Convexity, flatness, stiction and food release

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blokey

blokey

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I recently got into an argument online on food release, the other person insist that the only way to increase the food release without resort to thing like S grind is increase the thickness of the knife, and the slight convexity on the kitchen knife is not intentional but rather a flaw of the manufacturing equipment. His point is the flat V grind is better than convex because it cuts better and the slight convexity on kitchen won't affect stiction and food release, and a microbevel will do more for food release. which really contrary to my own experience. This got me curious, is there any serious study on this subject matter? any physical model we can use to determine if the slight convexity actually does affect food release?
 
M1k3 said:
No serious study that I'm aware of.

That said, 2 flat planes have a higher surface contact patch and therefore higher coefficient of friction/drag. 2 curved planes have a small contact patch and lower coefficient of friction/drag.
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Science hat on. Coefficient of friction is not affected by surface area. It's based on the smooth/roughness of the surface. Friction or drag force is equal to coefficient of friction times the perpendicular force between the two objects.

That being said, I do believe convexity helps with sticking, but I'm not sure the actual mechanics behind it. But I'd say it's not simply "friction" in the technical sense.
 
Slice a cucumber with a flat grind vs a convex knife and you'll discover the advantage - on a convex knife the slices will come off easier.

IMO, the advantage of any grind decreases as the size of the product decreases. Slicing a potato, the grind has an effect, but dicing garlic it has little effect.
 
tostadas said:
Science hat on. Coefficient of friction is not affected by surface area. It's based on the smooth/roughness of the surface. Friction or drag force is equal to coefficient of friction times the perpendicular force between the two objects.

That being said, I do believe convexity helps with sticking, but I'm not sure the actual mechanics behind it. But I'd say it's not simply "friction" in the technical sense.
Click to expand...
Corrected my post
 
Or maybe a better explanation is something having to do with surface tension? I don’t really know any physics, but watery ingredients are the ones that stick the most. If you have a slice of something that’s stuck onto the knife with water in between, it can’t come straight off perpendicularly because the water will create a sort of suction effect, and maybe somehow surface tension or something keeps it from shearing. If the knife is flat ground, it’s easier for this to happen, while if the slices are flat and the knife is convex it’s harder to get the slice stuck on by water in the first place.

Edit: writing this post makes me realize I don’t really know what surface tension is, beyond my own experimentally informed intuition.
 
I've made flatter knives, and more convex ones, and what I found was that food release is better with a thicker knife regardless. My guess is that with a thicker blade, and therefore steeper blade face/cross sectional geometry, the angle of deflection is going to be higher increasing the peeling effect. A wider boat makes a wider wake type idea.
 
Wonder if a thicker knife will also create a less clean cut on some ingredients, resulting in less sticking. Or the fact that it’s pushing the slice forcefully to the side stresses it so that at the end of the cut the slice pops a bit, making it more likely to be flung off. Or is that what you meant by the peeling effect?
 
Maybe the blade finish play role too on food release and stickiness . I tried ashi's AEB-L Gyuto (thin blade, convex edge) and food release is ok. Yanagiba in the other hand if I finish it with 3000 grit rough kasumi finish food will get stuck and create friction, with mirror finish/ polish food just glide thru fish or protein like nothing. Fat content also make a difference and I think most of. People here already know. That come only from my experience and someone maybe experience it differently.
This is a good thread, let's see what other people think about this.

Maybe someone studied about this
 
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ian said:
Wonder if a thicker knife will also create a less clean cut on some ingredients, resulting in less sticking. Or the fact that it’s pushing the slice forcefully to the side stresses it so that at the end of the cut the slice pops a bit, making it more likely to be flung off. Or is that what you meant by the peeling effect?
Click to expand...
Not quite. Think of an acute triangle for a moment, pointing upwards, now picture a vertical line intersecting one of the top two lines, that will represent an object in motion making contact with that triangle. The angle formed between that vertical line and the line forming that side of the triangle, though some trigonometric voodoo that I've forgotten since I took physics will give you the the amount of force being directed downwards and the amount of force being directed outwards. The same thing can apply to something with a curved/ogived outline, a boat, a bullet, you name it. So on a thicker knife the angle of the radius that creates the convex section of the edge will be steeper (assuming the height of the convexity is equal between two blades of different thicknesses), the amount of force directed outward is greater. There's greater deflection pressure to pull the food out and away from the primary bevel angle, which is more acute than that of the convexed area.

