Single Bevel Deba Challenge
- This topic has 4 replies, 2 voices, and was last updated 05/29/2020 at 3:57 pm by
.
-
I am trying to replicate the factory single bevel on my WEPS for fun, interest and future fine tuning. It is an Aritsugu 7 inch Deba (blue steel) my son & wife brought me from Japan. It is extremely thick and heavy. The spine is ~0.25 inch thick with a one sided primary bevel ~0.5 inch in width. It is slightly dished on the opposite side. I bought the accessory WEPS jaws to hold it. It also has a micro bevel (thru USB micro inspection) which is more obtuse at the heel vs. the tip (for chopping fish bones vs. fine slicing at the tip). I mounted the blade in the hope of being able to polish up the primary bevel as well as the micro bevel. I love the alignment guide which makes future setup a piece of cake. Here is my issue:
After mounting the knife I was unable to find a position which would allow me to closely follow the original primary bevel. I know this is because it was done by hand by the original craftsmen but I figured I would give it a shot. I am familiar with Anthony Yan’s geometric analysis and how you can vary the angles based on knife position in the WEPS although I do not remember the max possible variation. I clamped the knife (see pic) to the table and using the angle indicator I determined that the primary bevel changes by ~5 deg over the 7 inch length of the edge. I know that I can keep the knife as is (it is super sharp) but someday I will need to sharpen it.
Does anyone have any suggestions of the max variation possible or other ideas ?
My Aritsugu came with a much more slender blade and a 12 degree inclusive final edge bevel. I haven’t sharpened it yet, but I have sharpened my sister’s twin to it. With my Low Angle Adapter and extra-long 12″ rods, I was able to get down to 16 degrees inclusive (8 dps) on my Gen 3 Pro (2017).
The masters at the Aritsugu shop in Kyoto sharpen in two stages – first on a rotary drum abrasive,with the blade held at the top and parallel to the drum’s rotational tangent, then with a more typical sharpening on waterstones, but with a very low angle. You can see them work in one of several Youtube videos.
I’ve been starting with 800 grit diamond stones, then progressing to 1500 grit. I then continue with 6, 3, 1.5 and 1.0 micron diamond films on brass platens (aluminum or glass will do as well), using 50 to 100 strokes per grit. At the finish, I have an edge refined well beyond that supplied by the Japanese masters.
I don’t think there is any value in trying to replicate a variable bevel angle, as I cannot imagine why one would attempt to create one deliberately.
Judging from your photos, I think you can calculate the factory angle with a little trig by measuring the width of the bevels and the thickness at the bevel shoulders. You’ll want to use an angle somewhat more acute, as trying to replicate the factory bevel angle would require a very extensive stoning process.
Using your method (finding the angles relative to the side flats) requires that you use the internal included angles, including the one at the shoulder of the bevel. A bevel angle of 15 degrees would have an included shoulder angle of 75 degrees, assuming that the side faces are dead-flat and parallel to one another. Ninety plus fifteen plus 75 is equal to 180 degrees.
We never care about the shoulder angle, relative to the primary (side face) grind, because it isn’t important. What is important there is the thickness of the blade at the shoulder. With your blade, which we would call a chisel grind, the included angle is going to be much lower than average and as such, capable of a extremely sharp edge. A bevel angle of 15 degrees will be the equivalent of a double-bevel blade sharpened to 7.5 dps. Whoo hoo!
I’ve brought up the issue of chisel grinds and offset bevel edges on several occasions, and now I’ll do it again. The bevel edge side (or the wider bevel) should be put on the outside face of the blade as you hold it in your hand and look down on the spine of the blade. If you’re left-handed, the bevel should be on the left side of the blade and if you’re right-handed, the bevel should be on the right side of the blade. Like a wood chisel, the flat side will fix the direction of the cut. The bevel side will tend to push the edge toward the flat side and the flat side will refuse to move. If you turn it around, there will be little resistance offered by the thin slice being cut off
I have a Chicago Cutlery cleaver that I sharpened with a chisel grind. As I recall, the bevel is at about 20 degrees. The bevel is quite wide, so the thickness at the shoulder is probably about 3 mm. If I try to cut summer sausage with it in my left hand (I’m left handed) I can cut slices about 1 mm thick. The slices happily fall away from the blade. But if I switch to the other hand, I am unable to cut a straight slice less than about 25 mm thick. As I progress through the cut, there is less and less strength in the slice being cut to resist the forces produced by the face of the bevel being pushed away from the body of the sausage. Trying to cut thin slices from a radish is a real trick.
4 users thanked author for this post.
- You must be logged in to reply to this topic.