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Totally agree with @ethompson. “Removing high spots” or “evening out the bevel”are more accurate than “flattening” when you’re not creating a bevel that’s completely flat. Although if you create a more or less flat bevel and then give it a bit of convexity at the end, the beginning part could be called flattening.

I also wonder whether the main reason that removing high spots improves performance is that the knife gets thinner. I bet that’s more of a factor than the fact that the grind is getting more regular, although I’m sure you can feel that a bit too.
My understanding about how a even and good shape, made with stones or other tools (but hard to beat stones for that work), can make a knife perform better is not really about thinning.
I think it is more about friction : for creating two evenly shaped bevels, first you need to straighten the blade (already there will be less friction with a straight blade versus a bent or warped blade). Then you will grind high spots : small or large surface were there is too much material, in relation of the lower point of the bevel ; doing so you erase hills and valeys, you even, you straighten by grinding : again you will get less friction.
Then you can create some convexity. Why is it good ? Because of friction again I think. Instead of having the all surface of the bevel in contact with food on a flat bevel, a convex surface will have less surface in contact, and so less friction.
Then of course, if you have all this but you're thick behind the edge, it won't cut great, so yeah, you should thin behind the edge too while you even you're bevel :)
 
My understanding about how a even and good shape, made with stones or other tools (but hard to beat stones for that work), can make a knife perform better is not really about thinning.
I think it is more about friction : for creating two evenly shaped bevels, first you need to straighten the blade (already there will be less friction with a straight blade versus a bent or warped blade). Then you will grind high spots : small or large surface were there is too much material, in relation of the lower point of the bevel ; doing so you erase hills and valeys, you even, you straighten by grinding : again you will get less friction.
Then you can create some convexity. Why is it good ? Because of friction again I think. Instead of having the all surface of the bevel in contact with food on a flat bevel, a convex surface will have less surface in contact, and so less friction.
Then of course, if you have all this but you're thick behind the edge, it won't cut great, so yeah, you should thin behind the edge too while you even you're bevel :)
This makes sense in general except if you now took these perfectly formed bevels and created low spots by grinding, you could decrease friction for all materials that are not soft enough to follow the surface exactly. For most ingredients such uneven bevels would have less contact with the surface of the blade. Hollow grind is an extreme example of this.
 
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This makes sense in general except if you now took this perfectly formed bevels and created low spots by grinding, you could decrease friction for all materials that are not soft enough to follow the surface exactly. For most ingredients such uneven bevels would have less contact with the surface of the blade. Hollow grind is an extreme example of this.

Ya, this was basically my point. If anything, you’ll probably decrease friction while cutting (hard ingredients, at least) if you take a nice convex grind and grind grantons into it. So measuring how even the grind is isn’t necessarily the point. In general, if the concavities in a blade are small enough so that the product you’re cutting mostly stays out of them, the cutting feel is probably pretty similar to what it’d be if you filled in the concavities. Maybe a bit less friction with the concavities, maybe more suction effects or things I’m not qualified to talk about.

Anyway, the point I was making about evening out bevels is that you don’t fill in low spots, you take out the high spots. So unless you decrease the height a bunch, the thickest parts of the knife are getting thinner, which seems to me like the thing that’s going to improve cutting performance the most.

That said, fixing more global imperfections, like straightening it, def makes a difference. Good point, @ethompson. And the cutting feel is prob a bit smoother if there are no bigger hills and valleys.
 
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Someone mention bevel shapes?
IMG-20220822-WA0003.jpg
 
Ya, this was basically my point. If anything, you’ll probably decrease friction while cutting (hard ingredients, at least) if you take a nice convex grind and grind grantons into it. So measuring how even the grind is isn’t necessarily the point. In general, if the concavities in a blade are small enough so that the product you’re cutting mostly stays out of them, the cutting feel is probably pretty similar to what it’d be if you filled in the concavities. Maybe a bit less friction with the concavities, maybe more suction effects or things I’m not qualified to talk about.

Anyway, the point I was making about evening out bevels is that you don’t fill in low spots, you take out the high spots. So unless you decrease the height a bunch, the thickest parts of the knife are getting thinner, which seems to me like the thing that’s going to improve cutting performance the most.

That said, fixing more global imperfections, like straightening it, def makes a difference. Good point, @ethompson. And the cutting feel is prob a bit smoother if there are no bigger hills and valleys.

Ok, I'm an idiot. I for some reason thought the thinning post was by @ethompson not @milangravier. Very good points in any case. And I guess my post above is really about small scale irregularities in the grind. I wasn’t thinking as much about large scale irregularities, and I probably should have been.
 
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Jokes aside, polishing is fun, and I value aesthetics a lot. Whatever you want to call it, I'm all for it. As long as the end result is a good cutting knife, it doesn't have to be the "best" cutter. This is KKF, no one here uses their knives enough anyway.

Personally, when I see a knife on BST and the description is stone bevel ready, I put it in the same category as thinning. You've altered the knife if even a little bit, and its no longer the original maker's work alone. Which is fine. That's supposed to happen organically anyway over time, but again, this is KKF.

For instance, I can appreciate the work and skill needed to create this not only beautiful polish, but uniform convexity. I'd be happy to purchase this. But it personally feels like I'm buying a "maker x ethompson" knife, not just the original maker. In the same way some of you send knives to Forty for thinning. When those knives hit BST, you disclose his work.

