I don't think the back bevel thickness theory explains this sharpness and toughness standing together. I assume its physical shape itself makes toughness.
holy shit boys! I can't believe I found a 5 year old hidden DBK comment :D now I know why you love convex so much! this mathematical sensei convinced me too! oh man... I'm loving this discovery xD
6 years later, here are my two cents. From a material mechanics perspective (I'm a student of mechanical engineering so please correct me), I think thesituation deals with stress concentrations. The more accute of an angle some object has, that specific point is where the majority of forces will act on a certain area. Depending on the material's properties it has a maximum stress before failure , so that could explain why some steels chip rather than rollling. The round shape could improve in terms of drag while cutting (airplane example). If we only consider your free body diagram of the edge, forces from both sides are equal and in opposite directions, so they would cancel each other. However it is correct to assume that perpendicular forces are the main concern. Great video, makes one think about how complicated designs are. Cheers from Mexico
I had to watch this a few times to understand. When you drew the arrows, I finally realized it. Of course! Convex is stronger for the same reason that an eggshell is very strong! The arc is strong because it directs the force in a different manner, whereas a straight angle has nowhere to direct the force, it must absorb it! Sorry for my long comment, I'm excited I finally understand. Thank you for making this!!! ✌🏻
This video is very important! Most everything can be explained through math and science, yet, in many schools it isn't taught in a manner that is easily digestible as something that can be applied to everyday life. Angles are weak. Period. Any martial artist, architect, or physicist will say just that. You took the time to put it in terms and drawings that are easily grasped, and tested, as we humans love to do. Because this video is a bit older, I would love to see it revisited, and perhaps we can get some other "knife people" on board by tagging them. Start with our Dutch friends Maarten and Mikkie. I am sure they would be willing to participate, discuss, test, and prove the science of edge geometry, and get the material onto more screens. Knowledge gained and shared for the masses. What say you, sir?
Now I get what you mean. Turns out, I've been doing that to my scandi edges all this time. I suppose I should start calling them using your term - scandi-vex. This may also be the reason for the initial brittleness/weakness of all my factory edges. First I thought it was something to do with overheated bevels, which were being removed after first few hones. Now I think it's rather my honing 'convexing' the brittle scandi grind thus making it tougher. It may seem like not much of a difference, but in reality, edge holding and chip/roll-resistance is considerable and noticeable.
I believe this is called a micro bevel, a tiny higher angle bevel on the actual bevel. This will give it a convex geometry which will look more like a triangle than an oval.
@@ichich3276 It would be if we kept a more-or-less consistent angle, limited to a couple of millimeters in height. What he did there, and what I believe I've been doing, is avoid maintaining one specific angle and round a large portion of the edge all the way up to the top of the grind, or in this case, even higher.
Yes The best advantage of the convex over the flat grind is at the most acute angle where it leaves enough metal behind the edge to maintain edge support integrity. It is the sweet spot. Using a resilient material of no less than 55 durometer, supporting sandpaper and the blade at approx 15 degrees and 500gms downward pressure. Less pressure produces a more acute sharper angle but then it becomes more of a straighter edge with less metal behind for support and increase associated risk of chipping and rolling over.
Sane reason why so many ancient structures used convex arches...tabernacles and cathedrals you see them everywhere. The force pusing down on "the point" is redirected, a modified arch.
Thank you for the theory Wako, It's very logical and I've experienced that my convexed knives work better and are a bit more resilient that my standard V edges as well. A good thing is that slowly convexing the knife by stropping will thoughen the knife in time. Have a nice day.
One element that is tough to measure empirically, but that I believe makes a difference in a blade's ability to slice, particularly through meat, is the value of the highly polished secondary edge. During the convex edge creation/sharpening process, the area just above the primary edge ends up highly polished. I don't think this element is has more of an effect than the geometry or physics of the blade, but I do think it contributes to the ease by which a blade moves through material. Could the convex's edges be getting more credit than they deserve here? I don't have a definitive answer, but its a good question.
This makes sense, never thought of it like this. This hypothesis would also be partially supported by the science of sabres and other curved swords in fencing and hema research, the curvature of the blade increases the cutting potential as there is a smaller energy transfer point with a curved blade vs a straight edged blade, even though this is on a much smaller scale the mechanics should be the exact same.
I believe the convex geometry allows the cutting material to push away from the incision, so it allows it to "flow" away from the edge better. Where V edge allows the material to remain constant against the edge.
