# Thinning, Grinds, and Food Release



## jwthaparc (Jan 20, 2021)

So a recent thread got me thinking about food release a bit. What would the optimal grind to go for when thinning be? Convexed on both sides? Convexed on the right face flat on the left? Both flat? How convexed, if so? What difference does any of it make? 

I have heard convexity aids in food release, while I would imagine the flat grind will help you slide through ingredients with ease. So that brings me to the topic. 

What should a person go for if they want the best of both worlds?


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## tcmx3 (Jan 21, 2021)

depends on the rest of the knife.

in general convexity helps with release, yes. that said, my personal preference is for a knife to have some sort of concavity above the main flats, which I can then grind pretty much dead flat. I dont personally like maintaining or polishing heavily convexed knives, and my personal experience (and, I suppose, diet) allow for this. 

I do not like the true lazer style full flat ground knives at all. maybe it's my imagination but I imagine the shinogi, whether it's really a hard one or just where you run into the Kurouchi finish, gives you enough help to let you grind the rest of the knife in a way I personally enjoy.


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## panda (Jan 21, 2021)

asymmetric full convex. aggressive convex on release side, gentle convex on opposite side.


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## JDC (Jan 21, 2021)

I prefer Yoshikane's style - reasonably thick spine, aggressive high grind with very thin convex. Food release in most situations is good. Can occasionally create suction, but I'll take that given the superb performance. 

If maintenance is not a concern, double or triple hollow grind can be the best for both performance and food release.


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## Stef (Jan 21, 2021)

Just based on food release as far as I know an s-grind is the most effective and what to aspire to(depending on the knife).


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## Nemo (Jan 21, 2021)

I just try to maintain the existing geometry as much as possible.


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## Kawa (Jan 21, 2021)

This, and that other topic got me thinking about assymetry aswell...

I'd like to show a link. Please take a look at the choil shot.









Yu Kurosaki Shizuku SPG2 Hammered Bunka Japanese Knife 165mm Shitan Handle


Yu KurosakiWell known for his unique blade designs Yu Kurosaki is one of the youngest and most talented blacksmiths in Japan. Not only does Kurosaki tempt us with his beautiful blade designs, but their ability to perform keeps us coming back. High quality materials and age old forging techniques...




www.japanny.com





Does this make it a lefty knife?
Since if I turn it around and start cutting with my right hand, the flatter side is on the right/release side?


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## captaincaed (Jan 21, 2021)

Flat grinds don't always reduce friction either. They can have a suction cup effect at worst. A gentle convex/hamaguri grind can help wide bevels as well. There are shades of difference between full flat and full convex too. Those are some of my favorites.


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## Kippington (Jan 21, 2021)

Stef said:


> Just based on food release as far as I know an s-grind is the most effective


Gotta put as many curves and ridges on the surface as possible!


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## jwthaparc (Jan 21, 2021)

Kawa said:


> This, and that other topic got me thinking about assymetry aswell...
> 
> I'd like to show a link. Please take a look at the choil shot.
> 
> ...


Huh, it does look like the opposite of what I would be expecting for a right handed knife. Maybe it's the way it's being held that makes it seem to be more convexed on the left face.


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## jwthaparc (Jan 21, 2021)

Kippington said:


> Gotta put as many curves and ridges on the surface as possible!


I could see some problems appearing when doing maintenance on a knife with an s grind.


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## jwthaparc (Jan 21, 2021)

panda said:


> asymmetric full convex. aggressive convex on release side, gentle convex on opposite side.


Like aggressive enough to get rid of the shoulder of the bevel on the right?


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## Kawa (Jan 21, 2021)

jwthaparc said:


> Huh, it does look like the opposite of what I would be expecting for a right handed knife. Maybe it's the way it's being held that makes it seem to be more convexed on the left face.



Yeah, I thought of 'perspective' myself, but
The left side in the picure (or release side when cutting as righty) also seem to have a longer/higher flat.

Maybe someone knows this knife in real life?


