You can see in the Wat picture the concavity is a hollow cut into the bottom third of the knife. It's slightly less pronounced now than when I got it because it has been used and sharpened a ton.
A q. about convex grinds
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You can see in the Wat picture the concavity is a hollow cut into the bottom third of the knife. It's slightly less pronounced now than when I got it because it has been used and sharpened a ton.
OK, that's helpful, thank you. Sounds a little like an ura, a little like a one-sided S-grind.
Man, I really want to go grind a bunch of mild steel and cut potatoes just to convince myself how this stuff works
Man, I really want to go grind a bunch of mild steel and cut potatoes just to convince myself how this stuff works
My ashi ginga sujihiki basically has a ura. One side of the knife is full convex and the other is essentially full concave. Food release is very good for a laser slicer.
Yeah I remember seeing that with all the grind marks. Persuasive visual.
I personally find myself a little color-blind to choil pics, but scratch patterns, feeling it, or seeing a blade-road reflection in front of mini-blinds are pretty informative.
I personally find myself a little color-blind to choil pics, but scratch patterns, feeling it, or seeing a blade-road reflection in front of mini-blinds are pretty informative.
@stringer and others, your explanation makes total sense so I got that right. But if I take your Wat choil shot and rotate it 180 to simulate cutting position, the bevel/convex is on the food side, correct? (Unless you're a lefty)(or unless I am missing something or misreading the shot).
So that is what confuses me.
So that is what confuses me.
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Which food side? Cut or whole?
Ah, the Wat is fairly complex. I guess your sketch is more clear. Whole food in your left hand, right?
Just to be sure, the bevel is for food release, not the slight convexing on the other face.
Sorry to drag this along! Just want to make sure I am getting this right.
Understanding this helps reading choil shots on B/S/T!
Just to be sure, the bevel is for food release, not the slight convexing on the other face.
Sorry to drag this along! Just want to make sure I am getting this right.
Understanding this helps reading choil shots on B/S/T!
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sorry...had to
I don't think that that would have much affect on food release but it would help to reduce wedging in very tall hard stock like sweet potatoes.
I made a video to explain a little better because I am procrastinating. Ignore the fact that I write lefthanded and trust me that I am righthanded.
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I tried that. When a knife has a flat grind on either side, you can add convexing by grinding away the edge or thinning the spine. Thinning the spine is ok, when I want the convex behavior but don't want to remove metal from the edge. Would I do it normally? I dunno. It's good when you want the more food release. I know widebevels are sometimes thicker in the mid section compared to the spine. It was not uncommon for me to see the spine being thinner than the midsection or shoulder on a couple knives I've seen or used.
I mean, even the Kurouchi shihans have this somewhat but in a different way, with the spine being a bit thinner than due to the kurouchi indentation.
Jason183
Senior Member
I agreed, I still missed the cutting feel of Kanehiro gyuto I had before made by Yoshimi Kato, it was asymmetric grind, 3mm spine but outperformed most around 2mm spine lasers on carrots.
I’m always wondering is it possible to achieve the concave grind with the free hand sharpening? Or you have to do it with specific machine grinder?
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I mean, you can wrap some sandpaper around something round and go to town. Or get some EDM stones.
https://www.kitchenknifeforums.com/threads/hand-sandpapering-in-some-concavity.46427/
But probably noone does that, except when they're f**king around and don't know any better. Real knife makers make the concave grinds on a wheel.
Jason183
Senior Member
One of my Yoshikazu Tanaka wide bevel have that slight concave grind, I know one day it will become flat overtime with regular sharpening, really curious to know if there ways to maintain that concavitysomeone needs to invent a small wheel grinder for home use.
I think the more practical solution is to turn it convex once it gets too flat. One problem is that if you want a fully concave wide bevel you probably need to be working on a sizeable wheel. A small radius wheel will give you concavity, but a deep spindly strip of it rather than a slight concavity over the width of the bevel. But absolutely, more power tools at home. I gotta figure out what to buy next. I only own a stupid little 1x30 right now.
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Anything is possible. It's not something I would consider putting the time into trying to figure out. Like Ian said, Watanabe does the concavity really well. On most of my knives if the bevels are concave it's usually something I am trying to fix (like on that nakiri). I don't need concavity on that side. I am happy with just a really flat wide bevel with some convexity built in right behind the edge. I have not used any s-grinds and such, but they are basically taking the Watanabe grind even a step further. But I think they mostly use 2X72's with contact wheels.