Thx for the great videos, all of them. I bought my first bark river knife for 2 moths ago, a bravo 1, what a great knife. But as you said in a nother video it has a secondary edge from factory. So I looked at youre videos how to remove it and give the knife full convex edge and WOW !! I can understand why you like bark river knives. If i buy more knives it will absolutly be from bark river. Thx for the great videos and instructions how to sharpen a knife
Very interesting idea, I have always been a fan of convex edges, I feel they are the most superior, but I never took the time to drawl a force diagram. It makes sense but I have a few doubts: The "V" bevel contains the convex bevel. So that means all the forces you drew on the convex bevel also apply internally to the V bevel. The only difference would be a slight change in direction in the force. In this case the V bevel is more prone to sending the force perpendicular to the plane, into the blade on the grind. The Convex edge like your diagram shows, sends the force in an array, but since it becomes closer to 90 degrees faster, it is sending the force closer to the bevel where the grind is thinner. Also keep in mind that steel is not a perfect fluid constancy, it is grainy, so even modern small grain steel is going to naturally spread shook in a non linear way.
weethetbeter You seem to be mistaken. A convex edge is not rounded at the very edge. A 30 degree convex edge comes to a crown that is identical to a 30 degree "V" bevel edge. A zero grind (flat from the edge to spine) is the sharpest, but has almost no strength. An out door blade even made of CPM 3V with a zero grind would not survive.
For me is the sharpest grind scandi (without bevel). Very sharp, bevel always makes resistance in cut. But I have knives with flat grind and very small bevel too. I have never had any problem with strength of the steel but I'm using knife mostly for cutting, not for batoning or chopping. For these works I have an axe or parang. Best regards.
Interesting theory, but I believe the effects are more minimal than you think because steel is not a particularly compressible material. I think more of the reason the physics you explained about the angle makes convex tougher is that it leads to a more spread out stress dissipation across the edge. I think it is a combination of some of that in addition to the fact that regrinding a v-edge to a convex makes it thinner overall and requires less overall force, and the fact that sharp curves in a material make high pressure zones when it is stressed that can lead to fracturing. The last reason is why no mechanical parts on race cars have champers or sharp edges, everything is rounded for the primary reason of making it stronger, especially against quick impulse.
You have to remember that a really sharp edge will split whatever you are cutting though, so the forces will not hit from the front directly. A convex shape is still tougher while maintaining a thin edge, a fair trade :) I think for the physics-part, having very little friction on the edge (i.e. mirror polish) is one of the most important things if you apply your physics, but I think the thickness of the edge is more important than the direction of forces. Nonetheless, I prefer a single, convex edge too :)
I think i has more to do with how the edge bends ... because even straight push-cutting is never perfectly centered especially when applying a lot of force... in flat secondary bevel grind strain is localized on the secondary bevel and the sharp transition doesn't allow it to be relieved smoothly along the edge length and width ... you can observe this is if you try to bend the edge on hard surface with small curvature (for example a lighter) ... GOOD THINK IS CONVEXING HAPPENS SORT OF NATURALLY when you are manually sharpening so after sharpening even flat edge is slightly convex you just need to exagerate it a bit to remove the trasition and make the edge continuous ... FOR ME THE GREATEST ADVANTAGE IS THAT CONVEX EDGES RETAIN THEIR GEOMETRY AFTER A LOT OF RESHARPENING ... with flat edges you need to remove material from both the primary and secondary edge when width changes which is harder ... NICE EXPLANATION! THANK YOU
I think that when you are convexing a V-edge, the apex of the edge does not stay constant. I think it lowers itself through the convexing process, or at least I assume it does when I do it to my blades. I am removing material beyond the shoulder towards the edge, and I actually hit the edge removing some material from there, attacking it from both sides, thereby making the edge angle fatter.
jajebiewpizdujebana You just have to watch the videos. I will look and see if I can find what is what, at least the titles if not the links, it is a series of 3 videos and then 1 seperate video where he focuses on why he makes his edges the way he does, it isn't listed in the title of the video.
hello virtuovice, I've just started watching your videos and you're just amazing at what you do and also fun to learn from. I have just started doing my own knife sharpening and I just want to know how you actually get a convex grind on a blade. like holding angle and technique and everything in between. you can pm me if you would like. thanks
Enjoyed the video. The math necessary to prove your theory is beyond my capability. Never the less, I'd be convexing my conventional grinds without these insights as my usage tells me that they work better. Empirical evidence is my truth. Your analogy to airplane design reminded me of something I read once. Early in the development of air frame structures an attempt to use square windows proved to be a failure. They cracked and broke causing obvious issues to the aircraft. When round or oval shaped windows were substituted the problem was eliminated. While this, as one of your commentators pointed out, is not perfectly analogous to a knife edge discussion, it is interesting that different geometric shapes do in fact react to the same stresses with different outcomes. Its not always intuitive.
hi sir, thanks for a very informative video, i wanted to know how many game do you usually dress before a good knife according to your standards is again required to sharpen? thanks again...