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## Benuser (Jan 21, 2021)

jwthaparc said:


> Like aggressive enough to get rid of the shoulder of the bevel on the right?


Let the bevel form a continuous arc with the right face.
Here a very fat example, a yo-deba.


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## jwthaparc (Jan 21, 2021)

I went ahead and increased the convexity of my tojiro 210 shiro gyuto to an asymmetric convexed edge. It's a bit hard to tell because it does get quite thin just behind the edge. 




Here is the right face before polishing. I will add another pic to show the finished product.


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## JDC (Jan 21, 2021)

Looks a great job!


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## jwthaparc (Jan 21, 2021)

JDC said:


> Looks a great job!


Thank you!


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## jwthaparc (Jan 22, 2021)

And here it is off the kitayama, ready to go on the naturals.



Here it is after the uchigumori, it was a bit of a rushed job, but good enough. I will likely touch it back up later, or move to my tenjyou suita.


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## tcmx3 (Jan 22, 2021)

so I know I dont get the kudos of the full convex gang, but I do want to reiterate how great (relatively, I mean Im not sharpening on diamond plates here) flat bevels with concave flats can be. Im not going to say it's better, but if you've never tried it maybe take a look at the stuff coming out of Sanjo.

ease of maintenance doesnt hurt, either.


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## jwthaparc (Jan 22, 2021)

tcmx3 said:


> so I know I dont get the kudos of the full convex gang, but I do want to reiterate how great (relatively, I mean Im not sharpening on diamond plates here) flat bevels with concave flats can be. Im not going to say it's better, but if you've never tried it maybe take a look at the stuff coming out of Sanjo.
> 
> ease of maintenance doesnt hurt, either.


I'm just trying out what is available to me atm. I'm going to see how this full assymetrical convex goes. If I don't really like it, I can eventually back off the convexity. 

I wish I had enough cash to try a lot of the knives I see here. I dont know how expensive the knives you are recommending are though. I guess what I'm trying to say, is one day I will give those knives a try. It just might not be anytime soon.


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## JDC (Jan 22, 2021)

tcmx3 said:


> so I know I dont get the kudos of the full convex gang, but I do want to reiterate how great (relatively, I mean Im not sharpening on diamond plates here) flat bevels with concave flats can be. Im not going to say it's better, but if you've never tried it maybe take a look at the stuff coming out of Sanjo.
> 
> ease of maintenance doesnt hurt, either.


What do you do to make the flats concave?


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## tcmx3 (Jan 22, 2021)

JDC said:


> What do you do to make the flats concave?



well personally I dont.

the maker can though. several Sanjo area knives I own are like this; Mazaki, Hinoura, etc. even a cheap little Murata Funayuki I paid under 100 bucks for


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## JDC (Jan 22, 2021)

tcmx3 said:


> well personally I dont.
> 
> the maker can though. several Sanjo area knives I own are like this; Mazaki, Hinoura, etc. even a cheap little Murata Funayuki I paid under 100 bucks for


Now I wonder if they do this intentionally...


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## JaVa (Jan 22, 2021)

If there's a line of knives and they all have hollow grinds, it's pretty safe to assume it's designed that way. if there's a line of knives that only one or two or few are known to having hollow grinds and the rest don't have it, it's probably safe to assume it's by accident.

If some part of the shaping of the knife is done with a grinder by the maker, it can easily leave some concave shape by accident. Mostly though I believe it's there by design.

I really enjoy the concave/hollow grind when it's well done.


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## JaVa (Jan 22, 2021)

How do you guys see the term S-grind?

In conversations I see it's used in the same context as hollow/concave grinds quite a lot. And it does kinda fit as it kinda does make the S shape and maybe that's even an accurate assessment. but to me S-grind would be more like what Dalman does, when a hollow/concave part starts after the "primary" edge grind and that makes the S Shape in the grind. If that makes sense.

Also does it matter if the initial grind behind the edge is hollow or flat or convex. If after that there's a concave grind (Dalman style). Would it still be an S-grind?


