Japanese single bevel dimensions question

Sando

Sando

Knife Maker
Joined
Jul 4, 2002
Messages
1,148
I'm working on a set of Japanese Kitchen knives and I'd like to get the geometry as close as possible to 'correct'. There's 3 dimensions I'm wondering about in this diagram. (The drawing is not to scale; it's exaggerated to show the issue.)

The angle A I 'think' should be about 12 degrees. The radius R for the urasuki (concave section on the back of the blade) is a total puzzle. Perhaps it is from a 30" wheel? The distance of the urasuki to the edge is about 1/4? Maybe?

Single%20Bevel.png


I know dimensions are going to vary from maker to maker. I'm just wondering about the ballpark numbers for these bevel grinds!?
 
While your drawing may be exaggerated, it is very misleading. I hope that is nothing like your plan.

The urasuki starts about 1/8" to 1/4" from the edge (depending on overall blade size) and goes about 2/3 to 3/4 up the back side. The radius is whatever makes that grind on your blade - normally, between 24" to 36" radius.

The primary bevel on the front goes up around 1/2 way. The angle is not important, as it is whatever the geometry of the bevel height and the blade stock thickness creates. This is usually around 10 degrees.
 
Thanks Stacy!

Yes the drawing is very misleading and not what the knives are looking like. It was only to ask the question.

The Usuba is about 2" wide on .120 thick stock. Hmmm the bevel half way up would be ~7 degrees!? I should have started with larger stock. At 10 degrees that would be about 5/8" high at this thickness. Oh well. This one is for my use. I'll make another at 0.180" thick and 10 degrees will get half way up.

For the urasuki I have a platen with a 12" radius (mimics a 24" wheel). I'll make another for a 24" radius (4' wheel).
 
Stacy E. Apelt - Bladesmith Stacy E. Apelt - Bladesmith

Just so you know I understand. I made a scaled drawing with your parameters. This one is 2" high, 0.180" thick, and a 15" radius (a 24" radius and you can't see it in the drawing :) ) The uraoshi is 1/4" and about 3/4 the way up the blade and the bevel is 10 degrees and half way up.
Bevel.png
 
I make usuba at 7 to 9 degrees. If the edge is too frail, put a micro-bevel on it at 15 degrees.

You have to ask yourself when drawing/designing a knife with a wide blade what the 99% above the edge is for. If it won't be for scooping up chopped food to transfer to a pan/pot, then a less tall blade is probably a better blade. I do usuba from 1.25 to 1.75". While the idea of scooping up chopped veggies sounds cool, to be honest, I rarely use the knife blade for transferring the cut food. If that is a task you will do often, make a dedicated food scooping spatula or board knife ... I use a pastry knife as my scraper/pick up tool.
 
The belt does it for you. Use a not new, but still good 400 grit belt - have the belt tension tight and run the grinder at a crawl. Place the zero edge bevel on the belt top just behind the top roller of your flat platen. Lift to around 10-15. Draw the edge across the belt a couple times. Upon examining with magnification, you will see that the last tiny bit of the bevel convexes into the edge … as shown in the enlarged diagram by milkbaby.

I convex the edges of most of my kitchen blades. I have a chef who only has me sharpen his blades. He says he has done his own, and had sharpening services do them, but mine cut better and stay sharp longer. I old him the reason was the convex micro-bevel … and that I give each side of the edge a single pass on the buffer after sharpening. I also cut a large piece of cardstock up into slivers to clean up the edge. The first two cuts may seem like the edge is bad, but then, holy cow, the thing cuts like a laser.

Besides the need to be VERY CAREFUL when buffing the sharpened edge, you also have to be gentle. Heavily buffing a newly sharpened edge can give it a rounded edge and make the knife much duller. I buff just enough to polish the final convex, but not enough to entirely remove the wire. The cardstock removes the wire. I use matchless white for the charge on a well worn 6" unstitched pure cotton wheel.
 
I ground the bevel at 12 degrees for a first look. Yeah, I see what you mean, it can go further. I took it to 10 degrees and will stick there for this first attempt.

M milkbaby Thanks so much for that diagram. It's exactly what I needed to study. It's interesting he has the bevel at 14 degrees. But I like Stacy's thin as it can go mantra.
 
It all depends on whet the knife will cut. Fish cuts great at 10 degrees, chicken a bit higher angle, and veggies around 15 degrees.
 
You must log in or register to reply here.
Back
Top