A Basic Explanation of Asymmetry

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Before I get into my post, just wanna be clear that I'm referring more to edge strength than I am to steering although I would assume there may be a difference in the way our knives cut

Kippington said:
No problem!

I can see why this is confusing.
The terms 'shallow' (acute) and 'obtuse' are directly related to sharpening angles. The descriptors 'shallow' and 'higher' are used for angle because of how we hold the spine at a certain height from the stone while sharpening.
The terms 'short' and 'wide' (long) refer to the length of surface area the bevel covers as it moves up the blade face. Some people use time on the stones as an indicator for short or long bevels (e.g. "sharpen twice as many strokes on the left side") but this is actually a terrible way of describing surface area as it holds little regard for both the condition of the blade prior to sharpening and the angles being used (e.g. grinding a shallow angle over an obtuse one can take a lot of time, but doing the reverse takes seconds).
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I figured you were referring to shallower angles but I think what I was trying to confirm was whether the microbevel is put on the right hand side in your case is because of the shallower angle or because of the shorter bevel on the right hand side. I'm assuming from the pictures that you're grinding more on the left hand side at an obtuse angle (compared to the right hand side) and also developing taller bevels. I would assume that sharpening this way would lead to the apex favouring the right hand side in your case and the micro bevel on the right hand side would then be beneficial to centre it/straighten it more and strengthen it?

I'm going back to that chisel analogy though now and the microbevel is put on the wider bevel, which is the opposite to what you're doing? However that is single edged and different to a knife. In my case the apex is going to slightly favour the left hand side (but at a shallower angle in comparison I would assume than with your knife as i sharpen the right side at a lower angle) and so it probably would make more sense to microbevel the left hand side.

I'm curious because if I'm using the shallower angle on the right hand side (but the bevels are wider), would it be more beneficial to micro bevel both sides (smaller angles than I would if applying it to just the one side) compared to applying it to just one side? Looking back at that chisel again (and realising that my edge probably starts to resemble a chiselesque edge although not as extreme) I'm questioning whether I should be microbevelling the shallow angled and wider right bevel and then end up going round in circles.

Again thanks for the response. At this point I guess im obsessing over the details and I would probably benefit from trying your method on another knife just to compare differences
 
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To put it simply, I'd suggest that the micro-bevel on a gyuto is done in such a way that the very edge has roughly the same angle on the left side as the right - Remember: this is talking about the micro-bevel only, a small hairline of a thing. Doing it this way completely ignores (or has nothing to do with):
  • Centering the edge directly below the middle of the spine
  • How short or wide the bevels are on either side
  • Steering
  • Food release
The micro bevel is too small to really affect any of these.

We tend to do it on whichever side has the more acute bevel of the two, and in doing so builds more reinforcement behind whichever side has the shallower angle - generally the right side for a right handed asymmetry. This helps increase edge retention.
Remember, this only applies to a knife designed for mostly up and down work, perpendicular to a cutting board surface. As I mentioned earlier, this rule would reverse if you're dealing with a single bevel knife, or a double bevel that was designed to ride up accurately against a material or mark that you don't want to cut into.

Clear as mud? :p
 
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Alright sweet as, I was taking that approach originally and started over analysing it trying to figure out the principle of it all. Definitely have more confidence in what im doing now, cheers.
 
Interesting stuff! A couple questions:
1. Is half convex the way a 70/30 or other would come from from a manufacturer, or is this purely custom and/or done after purchase?
2. I hope i didn't miss it, but what is your preferred method for sharpening/creating the convex side?

Thanks!
 
DainBramage1 said:
1. Is half convex the way a 70/30 or other would come from from a manufacturer, or is this purely custom and/or done after purchase?
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It can be done many ways. Half convex, full convex, S-grinds, sabre grinds (wide bevels) and even concave grinds are all possible ways to get a 70/30. Manufacturers can use any of these, but will mostly use convex as it is the easiest to do.
Here's an example (from marc4ptoknives on Instagram) of a Tanaka Kyuzo Migaki. It has a 70/30 grind which is clearly not convexed, but instead a concave wide-bevel.
7ylvjyr.jpg


DainBramage1 said:
2. I hope i didn't miss it, but what is your preferred method for sharpening/creating the convex side?
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Slack belts are pretty boss for convex, but it can be done by hand on a stone too. Doing it well involves a lot of back and-forth-testing, for the first few times at least.

I should mention that its not a good idea to use the belt for sharpening... it's for doing the grind.
A kitchen knife which is properly thin behind the edge will have small edge bevels, so hand sharpening will only take a couple of minutes at most.
 
Kippington said:
It can be done many ways. Half convex, full convex, S-grinds, sabre grinds (wide bevels) and even concave grinds are all possible ways to get a 70/30.
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Thanks! One more question… can you think of any reasons not to turn a 50/50 (Tojiro DP 240mm) asymmetrical?
 
If you post a choil shot I can give you a decent answer.
Without it I'm kinda in the dark.
 
Kip - thanks for your diagrams, pictures and the wealth of knowledge in this thread. Awesome!

I have an asymmetrically ground and sharpened komakiri, its just a bit thick in general for me. The release is noticable, though
 
In the original post it mentions the edge being curved to reduce sticktion. If you've worn away a decent amount of your knife, how do you recreate an edge that is curved with stones? It would make a flat edge no?
 
stephen129 said:
In the original post it mentions the edge being curved to reduce sticktion. If you've worn away a decent amount of your knife, how do you recreate an edge that is curved with stones? It would make a flat edge no?
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There are a few ways to maintain convexity. One would be to rock the blade Murray Carter style. The other would be to use a worn down stone with a curve in it.
 
stephen129 said:
Ah, interesting. So is this how I should be thinning my knives? Or is it only of it had a convex grind to start with?
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Well, perhaps it depends on your goals. I like thin knives and do not care about convexity until the end of the process. Then I make sure there’s a nice convexity (for less wedging).
But if you want to restore original geometry as closely to the original as possible perhaps the wobble movement is the way to go?!
 
All depends. I use a version of Jon at JKI single bevel sharpening (hamaguri) for thinning and sharpening. But this convex way Murray Carter is doing is a viable option.
 
Carl Kotte said:
Well, perhaps it depends on your goals. I like thin knives and do not care about convexity until the end of the process. Then I make sure there’s a nice convexity (for less wedging).
But if you want to restore original geometry as closely to the original as possible perhaps the wobble movement is the way to go?!
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Unless you're using a very coarse stone and huge pressure convexity of the bevel comes almost by itself when different angles are being used. Blending requires only a single stroke. Facetting is only a problem with jig users. Check with your nail.
I apply Carter's rocking motion with some pressure on a charged rough split leather with a hard wooden backing. With simple carbons it contributes to the convexity. Stay behind the very edge. End with light edge stropping to clean up from the debris you have moved to it.
 
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Benuser said:
Facetting is only a problem with jig users.
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I assume this comment is about normal wide bevel sharpening or light thinning?

I did some major 2-angle thinning of the blade face (couple hours on an atoma 140 and Gesshin 400) on this Mizuno I have a couple weeks ago, and while there were no *sharp* facets at the end, I still felt the geometry was a bit more polygonal than I liked until I did a bunch of rocking strokes. Now it’s mind blowingly awesome.

Edit: I think I misread @Benuser’s first sentence as not applying to the rest of his post. So, +1 to everything he said, as usual.
 
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