What Are The Advantages of a Convex Grind?

marcinek said:
I'll be waiting for that. Draw 2 angles that are the same. Draw the v grind in one and the convex in the other.
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herisson said:
You're just proving you're confusing sharpening angle and apex angle. They will be the same if you work your blade with a steady angle on a flat stone : hold the blade at 17°, you'll get a 17° V bevel, all 17° up to the apex. Now, take the same blade to a belt sharpener, set the angle of the tool at 17° and proceed. Now measure the angle at the apex and I can tell you it will be more than 17°. By the way, your artistic picture shows it quite well : the convexed blade on the left has been sharpened at a way steeper angle than the V to acheive a more or less similar "apex angle". Geometry is real world stuff.
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marcinek said:
The geometries are not equal but the edge angles are. You are simply misunderstanding mathematics. And, as much as would might want to ignore it, the real world behaves according to the laws of mathematics and geometry.

I'm sorry neither support your argument.
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FortyTwoBlades said:
Actually he's right, and I don't think you're understanding what he's showing. Convexes will have a continuously decreasing angle the further back you get from the edge but at the apex will be identical in angle. The closer to the edge you get the greater the order of magnitude of influence specific geometry has on cutting performance. For equal edge angle, a convex will have superior cutting performance, but less lateral support to resist torque/side-loads. A 50° V edge would have to be compared to a convex with a 50° apex, but of the two the convex would overall be thinner. Convexes, not being limited to a linear geometry, can have more variation in them, though, and so some may be done thinner or thicker while retaining that same edge angle at the apex. When people convex their knives and make them tougher it's because they're not properly accounting for the deflection of their abrasive surface and so are inadvertently just thickening their edge angle. You could do a similar thing by just thickening the apex of a V grind. A straight V grind will thicken continuously, the angle is staying constant. That's kind of what makes it a V instead of a convex or hollow. :)
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SpySmasher said:
Mick, Marcinek is right. When comparing a V grind to a convex grind of equal edge angles, the V grind will have more metal behind the edge. The convex grind starts at that angle but quickly gets thinner while the V grind retains it's angle.
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My goodness. Some people just cannot understand the concept. You can cling to your mathematical equation all you like, because you are only seeing HALF the picture. YES the angle and the apex IF FOLLOWED forever on a straight line will be thicker behind the edge on the V grind. BUT - whos knife edge bevel continues forever and ever in a straight line??? In real life, when we are talking knives and ACTUAL USE when it comes to cutting geometry, the convex edge allows more metal behind the edge over a short distance because of the difference between the start of the cutting edge angle and and the angle it actually is when you connect the two points with a straight line. Here's a picture i drew for you so you can grasp what we are trying to say regardless of your mathematical point. In a mathematical sense if you measure forever in a straight line, the V grind wins. IF you measure a REAL KNIFE IN REAL LIFE - the convex wins for metal behind the edge between the shoulder and the cutting edge. End of story. Now you can argue the V edge will have more metal if you continue the apex angle in a straight line forever and ever, but the fact is that is a moot point when put into real word cutting geometry/performance examples. Nobodys knife continues in a straight like forever, you are clinging to that mathematical fact to side step the real word use point i'm trying to make.

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SpySmasher said:
The red line is the edge angle, not the green line.
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Yeah well spotted genius, keep trying to side step the point about cutting geometry by arguing technical terms. I know what im talking about and you know we all understand the concept. Your imaginary V grind that spans for hundreds of meters is a non existent concept. Do you even realise there is no micro bevel for the apex on a convex? so there are different parts of the convex that basically cover, the primary edge angle and the apex all in one.
 
Mick_1KRR said:
Yeah well spotted genius, keep trying to side step the point about cutting geometry by arguing technical terms. I know what im talking about and you know we all understand the concept. Your imaginary V grind that spans for hundreds of meters is a non existent concept.
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Don't know why you are so steamed. We are talking about technical issues, using the correct terminology is important to understanding.
 
marcinek said:
Unfortunately the "tangent" concept escapes people.

Maybe I should try BOLD UPPERCASE LETTERS!
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You should try looking at the pretty pictures and stop trying to escape reality when it comes to edges. It's ok to be wrong. You're still correct about your imaginary V grind that spans for 3 meters long to win at having more metal behind the edge. Unfortunately, you're wrong when it comes to a real knife in the real world when the shoulder and the apex are both intersecting in a straight line in regards to the overall angle.
 
SpySmasher said:
Don't know why you are so steamed. We are talking about technical issues, using the correct terminology is important to understanding.
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No quite, you're arguing terminology with a complete disregard to a picture that proves the convex has more metal behind the edge when looking at a short distance between a shoulder and apex. But hey, i understand that everyone wants to be correct, but we're talking knives, not imaginary scenarios where the edge will span for miles and miles thus making a V grind contain more metal behind the edge. I don't understand how people can't understand the concept.
 