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## JDC (Jan 22, 2021)

JaVa said:


> How do you guys see the term S-grind?
> 
> In conversations I see it's used in the same context as hollow/concave grinds quite a lot. And it does kinda fit as it kinda does make the S shape and maybe that's even an accurate assessment. but to me S-grind would be more like what Dalman does, when a hollow/concave part starts after the "primary" edge grind and that makes the S Shape in the grind. If that makes sense.
> 
> Also does it matter if the initial grind behind the edge is hollow or flat or convex. If after that there's a concave grind (Dalman style). Would it still be an S-grind?



To me where to put the hollow and how many hollows to put is the question. I don't think the convex part in an S-grind is necessary from a purely performance point of view. Dalman did replace the convex grind behind the edge with concave grind on some of his knives. This dramatically increases the laserish cutting feel while the food release can be as good, if not better. 

The problem is maintenance: how do you thin the knife? how much food release is left after consecutive thinning? Seems to be a dilemma.


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## jwthaparc (Jan 22, 2021)

Yeah, one thing I remember Carter saying makes a good knife is the ability for it to be maintained by the user. He made that statement arguing against serated knives (in most cases), but I can see it fitting here.


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## ModRQC (Jan 22, 2021)

tcmx3 said:


> well personally I dont.
> 
> the maker can though. several Sanjo area knives I own are like this; Mazaki, Hinoura, etc. even a cheap little Murata Funayuki I paid under 100 bucks for



Hmmmm... Concave grind I don't see with Mazaki, nor Hinoura. Murata those I saw were heavily asymmetrical wide bevels, Hinoura does wide bevels, Mazaki is pretty convexed/shoulders rounded but still mostly a wide bevel - can distinctively see the planes in a choil shot. Some level of asymmetry for those two as well but nothing like that of Murata. Sanjo are not really known for doing concave, but for doing thick at the spine convex grinds.

Those who affectionate a good deal of concavity I know of offhand are Y. Kato and Kurosaki - most grinds I've seen.


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## ModRQC (Jan 22, 2021)

Also lasers do tend to present slight convexity - Kono HD2, Takamura for example. No V-grinds there.


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## tcmx3 (Jan 22, 2021)

ModRQC said:


> Hmmmm... Concave grind I don't see with Mazaki, nor Hinoura. Murata those I saw were heavily asymmetrical wide bevels, Hinoura does wide bevels, Mazaki is pretty convexed/shoulders rounded but still mostly a wide bevel - can distinctively see the planes in a choil shot. Some level of asymmetry for those two as well but nothing like that of Murata. Sanjo are not really known for doing concave, but for doing thick at the spine convex grinds.
> 
> Those who affectionate a good deal of concavity I know of offhand are Y. Kato and Kurosaki - most grinds I've seen.



I dunno what to say man. If I go pick up either my own Mazaki or Hinoura the flats above the bevels are distinctly not flat, but concave. On the Hinoura especially it's so noticeable as to be visible.

actually my Hinoura has some concavity on one of the bevels too but that appears to be more of a rushed grinding job than intentional lmao. not that it matters to me for <250 dollars

I should note for clarity Im talking about this bit here


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## JDC (Jan 22, 2021)

tcmx3 said:


> I dunno what to say man. If I go pick up either my own Mazaki or Hinoura the flats above the bevels are distinctly not flat, but concave. On the Hinoura especially it's so noticeable as to be visible.
> 
> actually my Hinoura has some concavity on one of the bevels too but that appears to be more of a rushed grinding job than intentional lmao. not that it matters to me for <250 dollars
> 
> ...


Ah, the hammered finish is a different story, and the ridges can still be problematic...


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## spaceconvoy (Jan 22, 2021)

jwthaparc said:


> Yeah, one thing I remember Carter saying makes a good knife is the ability for it to be maintained by the user. He made that statement arguing against serated knives (in most cases), but I can see it fitting here.


This has become more important to me over the years. You can spend $$$ chasing the perfect grind from a maker, but then what? If you're a home user you can maybe get away with babying it for a year to preserve ootb performance. Seems like a good number of people here will just buy another knife at that point, or well before then - are they really 'bored' with the knife or just noticing the subtleties of degraded geometry?