Now I always carry two hunting knives, one in A2 or 3V and the other in Elmax as a backup. Up to 2 deer I don't need to use Elmax when the primary knife is in A2. 3V does more. If I don't need to, I don't like to use Elmax since it has a very little chippy character while it always gives me the sharpest edge for the longest time. I always strop every used knife after coming home. And in almost all cases stropping is enough to make the edge the sharpest again. Thanks.
I dont agree. Geometrically convex offers a smoother transition thus the candidate for a n even (smoorh you may say) load transfer. Yet I need to model the knife so as to be sure. One cant simplify the load paths within a knife as such.
I think your theory makes very much sense! thank you for sharing
holy shit boys! I can't believe I found a 5 year old hidden DBK comment :D now I know why you love convex so much! this mathematical sensei convinced me too! oh man... I'm loving this discovery xD
6 years later, here are my two cents. From a material mechanics perspective (I'm a student of mechanical engineering so please correct me), I think thesituation deals with stress concentrations. The more accute of an angle some object has, that specific point is where the majority of forces will act on a certain area. Depending on the material's properties it has a maximum stress before failure , so that could explain why some steels chip rather than rollling. The round shape could improve in terms of drag while cutting (airplane example). If we only consider your free body diagram of the edge, forces from both sides are equal and in opposite directions, so they would cancel each other. However it is correct to assume that perpendicular forces are the main concern. Great video, makes one think about how complicated designs are. Cheers from Mexico
Excellent explanation ..
Wish you would do more of these
kinds of knife videos ..
Great engineering explanation ..
We are not worthy. I always look forward to your videos sir. You are the Doctor of the bladed edge. Thank you for your time and passion.
I had to watch this a few times to understand. When you drew the arrows, I finally realized it. Of course! Convex is stronger for the same reason that an eggshell is very strong! The arc is strong because it directs the force in a different manner, whereas a straight angle has nowhere to direct the force, it must absorb it! Sorry for my long comment, I'm excited I finally understand. Thank you for making this!!! ✌🏻
This video is very important! Most everything can be explained through math and science, yet, in many schools it isn't taught in a manner that is easily digestible as something that can be applied to everyday life. Angles are weak. Period. Any martial artist, architect, or physicist will say just that. You took the time to put it in terms and drawings that are easily grasped, and tested, as we humans love to do. Because this video is a bit older, I would love to see it revisited, and perhaps we can get some other "knife people" on board by tagging them. Start with our Dutch friends Maarten and Mikkie. I am sure they would be willing to participate, discuss, test, and prove the science of edge geometry, and get the material onto more screens. Knowledge gained and shared for the masses. What say you, sir?
Now I get what you mean. Turns out, I've been doing that to my scandi edges all this time. I suppose I should start calling them using your term - scandi-vex. This may also be the reason for the initial brittleness/weakness of all my factory edges. First I thought it was something to do with overheated bevels, which were being removed after first few hones. Now I think it's rather my honing 'convexing' the brittle scandi grind thus making it tougher. It may seem like not much of a difference, but in reality, edge holding and chip/roll-resistance is considerable and noticeable.
I believe this is called a micro bevel, a tiny higher angle bevel on the actual bevel. This will give it a convex geometry which will look more like a triangle than an oval.
@@ichich3276 It would be if we kept a more-or-less consistent angle, limited to a couple of millimeters in height. What he did there, and what I believe I've been doing, is avoid maintaining one specific angle and round a large portion of the edge all the way up to the top of the grind, or in this case, even higher.
Yes The best advantage of the convex over the flat grind is at the most acute angle where it leaves enough metal behind the edge to maintain edge support integrity. It is the sweet spot. Using a resilient material of no less than 55 durometer, supporting sandpaper and the blade at approx 15 degrees and 500gms downward pressure. Less pressure produces a more acute sharper angle but then it becomes more of a straighter edge with less metal behind for support and increase associated risk of chipping and rolling over.
