it works great!
This is one of those darned simple things that makes you smack yourself on the forehead when the light finally goes on.
I was saving one little detail for later. I do stop the thickness reducing cut short of the tip, so I'm able to put a little flair there. Sword tips?. They're a genuine pain in the ass to get right. Also possibly the easiest part to screw up.
As long as the primary grind is even, or has a straight top line to the grind its good. If it's full of bumps, etc., the thickness will end up sort of strange.
As I said, if you make it fall at the one third point at the machi area, and taper it gradually upwards as you go to the tip, or a little short of that, making the second cut will reduce the thickness in a very precise way.
It doesn't make too much difference where the second cut starts, but I normally begin mine at the machi, where there is a flat to judge how far to taper the grind to thin the spine.
My interest is to bootstrap up the whole business of making a Japanese style blade.