It's not the optimal geometry for food release, but I prefer a symmetrical convex grind. Combined with a polished blade and self-applied 800 grit sandpaper 'hairline' finish, I can maintain close-to-ideal performance and aesthetics indefinitely. Not worrying about scratches during use or avoiding thinning while sharpening allows me to use the knife as a tool instead of a sacred object.

To achieve the perfect convex grind just buy a knife that's thicker than ideal and regrind it yourself. I've found that Sukenari has what I'm looking for, a nicely convex middleweight that just slightly too wedgy ootb. Spend $5 on a bag of small apples from the grocery store and check the balance between wedginess and food release periodically while thinning. That's how I've found my ideal geometry.


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## stringer (Jan 22, 2021)

I am still not exactly sure what you all are cutting up that causes you such issues. 

In my opinion, if you don't like the way food is releasing from your knife then you have two options. 
1. Think about using a different tool to complete the task at hand (a mandoline or food processor attachment is sometimes just the way to go and that is okay)

2. Modify your knife by adding convexity to improve its food release (any knife, not just big tall fat ones)

Here's a video showing what I mean


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## jwthaparc (Jan 22, 2021)

stringer said:


> I am still not exactly sure what you all are cutting up that causes you such issues.
> 
> In my opinion, if you don't like the way food is releasing from your knife then you have two options.
> 1. Think about using a different tool to complete the task at hand (a mandoline or food processor attachment is sometimes just the way to go and that is okay)
> ...



Weird apple indeed.


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## captaincaed (Jan 23, 2021)

spaceconvoy said:


> This has become more important to me over the years. You can spend $$$ chasing the perfect grind from a maker, but then what? If you're a home user you can maybe get away with babying it for a year to preserve ootb performance. Seems like a good number of people here will just buy another knife at that point, or well before then - are they really 'bored' with the knife or just noticing the subtleties of degraded geometry?
> 
> It's not the optimal geometry for food release, but I prefer a symmetrical convex grind. Combined with a polished blade and self-applied 800 grit sandpaper 'hairline' finish, I can maintain close-to-ideal performance and aesthetics indefinitely. Not worrying about scratches during use or avoiding thinning while sharpening allows me to use the knife as a tool instead of a sacred object.
> 
> To achieve the perfect convex grind just buy a knife that's thicker than ideal and regrind it yourself. I've found that Sukenari has what I'm looking for, a nicely convex middleweight that just slightly too wedgy ootb. Spend $5 on a bag of small apples from the grocery store and check the balance between wedginess and food release periodically while thinning. That's how I've found my ideal geometry.


Man I love this thought. "Goodness over time" is my new goal instead of "perfect today." Well said.


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## DavidPF (Jan 25, 2021)

I've studied the knife I have now, according to what's being said here, and I have a strong feeling that I know exactly how it was made. Except for the edge's curve up to the tip and the spine's curve down to the tip, the entire knife from the bolster forwards appears to be literal straight lines from point to point, programmed into a CNC machine. My knife is a real-life build of an unmodified schematic diagram. The manufacturers never bothered to turn to "Chapter 2: Grinds" in their "How To Knife" textbook, so it's a wedge grind with a wedge-shaped distal taper. I can say it's entertaining to look at, imagining the generations of accumulated knowledge and experience that this blade has nothing whatsoever to do with.

I bought it because I needed a knife. 

Now I have it, and I've discovered I still need a knife.


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## stringer (Jan 25, 2021)

DavidPF said:


> I've studied the knife I have now, according to what's being said here, and I have a strong feeling that I know exactly how it was made. Except for the edge's curve up to the tip and the spine's curve down to the tip, the entire knife from the bolster forwards appears to be literal straight lines from point to point, programmed into a CNC machine. My knife is a real-life build of an unmodified schematic diagram. The manufacturers never bothered to turn to "Chapter 2: Grinds" in their "How To Knife" textbook, so it's a wedge grind with a wedge-shaped distal taper. I can say it's entertaining to look at, imagining the generations of accumulated knowledge and experience that this blade has nothing whatsoever to do with.
> 
> I bought it because I needed a knife.
> 
> Now I have it, and I've discovered I still need a knife.