I use a convex grind on my choppers a machetes. If they have a flat grind I use a convex edge. I have noticed a big advantage over a V grind/edge. A lot less dings, edge rolls, and other edge deformations. Some of my folders have a convex grind and edge, but they are quite thin behind the edge and cut very well. I like both, just for different tasks.
 
Mick_1KRR said:
You should try looking at the pretty pictures and stop trying to escape reality when it comes to edges. It's ok to be wrong. You're still correct about your imaginary V grind that spans for 3 meters long to win at having more metal behind the edge. Unfortunately, you're wrong when it comes to a real knife in the real world when the shoulder and the apex are both intersecting in a straight line in regards to the overall angle.
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o_O Not at all sure what you are talking about with the imaginary 3 m v grind, but you are more than welcome to pretend the tangent concept doesn't exist. That kinda makes calculus go away, and the planets to fling off into deep space and stuff, but its cool. :thumbsup:
 
Mick_1KRR said:
You should try looking at the pretty pictures and stop trying to escape reality when it comes to edges. It's ok to be wrong. You're still correct about your imaginary V grind that spans for 3 meters long to win at having more metal behind the edge. Unfortunately, you're wrong when it comes to a real knife in the real world when the shoulder and the apex are both intersecting in a straight line in regards to the overall angle.
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Except you have been arguing with people who have made statements about the grinds having the same edge angle. They made a claim, which was correct, you told them they were wrong, which was incorrect, and in response drew a diagram proving their point. You are right that in the knife you describe the convex edge has more metal behind the edge but that is not the conversation you jumped in to "correct." Also, you got mad at me for explaining why they were right.

And you will probably get even madder since I've recounted this series of events.
 
SpySmasher said:
Except you have been arguing with people who have made statements about the grinds having the same edge angle. They made a claim, which was correct, you told them they were wrong, which was incorrect, and in response drew a diagram proving their point. You are right that in the knife you describe the convex edge has more metal behind the edge but that is not the conversation you jumped in to "correct." And then got mad at me for explaining why they were right.

And you will probably get even madder since I've recounted this series of events.
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I could not be more calm, im just honestly confused that people are trying to side step the point i was trying to make. You even just said yourself that i am correct with the example i'm making, it's pure fact and drawn for the eyes to see. I have said more than once that on a large scale, if the apex angle was to span for a long distance the V grind has more metal, but that's simply not applicable in real life on a real knife, edges are not long enough for that concept to even matter. I'm happy to just step back since it's clear some of us are sticking to one mathematical example about the very peak of the edge angle being followed in a straight line for an infinite distance. While a couple of us are basically talking about a small real world knife with a convex grind.
 
Mick_1KRR said:
My goodness. Some people just cannot understand the concept. You can cling to your mathematical equation all you like, because you are only seeing HALF the picture. YES the angle and the apex IF FOLLOWED forever on a straight line will be thicker behind the edge on the V grind. BUT - whos knife edge bevel continues forever and ever in a straight line??? In real life, when we are talking knives and ACTUAL USE when it comes to cutting geometry, the convex edge allows more metal behind the edge over a short distance because of the difference between the start of the cutting edge angle and and the angle it actually is when you connect the two points with a straight line. Here's a picture i drew for you so you can grasp what we are trying to say regardless of your mathematical point. In a mathematical sense if you measure forever in a straight line, the V grind wins. IF you measure a REAL KNIFE IN REAL LIFE - the convex wins for metal behind the edge between the shoulder and the cutting edge. End of story. Now you can argue the V edge will have more metal if you continue the apex angle in a straight line forever and ever, but the fact is that is a moot point when put into real word cutting geometry/performance examples. Nobodys knife continues in a straight like forever, you are clinging to that mathematical fact to side step the real word use point i'm trying to make.

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^^
This! Makes sense.

And I'm NOT gonna sit down and watch some australian dude talk me to death on youtube about angles for 30 mins!! :D
 
marcinek said:
...that is somehow not subject to the laws of geometry and mathematics.
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FortyTwoBlades said:
Nobody said that, though...
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This picture is the only point i am trying to make, and you can't argue with it, because it's right here for you to see. Are you both honestly trying to say the picture on the left has more metal between the shoulder and the apex of the edge? If so then i really don't know what else to say. When 2 points are connected, one with a straight line and one with a curved line, the curved line is always longer, just like taking the long way to drive home instead of going down the straight highway. There is more room for metal behind the edge between the 2 points.
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