Sane reason why so many ancient structures used convex arches...tabernacles and cathedrals you see them everywhere. The force pusing down on "the point" is redirected, a modified arch.
I love how scientifically you explained your thoughts and experience. Thank you for sharing.
Thank you for the theory Wako, It's very logical and I've experienced that my convexed knives work better and are a bit more resilient that my standard V edges as well. A good thing is that slowly convexing the knife by stropping will thoughen the knife in time. Have a nice day.
I'm amazed! Thank you for this important information, you have changed my mind about sharpening. Great videos! Do you ever go for wild boar hunting?
Georg We have no wild boars on this north island Hokkaido Japan.
One element that is tough to measure empirically, but that I believe makes a difference in a blade's ability to slice, particularly through meat, is the value of the highly polished secondary edge. During the convex edge creation/sharpening process, the area just above the primary edge ends up highly polished. I don't think this element is has more of an effect than the geometry or physics of the blade, but I do think it contributes to the ease by which a blade moves through material. Could the convex's edges be getting more credit than they deserve here? I don't have a definitive answer, but its a good question.
This makes sense, never thought of it like this.
This hypothesis would also be partially supported by the science of sabres and other curved swords in fencing and hema research, the curvature of the blade increases the cutting potential as there is a smaller energy transfer point with a curved blade vs a straight edged blade, even though this is on a much smaller scale the mechanics should be the exact same.
I believe the convex geometry allows the cutting material to push away from the incision, so it allows it to "flow" away from the edge better. Where V edge allows the material to remain constant against the edge.
Thx for the great videos, all of them. I bought my first bark river knife for 2 moths ago, a bravo 1, what a great knife. But as you said in a nother video it has a secondary edge from factory. So I looked at youre videos how to remove it and give the knife full convex edge and WOW !! I can understand why you like bark river knives. If i buy more knives it will absolutly be from bark river. Thx for the great videos and instructions how to sharpen a knife
I agree!
The shoulders do nothing but increase drag and decrease cutting. They don't even increase edge strength.
Fascinating theory. Makes a lot of sense. Thanks!
This is the most interesting video I've seen in quite some time. Thanks for the information.
Very interesting idea, I have always been a fan of convex edges, I feel they are the most superior, but I never took the time to drawl a force diagram. It makes sense but I have a few doubts:
The "V" bevel contains the convex bevel. So that means all the forces you drew on the convex bevel also apply internally to the V bevel. The only difference would be a slight change in direction in the force. In this case the V bevel is more prone to sending the force perpendicular to the plane, into the blade on the grind. The Convex edge like your diagram shows, sends the force in an array, but since it becomes closer to 90 degrees faster, it is sending the force closer to the bevel where the grind is thinner.
Also keep in mind that steel is not a perfect fluid constancy, it is grainy, so even modern small grain steel is going to naturally spread shook in a non linear way.
Thank you!
weethetbeter You seem to be mistaken. A convex edge is not rounded at the very edge. A 30 degree convex edge comes to a crown that is identical to a 30 degree "V" bevel edge.
A zero grind (flat from the edge to spine) is the sharpest, but has almost no strength. An out door blade even made of CPM 3V with a zero grind would not survive.
Dan Martin thanks Dan, that's i am trying to say. If a cutting edge would be round to the tip there is no edge.
For me is the sharpest grind scandi (without bevel). Very sharp, bevel always makes resistance in cut. But I have knives with flat grind and very small bevel too. I have never had any problem with strength of the steel but I'm using knife mostly for cutting, not for batoning or chopping. For these works I have an axe or parang. Best regards.
Interesting theory, but I believe the effects are more minimal than you think because steel is not a particularly compressible material. I think more of the reason the physics you explained about the angle makes convex tougher is that it leads to a more spread out stress dissipation across the edge. I think it is a combination of some of that in addition to the fact that regrinding a v-edge to a convex makes it thinner overall and requires less overall force, and the fact that sharp curves in a material make high pressure zones when it is stressed that can lead to fracturing.
The last reason is why no mechanical parts on race cars have champers or sharp edges, everything is rounded for the primary reason of making it stronger, especially against quick impulse.
Love your videos!!!
You have to remember that a really sharp edge will split whatever you are cutting though, so the forces will not hit from the front directly. A convex shape is still tougher while maintaining a thin edge, a fair trade :) I think for the physics-part, having very little friction on the edge (i.e. mirror polish) is one of the most important things if you apply your physics, but I think the thickness of the edge is more important than the direction of forces. Nonetheless, I prefer a single, convex edge too :)
I think that you are right.... I believe that I know that you are right.