But also definitely, thicker knives will break harder foods like carrots. Those will pop off and fly for a ways.
 
ian said:
Wonder if a thicker knife will also create a less clean cut on some ingredients, resulting in less sticking. Or the fact that it’s pushing the slice forcefully to the side stresses it so that at the end of the cut the slice pops a bit, making it more likely to be flung off. Or is that what you meant by the peeling effect?
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Remember them fat knives that start splitting the ingredient before the edge even gets there?
 

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refcast said:
Scientific articles must be paid for . . . Or the authors asked for a free reading sample I guess. Or maybe sci hub

Oh here's one. . . Still doesn't answer food release though, only cutting force. The math is mathy . . . But seems to be calculus and not something more obscure

http://dspace.nuft.edu.ua/handle/123456789/21119
Click to expand...

Damn that article is hard to understand…. I get that English isn’t their first language, but man. I’m not completely convinced it’s not AI generated.
 
blokey said:
I recently got into an argument online on food release, the other person insist that the only way to increase the food release without resort to thing like S grind is increase the thickness of the knife, and the slight convexity on the kitchen knife is not intentional but rather a flaw of the manufacturing equipment. His point is the flat V grind is better than convex because it cuts better and the slight convexity on kitchen won't affect stiction and food release, and a microbevel will do more for food release. which really contrary to my own experience. This got me curious, is there any serious study on this subject matter? any physical model we can use to determine if the slight convexity actually does affect food release?
Click to expand...
What is his arguement to support that "thickness helps with food release"?


That's absurd

Edit: by thickness, what does he mean exactly spine? Directly behind the edge? Halfway up the knife? In any regard. Convexity will definitely help. Exactly where the convexity starts and stops I suspect plays a big role, and likely isn't considered enough.

Maybe someone should do a test, and check convexing the primary bevels of a few knives in different areas, and to different degrees and see where the difference can be found.
 
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jwthaparc said:
What is his arguement to support that "thickness helps with food release"?


That's absurd

Edit: by thickness, what does he mean exactly spine? Directly behind the edge? Halfway up the knife? In any regard. Convexity will definitely help. Exactly where the convexity starts and stops I suspect plays a big role, and likely isn't considered enough.

Maybe someone should do a test, and check convexing the primary bevels of a few knives in different areas, and to different degrees and see where the difference can be found.
Click to expand...
I think he means by spine, which is not technically wrong but also weird considering convexity use some of the same principle but more smooth cutting experience. (at least according to my personal experience)
 
Blade polish has a significant impact. Polish a knife towards a mirrorish finnish and it'll start sticking like hell.
 
I've put a lot of thought into this subject over the last 5 years, but my god... it's difficult to explain in words. Arguments go into crazy circles that tend to go nowhere fast. I try not to get into it these days, hoping that my old threads here on this forum will explain most of it.

The following quote is interesting though:
blokey said:
...the slight convexity on the kitchen knife is not intentional but rather a flaw of the manufacturing equipment...
Click to expand...
Has anyone here got a Victorinox Fibrox/Classic Chef's Knife to check the grind? I believe they are an example of a flat grind on a mass manufactured knife. I might be wrong though...
 
Kippington said:
I've put a lot of thought into this subject over the last 5 years, but my god... it's difficult to explain in words. Arguments go into crazy circles that tend to go nowhere fast. I try not to get into it these days, hoping that my old threads here on this forum will explain most of it.

The following quote is interesting though:

Has anyone here got a Victorinox Fibrox/Classic Chef's Knife to check the grind? I believe they are an example of a flat grind on a mass manufactured knife. I might be wrong though...
Click to expand...
Hmm I wasn't even considering the entirely mass produced kitchen knives into this conversation. It could be a "manufacturing defect" but I feel like more than likely if they really wanted a truly flat grind, they could easily pull it off.
 