You can fix it. There are no perfect knives. You only really need the convexity in the 10mm behind the edge. Start thinning so you are hitting 10mm behind the edge consistently and then gradually move the focus of your finger pressure toward the edge. Deburr at a little higher angle yet. And you will add convexity where the knife really needs it. This also makes sure you get rid of any factory shoulders. All of my knives get this treatment. I never have issues with food release or wedging.


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## JaVa (Jan 25, 2021)

...But but but, I have the perfect knife?
...For me!

Wakui Hairline, It's like it was built for me. Everything about that knife is like someone asked me what I want from a knife and then made it. Profile, grind, weight, balance, f&f, heel hight, tip, thinness behind the edge food release, performance, it all is blends into a perfect knife for me. And for 200€??? You gotta be kidding me!

Except the steel. It's great for White 2 (not my preferred steel), but SKD would be better. But in this thread we're not talking about the steel, we're discussing thinning, grinds and food release and that's where it shines for me.

Edit. Thank you Preizzo!


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## ModRQC (Jan 25, 2021)

stringer said:


> You can fix it. There are no perfect knives. You only really need the convexity in the 10mm behind the edge. Start thinning so you are hitting 10mm behind the edge consistently and then gradually move the focus of your finger pressure toward the edge. Deburr at a little higher angle yet. And you will add convexity where the knife really needs it. This also makes sure you get rid of any factory shoulders. All of my knives get this treatment. I never have issues with food release or wedging.



Could you still manage to do that you think with a knife that's quite thin behind the edge OOTB, but with a sticky laser-ish V grind? Since you don't have tons of steel to play around, it seems difficult. Not that I'd know of another way for these. I usually worked on knives that needed the thinning to start with. Always used compound bevels as the technique I learned first and know how well, but always wondered with differential pressure points and levels to create convexity on very thin edges... Thanks for any further insight!


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## jwthaparc (Jan 25, 2021)

ModRQC said:


> Could you still manage to do that you think with a knife that's quite thin behind the edge OOTB, but with a sticky laser-ish V grind? Since you don't have tons of steel to play around, it seems difficult. Not that I'd know of another way for these. I usually worked on knives that needed the thinning to start with. Always used compound bevels as the technique I learned first and know how well, but always wondered with differential pressure points and levels to create convexity on very thin edges... Thanks for any further insight!


I would use a slightly higher grit, so you are removing the metal slower. It will help you make sure you ate doing exactly what you want with the precious little steel you have to mess around with.


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## ModRQC (Jan 25, 2021)

jwthaparc said:


> I would use a slightly higher grit, so you are removing the metal slower. It will help you make sure you ate doing exactly what you want with the precious little steel you have to mess around with.



That's for sure. Still when already needle like behind the edge there's little room for anything but convexing at the very edge a bit, which I suspect won't make a world of difference if any.


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## jwthaparc (Jan 25, 2021)

ModRQC said:


> That's for sure. Still when already needle like behind the edge there's little room for anything but convexing at the very edge a bit, which I suspect won't make a world of difference if any.


I think it may actually help a bit. It won't make it worse at least.


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## ModRQC (Jan 25, 2021)

Nope and interesting to try! I never truly met such a knife - usually those cheap V grinds aren't particularly thin behind. More of a theoretical wonder.


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## stringer (Jan 25, 2021)

ModRQC said:


> Could you still manage to do that you think with a knife that's quite thin behind the edge OOTB, but with a sticky laser-ish V grind? Since you don't have tons of steel to play around, it seems difficult. Not that I'd know of another way for these. I usually worked on knives that needed the thinning to start with. Always used compound bevels as the technique I learned first and know how well, but always wondered with differential pressure points and levels to create convexity on very thin edges... Thanks for any further insight!