That's just my 2 cents. Flattening, evening, whatever you call it, the knife is being modified.
I agree on this to a point. I think there's a large difference between someone taking the time to remove material from the bevel following the geometry that the maker established, compared to that same knife having the maker's geometry altered with powered sanding belts into a high wide bevel grind, even if the 1mm/5mm/10mm BTE caliper measurements are the same. I know there's a good number of people to whom these details matter very little, but I find them both very interesting and very important.
 
I agree on this to a point. I think there's a large difference between someone taking the time to remove material from the bevel following the geometry that the maker established, compared to that same knife having the maker's geometry altered with powered sanding belts into a high wide bevel grind, even if the 1mm/5mm/10mm BTE caliper measurements are the same. I know there's a good number of people to whom these details matter very little, but I find them both very interesting and very important.
Yes I can 100% agree on this

I guess I can't fathom being able to even out a knife and follow the exact geometry of the original grind, but if you're skilled enough to do this then I would change my opinion on altering a knife and perhaps just view it as a straight upgrade. I wonder if this is even possible if what’s causing unevenness is a small low spot 🤷🏻‍♂️. Perhaps a different discussion.

But I always thought polishing starts with some form of flattening first, and then re-shaping.
 
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I guess I can't fathom being able to even out a knife and follow the exact geometry of the original grind, but if you're skilled enough to do this then I would change my opinion on altering a knife and perhaps just view it as a straight upgrade. I wonder if this is even possible if what’s causing unevenness is a small low spot 🤷🏻‍♂️. Perhaps a different discussion.
I mean, I wouldn’t call it easy but it’s definitely doable. For that Toyonabe, I lost about 0.75 mm of height and the shinogi moved about the same but the shape and intent behind the bevel and grind was the same. Weighty convex into an extremely thin edge. Personally I don’t think I altered the grind, just smoothed out all the expected wabi sabi. Unless the bevels are fully hollow you don’t have to remove that much metal to get there, you just have to be mindful of where you work and have a clear destination in mind.

Once it’s setup it’s setup for life barring serious damage. Can just throw the bevel on the stones and as long as you work from heel to tip evenly the geometry will be predictable and consistent for the life of the knife.

Which I guess brings me back to my original “unpopular opinion” there is a right and wrong way to do this type of work (in my opinion) - and the term common use of the term flattening probably leads people to jump into doing it the wrong (again my, apparently unpopular, opinion) way.
 
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Yes I can 100% agree on this

I guess I can't fathom being able to even out a knife and follow the exact geometry of the original grind, but if you're skilled enough to do this then I would change my opinion on altering a knife and perhaps just view it as a straight upgrade. I wonder if this is even possible if what’s causing unevenness is a small low spot 🤷🏻‍♂️. Perhaps a different discussion.

But I always thought polishing starts with some form of flattening first, and then re-shaping.
It depends on the geometry and consistency of the grind, IME. It takes a long time, too much time, to get all aspects (e.g. precise "shinogi"/transition at the top of the grind, consistency of the bevel sections top to bottom and front to back (geometrically and scratch pattern wise), etc.) to all be 100%. There's a small group of people doing this kind of work, as a personal pursuit, and almost no one providing it as a service for other people's knives because it's difficult, and time consuming, and often requires task/section specific gear. Essentially it's not at all profitable to do, and most people (rightly) don't care about it since you get really great performance on a large wheel ground concave knife that's decently thin behind the edge, more or less regardless of how inconsistent that concave grind is. That's just one example, but I hope it makes sense that it's faster and far less time consuming to not do it.
 
It takes a long time, too much time, to get all aspects (e.g. precise "shinogi"/transition at the top of the grind, consistency of the bevel sections top to bottom and front to back (geometrically and scratch pattern wise), etc.) to all be 100%. There's a small group of people doing this kind of work, as a personal pursuit, and almost no one providing it as a service for other people's knives because it's difficult, and time consuming, and often requires task/section specific gear.
Raise your hand if you feel personally attacked by @deltaplex

Kidding… you’re absolute my right there is only a small subset of us delusional crazies who care to do this type of thing and see the value in it.

It takes a long time to do and no one bothers to offer this kind of service broadly because to make even a modest living doing this type of stone work you’d have to charge a hilarious amount most would scoff at.
 
I mean, I wouldn’t call it easy but it’s definitely doable. For that Toyonabe, I lost about 0.75 mm of height and the shinogi moved about the same but the shape and intent behind the bevel and grind was the same. Weighty convex into an extremely thin edge. Personally I don’t think I altered the grind, just smoothed out all the expected wabi sabi. Unless the bevels are fully hollow you don’t have to remove that much metal to get there, you just have to be mindful of where you work and have a clear destination in mind.

Once it’s setup it’s setup for life barring serious damage. Can just throw the bevel on the stones and as long as you work from heel to tip evenly the geometry will be predictable and consistent for the life of the knife.

Which I guess brings me back to my original “unpopular opinion” there is a right and wrong way to do this type of work (in my opinion) - and the term common use of the term flattening probably leads people to jump into doing it the wrong (again my, apparently unpopular, opinion) way.
This is fair. I can appreciate honoring the intent. Not trying to single you out, you do fine work. I have an opinion on what constitutes as modification that was addressed by you and @deltaplex that I can respect. And the idea of modifying diverged from the original topic anyway. I wouldn’t call your original opinion unpopular though.
 
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