I've honestly never thought of it that way. Very insightful.
I think i has more to do with how the edge bends ... because even straight push-cutting is never perfectly centered especially when applying a lot of force... in flat secondary bevel grind strain is localized on the secondary bevel and the sharp transition doesn't allow it to be relieved smoothly along the edge length and width ... you can observe this is if you try to bend the edge on hard surface with small curvature (for example a lighter) ... GOOD THINK IS CONVEXING HAPPENS SORT OF NATURALLY when you are manually sharpening so after sharpening even flat edge is slightly convex you just need to exagerate it a bit to remove the trasition and make the edge continuous ... FOR ME THE GREATEST ADVANTAGE IS THAT CONVEX EDGES RETAIN THEIR GEOMETRY AFTER A LOT OF RESHARPENING ... with flat edges you need to remove material from both the primary and secondary edge when width changes which is harder ... NICE EXPLANATION! THANK YOU
Thank you. This was very inspiring and helpful.
I think that when you are convexing a V-edge, the apex of the edge does not stay constant. I think it lowers itself through the convexing process, or at least I assume it does when I do it to my blades. I am removing material beyond the shoulder towards the edge, and I actually hit the edge removing some material from there, attacking it from both sides, thereby making the edge angle fatter.
You are right. The apex angle can be even larger than anticipated. Thanks.
Very informative and interesting concept, as always a top video,thanks for sharing with us as we use hunting knives every day.
Thanks again my friend.
Very well thought out my friend.
You are brilliant. I wonder if you would like a knife made just as you specify? (Size, shape, steel, and handle, all of it)
Good explanation, thank you very much!
Have you seen Kylie Harris' video on convex edges and grinds? I think you might like his point of view, and his explanation is very well done on CAD.
Link?
yvranx knivesandstuff channel, tho i couldnt find the one where he explains convex
jajebiewpizdujebana You just have to watch the videos. I will look and see if I can find what is what, at least the titles if not the links, it is a series of 3 videos and then 1 seperate video where he focuses on why he makes his edges the way he does, it isn't listed in the title of the video.
hello virtuovice, I've just started watching your videos and you're just amazing at what you do and also fun to learn from. I have just started doing my own knife sharpening and I just want to know how you actually get a convex grind on a blade. like holding angle and technique and everything in between. you can pm me if you would like. thanks
Its a good thing i cant keep an edge flat if i try. The way i sharpen my edges always end up convex
Well it makes sense. Arches have more strength than triangles.
Brilliant 👍👍👍
Could this be the same principle as arches in architecture?
Hope you can do more english videos this year. I watch yourJapanese but fell I lose something in translation. LOL
So the convex edge is stronger and last longer. Correct.
I agree.
interesting. thank you for sharing.
Enjoyed the video. The math necessary to prove your theory is beyond my capability. Never the less, I'd be convexing my conventional grinds without these insights as my usage tells me that they work better. Empirical evidence is my truth.
Your analogy to airplane design reminded me of something I read once. Early in the development of air frame structures an attempt to use square windows proved to be a failure. They cracked and broke causing obvious issues to the aircraft. When round or oval shaped windows were substituted the problem was eliminated. While this, as one of your commentators pointed out, is not perfectly analogous to a knife edge discussion, it is interesting that different geometric shapes do in fact react to the same stresses with different outcomes. Its not always intuitive.
hi sir, thanks for a very informative video, i wanted to know how many game do you usually dress before a good knife according to your standards is again required to sharpen? thanks again...
Now I always carry two hunting knives, one in A2 or 3V and the other in Elmax as a backup. Up to 2 deer I don't need to use Elmax when the primary knife is in A2. 3V does more. If I don't need to, I don't like to use Elmax since it has a very little chippy character while it always gives me the sharpest edge for the longest time.
I always strop every used knife after coming home. And in almost all cases stropping is enough to make the edge the sharpest again. Thanks.
Wow.. What a great video.. :D
Hy-poth-e-sis issue= ish-oo
I dont agree. Geometrically convex offers a smoother transition thus the candidate for a n even (smoorh you may say) load transfer. Yet I need to model the knife so as to be sure. One cant simplify the load paths within a knife as such.
elvis3571
Did you model it yet? I'm interested in your findings.
not true... your vector sketch is completely wrong. you think the wrong way.