Yes, I believe that a lot of the benefits of convexity don't require a thick blade or extra wide bevels. If you a have laserish knife with a very flat v-grind (I give the Kanehide as an example) you can add convexity to it and improve food release by thinning behind the edge, getting rid of the factory shoulders, convexing the path to the apex, and applying some form of a microbevel/high angle pass/kippington style deburr to finish.

You strop a straight razor to smooth out the teeth, but partly to add some micro-convexity as well. Here the goal isn't food release but the idea of allowing the blade to glide over the skin and cut the hair but not the skin is done through essentially micro-convexing with the strop. 

Micro-convexing will not have the same affect as all of the crazy versions of s-grinds and such, but it can really make a difference. And for knives that are chippy because their bevel angle is too small, adding a little micro-convexing can be enough to strengthen the bevel without having to do a full on more traditional micro-bevel.


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## DavidPF (Jan 25, 2021)

stringer said:


> You can fix it. There are no perfect knives. You only really need the convexity in the 10mm behind the edge. Start thinning so you are hitting 10mm behind the edge consistently


I should say (if it wasn't clear) that this is a supermarket knife.

I may just have a poor grasp of what you're saying, because my mind often fails to draw 3D pictures correctly, but I think maybe I do know what you're saying and actually don't get how it could work. If there was a choil shot of this knife (there's a fat bolster in the way), the entire choil shot including the spine would literally be one continuous wedge, a plain unrelieved V - there is no surface at a right angle to the spine _anywhere_, no concave area, no convex area, just wedge. If I aimed to hit 10 mm above the edge, I would necessarily also hit the spine at the exact same time, and regrind the entire surface.

I theoretically could gouge that 10 mm zone near the edge so that part of the knife becomes a narrower wedge than the rest... ? In my hands, this would just take it from Probably Bad, to Embarrassingly Bad And Ugly Too.


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## stringer (Jan 25, 2021)

DavidPF said:


> I may just have a poor grasp of what you're saying, because my mind often fails to draw 3D pictures correctly, but I think maybe I do know what you're saying and actually don't get how it could work. If there was a choil shot of this knife (there's a fat bolster in the way), the entire choil shot including the spine would literally be one continuous wedge, a plain unrelieved V - there is no surface at a right angle to the spine _anywhere_, no concave area, no convex area, just wedge. If I aimed to hit 10 mm above the edge, I would necessarily also hit the spine at the exact same time, and regrind the entire surface.
> 
> I theoretically could gouge that 10 mm zone near the edge so that part of the knife becomes a narrower wedge than the rest... ? In my hands, this would just take it from Probably Bad, to Embarrassingly Bad And Ugly Too.




Oftentimes the things necessary to improve performance do not add a whole lot to the aesthetic value of the knife.


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## tostadas (Jan 25, 2021)

DavidPF said:


> I should say (if it wasn't clear) that this is a supermarket knife.
> 
> I may just have a poor grasp of what you're saying, because my mind often fails to draw 3D pictures correctly, but I think maybe I do know what you're saying and actually don't get how it could work. If there was a choil shot of this knife (there's a fat bolster in the way), the entire choil shot including the spine would literally be one continuous wedge, a plain unrelieved V - there is no surface at a right angle to the spine _anywhere_, no concave area, no convex area, just wedge. If I aimed to hit 10 mm above the edge, I would necessarily also hit the spine at the exact same time, and regrind the entire surface.
> 
> I theoretically could gouge that 10 mm zone near the edge so that part of the knife becomes a narrower wedge than the rest... ? In my hands, this would just take it from Probably Bad, to Embarrassingly Bad And Ugly Too.



I doubt that its a true flat grind from the apex to the spine. If that were the case, then there is not really anything you could do to thin. More likely, its fairly flat until 1-2mm behind the very edge, where you have your primary bevel. I could be wrong, but it would help if you had a photo of the edge.