This is a pretty good visual of what you’re thinking - more aggressive convexity on the right side vs the left side (blade-down). It’s pretty obvious from this choil shot with the core steel visible as a straight line reference. Just from eyeballing, it looks like most of the right-side convexity happens just a bit lower than the middle third of the blade, while the left side is fairly straight.
This is interesting. I see the kind of grind in your first drawing there a fair bit on the knives I work with (mostly Tosa blades). Initially I didn't think it was intentional, but they're always right hand bias, as in your pic, so I'm beginning to think perhaps it might be. It's normally very subtle indeed, though there have been a couple that I've had to check to make sure people aren't lefties before sending.
I also see similar-ish on caidao quite a lot. This pic exaggerates the effect, but you can see how the same sharpening angle, results in different edge angles:
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that's a really nice right handed grind. what do the bevels look like?
I believe that the hollows on the tosa knives are definitely intentional and the ones near the spine are forged in. I have wore away the kurouchi on mine quite a bit and you can tell that there is a lot of forging to shape being done, especially where the tang meets the meat of the knife on both sides. There's a ridge they leave thicker for support but then the hollow is hammered in for food release, nimbleness, and anti-wedging. The bevels are very slightly and subtly but definitively concave (at least on my sample of 1). It took several rounds of sharpening with tons of pressure on very aggressive stones to get them to flat. I agree with you on the Chinese style cleavers. Even on very thin ones you will see this kind of basic idea for geometry.
When new they were typical 50/50 small bevel. I’ve been sharpening at 8 degrees on the right side and 16 on the left just for practice (I haven’t experienced steering issues). This is a Shiro Kamo R2 btw.
Thanks, this is excellent! I was focusing on the sharp bevel thinking that was the sliced food releaser. And I overlooked the fairly subtle convexity that is actually the sliced food releaser.
Based on my own knives I assumed incorrectly one needed an explicit bevel (Munetoshi KU, TF Mab) or strong lower half convexing to achieve satisfactory sliced food release.
Never considered the held food release aspect.
I now too see that over the height of the blade there are more options for shaping than just bevels. Very informative!
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Interesting vid, I'd never really looked too hard / thought about the top. But have just checked mine and they do all seem to have that slight concavity making them a smidge fatter in the middle. They're not quite as pronounced as yours appears, though that might just be the vid. The bevels I have are largely straight to my eye (sometimes with some convexity to them). I can't see any that have hollow grinds on the bevels, though I've never taken one to stones in that way, it'd be interesting to try and see whether what I see as straight might actually be slightly concave.
Just checked my Kikuichimonji nakiri. And I now recognize the same choil profile. I always thought the blade was just a bit wonky (I did look at the choil before!) but didn't mind because it was so pleasant and had such nice food release. So now I understand this was made this way intentionally...
(feeling stupid).
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Seem to be missing the point when comparing a western double bevel deba vs a gyuto.
a thin behind the edge western deba will slice well but be more Prone to edge damage when used forwestern deba tasks.
pretty sure I know where the text is from and I’d put it down to this being more of a workhorse gyuto, than being a deba.
would those comparing it to a kato use their kato like a western deba?
a thin behind the edge western deba will slice well but be more Prone to edge damage when used forwestern deba tasks.
pretty sure I know where the text is from and I’d put it down to this being more of a workhorse gyuto, than being a deba.
would those comparing it to a kato use their kato like a western deba?
This is certainly what I was getting at originally, yep! Though it didn't sound like WH Gyuto; dimension-wise it's deba-ish: 150mm, 6mm spine, 54mm height. (Obviously I haven't seen the choil / grind though!)
I've never had a Kato. But I use all my knives like western debas, so if I get one someday I'll definitely try it.
Jason183
Senior Member
Now I’m using a blue#2 270mm gyuto for all kind of abusive tasks liked this, 3mm spine, I sharpened it at high angle to the point where been pretty much chip resistance, and it’s still sharper than Tojiro western deba I had also much easier to sharpen. The steel also matters, for chip resistance steel liked Aus-8, Aeb-L can go very thin behind the edge, even thinner than Kato without worrying about chipping.
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VICTOR J CREAZZI
Senior Member
Ha! I've been slowly converting an old clever to an S-grind by using it to take the dish out of stones when that is needed. In other words, I lap down the high ends of dished stones in the hollow of the S grind. When the stone gets closer to flat I go to SiC on granite.
It's slow going, but I need to rub the high spots of the stone on something anyway. Two birds with one stone.
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