Kippington said:
A1
Has anyone here got a Victorinox Fibrox/Classic Chef's Knife to check the grind? I believe they are an example of a flat grind on a mass manufactured knife. I might be wrong though...
Click to expand...
Many mass produced knives are fully flat including victorinox as far as I can remember when I had one a while back. Spyderco Carter are as well at least the first release of AS core. There is no problem creating full flat grinds.

I think when they say that to increase food release you need a thicker knife I think they mean that you can do a lot more with geometry with a thick stock. You can do extreme convex, concave, wide bevels versions, etc. On a thin stock knife there isn't much you can do.

I think we here care too much about food release because we are heavily influenced by pro cooks doing tons of prep. In that scenario good food release can be very helpful.

The outdoor, folder guys who start looking into kitchen knives don't understand food release at all on the other hand. They also don't understand thinning in general. Due to this they tend to think that really thin full flat chef knives are the best. The reason is that they go through food the best and are the easiest to keep sharp and to have the same grind for the life of the knife. Convex grinds cause all sorts of problems for them. They are also used to mostly cutting dry hard stuff so they don't understand that cutting food in volume and fast is different.

Empirically full flat grind is not the best for a chef knife and food release matters. Very thin blades on chef knives are also not the best. A lot depends on preference, technique and the ingredients being cut most of the time.
 
Jovidah said:
From what I've seen online most people into outdoor and folder knives seem more obsessed with polishing their bevels into a mirror shine than how it actually cuts. :p
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There is that too of course, but many do know what they are talking about and many think people here don't understand that thinner knives just cut better.

A lot of it has to do with what the two groups cut and how, but also with the size of the knives and just the amount of steel we are dealing with in chef knives. Something that is best in a 4" narrow blade that has to cut wood well might not be that great in a 10" gyuto that mostly cuts all sorts of veggies.
 
I can say there used to be a big disconnect between the pocket knife community, blade stock thickness, and thickness behind the edge. You can still go to pocket knife reviews, and most just worry about how thick the spine is, and ignore the behind the edge thinness.

There has been a movement towards importance of behind the edge thickness taking priority more lately. Before this it seemed there was an idea that just because a knife had thin blade stock that it would slice well. Discounting that something that is thicker at the spine, but thinner behind the edge could potentially cut much better.
 
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I would go even further and say at some not so distant past the focus of folders/fixies was into thick stocks, the thicker the marrier. I am glad to see that in few past years this trend have changed.
 
Ruso said:
I would go even further and say at some not so distant past the focus of folders/fixies was into thick stocks, the thicker the marrier. I am glad to see that in few past years this trend have changed.
Click to expand...
I agree even though I feel it is not changing enough. Still a bunch of thick blades on small knives and folders as well. Even when tougher steels are used still blades are very thick on many. The reason is usually to make the knife tougher, but folders weak point is usually the handle to blade attachment and not the blade itself. It is getting better though just slowly.
 
https://www.kitchenknifeforums.com/threads/like-a-naughty-schoolboy.44589/page-4#post-856223
My totally real life but unscientific potato slap down test suggests that a flat grind performs better when it comes to potato stiction. Check out my two top performers. My high flat grind Rader, and another high flat grind Gyuto by Alex Horn. Rader thick, Horn thin. Two top performers. The primary conclusion … expensive, rare flat knives out perform less rare cheaper blades. Tall and thin are preferred to taller and slightly more shapely.

Rader

41CEDE40-2B97-4E71-B694-5D50EBD48468.jpeg


Horn

73B1A02B-C938-4855-9AE9-97694E8379C1.jpeg
 
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Brian Weekley said:
https://www.kitchenknifeforums.com/threads/like-a-naughty-schoolboy.44589/page-4#post-856223
My totally real life but unscientific potato slap down test suggests that a flat grind performs better when it comes to potato stiction. Check out my two top performers. My high flat grind Rader, and another high flat grind Gyuto by Alex Horn. Rader thick, Horn thin. Two top performers. The primary conclusion … expensive, rare flat knives out perform less rare cheaper blades. Tall and thin are preferred to taller and slightly more shapely.

Rader

View attachment 187212

Horn

View attachment 187213
Click to expand...

That Radar looks hollow ground to me - what happens if you put a ruler against it?
 
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