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## DavidPF (Jan 25, 2021)

tostadas said:


> I doubt that its a true flat grind from the apex to the spine. If that were the case, then there is not really anything you could do to thin. More likely, its fairly flat until 1-2mm behind the very edge, where you have your primary bevel. I could be wrong, but it would help if you had a photo of the edge.


My photo skills are terrible, but I just verified that it is lay-a-straightedge-on-it-no-daylight flat. (Until the rolling sharpener's edge kicks in )

Note: I thought "maybe my straightedge wasn't straight", so I found the straightest thing in the house, the edge of a new 50-mm-length Japanese disposable razor blade, and the knife really is flat flat right to the edge.


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## tostadas (Jan 25, 2021)

DavidPF said:


> My photo skills are terrible, but I just verified that it is lay-a-straightedge-on-it-no-daylight flat. (Until the rolling sharpener's edge kicks in )



But like stringer said, there is still a bevel at the very end of the knife. You can create your convex from apex to 10mm, because currently it should not be flat between those two points.


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## ian (Jan 25, 2021)

Even if the grind is totally flat, it’s completely possible to add convexity. If you want a lot of it, you can start sharpening with a super low angle, like 1 degree more than flat. That’ll decrease the height of the knife, but it’ll also cut in a new bevel, which will give you some convexity.

But if you want just a bit of convexity, which you probably do, remember that metal is removed primarily where pressure is applied. So if you put the whole flat grind right on the flat stone, it’s true that you’ll scratch up the whole knife, but if you keep your finger pressure near the edge, you’ll remove more material there, slowly converting the flat grind into a convex one.


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## DavidPF (Jan 25, 2021)

tostadas said:


> But like stringer said, there is still a bevel at the very end of the knife. You can create your convex from apex to 10mm, because currently it should not be flat between those two points.


I'm confused by this - the current non-flat area (bevel) is around 1 mm. It is just like the example pictures given with "don't skip thinning behind the edge, or this is what you'll get".


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## tostadas (Jan 25, 2021)

DavidPF said:


> I'm confused by this - the current non-flat area (bevel) is around 1 mm. It is just like the example pictures given with "don't skip thinning behind the edge, or this is what you'll get".







I assume the black is what your blade looks like. Red is where you can apply a slight convex from apex to 10mm


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## DavidPF (Jan 25, 2021)

ian said:


> if you keep your finger pressure near the edge, you’ll remove more material there, slowly converting the flat grind into a convex one.


This makes sense to me - something like this would be messy and approximate at first, and gradually take better shape. It's asymptotic, or some other related cute term.

Well, a scratched-up but somewhat improved knife will be worth it, and if it ends up scratched-up and also worse, it's no great loss.


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## DavidPF (Jan 25, 2021)

tostadas said:


> I assume the black is what your blade looks like. Red is where you can apply a slight convex from apex to 10mm


Thank you, you are exactly right and this makes perfect sense.


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## tostadas (Jan 25, 2021)

DavidPF said:


> Thank you, you are exactly right and this makes perfect sense.


Just try to do it flat from apex to 10mm. Slight inconsistency from hand sharpening coupled with stones that may not be completely flat will naturally make it convex.


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## stringer (Jan 25, 2021)

It's really more about finger pressure than angle precision. Here's a thread I did where I show how I approach it.






sharpening with continuously changing bevel


I made a video of my sharpening routine. This is a demonstration of starting with the tip at a zero bevel and ending with the heel third at about 22 degrees per side. This creates a continuously variable "wide bevel". I start off with the tip flat on the stone. This helps me to keep thinning the...




www.kitchenknifeforums.com


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## DavidPF (Jan 25, 2021)

tostadas said:


> Just try to do it flat from apex to 10mm. Slight inconsistency from hand sharpening coupled with stones that may not be completely flat will naturally make it convex.


I have enough inconsistency to cause not just convex but pear-shaped.  But I'll try it.


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## M1k3 (Jan 25, 2021)

ModRQC said:


> Could you still manage to do that you think with a knife that's quite thin behind the edge OOTB, but with a sticky laser-ish V grind? Since you don't have tons of steel to play around, it seems difficult. Not that I'd know of another way for these. I usually worked on knives that needed the thinning to start with. Always used compound bevels as the technique I learned first and know how well, but always wondered with differential pressure points and levels to create convexity on very thin edges... Thanks for any further insight!


Yes. I've done it on a Takamura.


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## ModRQC (Jan 25, 2021)

M1k3 said:


> Yes. I've done it on a Takamura.



Lol man exactly the knife I had in mind to buy and try. Thanks!


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## SeattleB (Jan 26, 2021)

As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.


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## tostadas (Jan 26, 2021)

SeattleB said:


> As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.


Don't know about the science behind it, but it's definitely noticable. I can confirm that fractions of a mm behind the edge have a considerable difference in performance. Your calculation example is not exactly accurate because in reality the thickness of a "flat ground" knife from spine typically does not go from 2mm down to 0. But rather probably something like 2mm down to 1mm (and then a very abrupt angle change at the very end).

At 10mm behind the edge, I would consider anything 1.1mm or under to be pretty thin, assuming that it goes down to around 0.2mm @ 1mm behind the edge.


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## stringer (Jan 26, 2021)

SeattleB said:


> As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of conductivity will be measured in fractions of a millimeter. How does this help with food release? It would seem to this newbie that the amount of convexity would have to be more than that.



I don't add convexity to improve food release. I do it because I like my knives to be as thin behind the edge as possible for the task at hand. I dislike harsh shouldered bevels and zero bevels are too fragile. A convex edge is easy to maintain (except for maybe aesthetically) and is the best of both worlds. Plus, when you get used to sharpening this way you can adjust bevel angle on the fly and make the tip really pointy and the choil really stout. The fact that food release is also improved is just an added bonus. I used to think you need a thick spined wide bevel knife to enjoy the benefits, but now I believe that you can sharpen even the thinnest lasers this way.


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## jwthaparc (Jan 26, 2021)

SeattleB said:


> As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.


You would be surprised. I mean if you go up to the choil shot I did if my tojiro gyuto, that thing is very thin behind the edge. Having the little convexity that is there makes all the difference.

It's like someone with an untrained eye looking at a very different gyutos and thinking they are pretty much the same knife because they dont look that different. when in reality the small details are what make them different from each other.


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## ian (Jan 26, 2021)

SeattleB said:


> As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.



The knife will probably be thicker than that. .4mm at 10mm behind the edge is not a realistic measurement. You should expect .8-1mm thick at 10mm from the edge. .5mm at 5mm from the edge.

That said, it doesn't take a lot of convexity to make a difference, in terms of food release, in terms of the amount of sticking you feel as you cut, and in terms of edge stability.


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## stringer (Jan 26, 2021)

Here's another thread where you can see some pictures of what a convex grind looks like compared to a typical factory microbevel. This knife was generally left on a prep table for anyone to use at a busy hotel for 12 hours a day for three years. 

I also show how I start converting the factory flat grind into something more convex.






Old Beater Meet New Beater


You know that feeling when you start getting bruises and cuts on your knuckles because you're favorite beater has been sharpened too many times? What can it mean? Only one thing. New knife day. Kanehide TK 240 3 years old vs new.




www.kitchenknifeforums.com


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## KKL81 (Jan 26, 2021)

SeattleB said:


> As a newbie, I'm a little unclear on this concept. We start with a 50mm tall knife with a 2mm spine that has a truly flat grind down to the edge. Then we're going to round the last 10mm to get convexity. It seems the amount of convexity will be measured in fractions of a millimeter. After all, how thick is the knife 10mm back from the edge? (Quick check with a calculator shows the knife would be 0.4mm thick). How much convexity can we put in that last 10mm? It would seem to this newbie that the amount of convexity would have to be more than that to affect food release.



Assuming that a crappy knife will be like 0.75mm thick behind the edge, your numbers gives 1mm thickness 10mm behind the edge and 0.875mm at 5mm. Just keep the 1mm, thin the 0.875mm to 0.5mm and the 0.75mm to 0.1, no problem.


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