What Are The Advantages of a Convex Grind?

Can I thin behind my convex edge by flattening it, without changing the edge angle, and without shortening (raising) the primary grind?
 
Y'all are making my head hurt.

To answer the OP:

My fixed blade knives are almost 50/50 convex and scandi grind with a micro bevel. I like the scandi for working wood like carving notches, making tent pegs, etc. I consider this light work. For what I call heavy work (cutting through things, chopping, cleaning game), the convex is better. Why? Personal preference based on how I use my knives. Your mileage may vary.
 
jpm2 said:
Can I thin behind my convex edge by flattening it, without changing the edge angle, and without shortening (raising) the primary grind?
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Yes but it's not something i would imagine you would ever do. It would be basically trying to blend the edge into the blade grind in reverse. Rather than doing a regrind of the knife to think it behind the cutting edge and then putting the convex on, kind of like a zero grind.
 
Mick_1KRR said:
This is a very good pic which also reinforces what i said as well as your point also. As i said numerous times, at the very edge if you continued on a straight line the V grind will always be thicker. But, if you treat each of those left and right corners as knife edges, which one is actually realistic? One is a usable convex, and the other is basically a sharpened cube 90 degree angle for a knife edge. Now i've edited your picture to show what im talking about, and basically the only point i have been trying to make - If a normal, usable convex was put on a knife with a normal hollow grind or saber ground blade geometry (not a zero grind convex from the spine) then the convex will always contain more steel behind the edge, even tho it would be a chunky edge. I'm talking shoulder to apex being an even distance for the entire primary edge bevel. The mathematical formula has always been correct, but it hasn't been the focus of the example i have been trying to explain. Either way guys, i'ts been a good discussion, no chips on any shoulders, i enjoy this kind of thing, we're both correct, we're just making different points.
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Well, my picture is asymmetrical. I apologize. I now realized that the unit of measurement is 4:5 which should be 1:1 (aka 5:5). This is an accident on my part, however it does not advance your theory. You are simply not understanding basic geometry.

Shoulder-to-apex is irrelevant. Your primary convex bevel will still have less behind the edge if it were convex.

And no, we are not making different points. You are totally misunderstanding geometry. I can prove so after I take a shower and allow time to draw this out.

Geometrical and mathematical proofs were my niche in college. Better buckle up!
 
brancron said:
These threads always turn into geometry fights.
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Yes, geometry fights, arguments about terminology that is ambiguous or hard to explain, and small diagrams that may not illustrate the point very well. I've read lots of these threads and they always turn out the same way. I don't think anybody ever changes their opinions.

I'm an engineer so I can outmath most of you. I can also draw pretty diagrams in AutoCAD, but I'm staying out of this argument.

Most of my knives have normal v-grinds and they are easy for me to sharpen. I like the looks of the shallow convex grind of my Blackjack Classic for instance. I have a Ratmandu with a convexed edge but haven't tried sharpening it yet. I had another covex edge knife and despite watching many videos and trying numerous times, I could not sharpen it with sandpaper and a mousepad. So I'm not sure I like convex edges to use. If I could learn the sharpen them I might like them better.
 
Blues Bender said:
Well, my picture is asymmetrical. I apologize. I now realized that the unit of measurement is 4:5 which should be 1:1 (aka 5:5). This is an accident on my part, however it does not advance your theory. You are simply not understanding basic geometry.

Shoulder-to-apex is irrelevant. Your primary convex bevel will still have less behind the edge if it were convex.

And no, we are not making different points. You are totally misunderstanding geometry. I can prove so after I take a shower and allow time to draw this out.

Geometrical and mathematical proofs were my niche in college. Better buckle up!
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I appreciate what you're trying to do, but im not misunderstanding anything, i know exactly what you're saying (and i agree with the theoretical part), i'm not new to this. You are going to draw up something that has a convex much thinner than the V edge, BUT, its not going to join into the blade grind like a normal knife would, it will be a lower angle but join into the blade grind the same way that a zero grind convex would. which is NOT my point. The edit i did on your picture explains my point, but of course you can then go and thin out the convex to match the V grind which will then make the V grind have more metal. It's a back and forth game now.

Think about this, here is a real world example. A Chris Reeve Sebenza arrives at your door, they have a very thin hollow grind as it is, but it also has a convex edge bevel since that's how they come from their factory, much more convex than say spyderco or benchmade. Now, they don't always seem to cut so well, and like many people, they prefer a V edge on their Sebenza, so they put it in a guided system (wiked edge, edge pro) whatever, and apply a V edge but keep the exact same edge bevel thickness to not change the look of the edge too much. Result - the knife seems to cut through material much better. Why is this? because the V grind is now much less obtuse than the factory convex. I've seen it and done to countless knives for years and years. If the Sebenza came with a much wider bevel that allowed for a much thinner convex edge it would slice great tho, but it would be extremely thin behind the edge due to how thin the hollow grind already is and how high the convex has to go up the blade to match an equivalent V grind.
 
You're conflating visual bevel width with edge angle. They are absolutely not the same thing.
 
What if it's a reprofiled V edge that has been convexed blended into a flat grind then has a V microbevel put on it :eek::confused::D

IMG_20170311_123207-X2.jpg
 
I feel like Bill Nye at a creationist convention every time these threads pop up.

A V edge will have less material behind the edge than a convex would when both are held at the same angle, but only because the convex will be more obtuse at the apex.

Mick, you keep arguing that point, but it's an irrelevant one. Yes, you're right about it, but you don't cut anything with the shoulder of a bevel. The shoulder merely moves material away and is relevant only in specific situations.

The apex is always relevant because it always does the cutting. When a convex edge has the same tangent angle, because we're being that anal about it, at the apex as a V edge, the V will have more steel behind the edge and be more stable.

Yes, it will have a sharper transition into the primary grind and be more prone to wedging, but the apex, the edge will be more stable.

profiles.gif


Why whomever made this image gave the V edged knife much thicker stock is beyond me, but it still illustrates the point well.

When the apex angles are the same, a convex grind falls away from that angle as you progress upward on the blade, eventually blending with the primary grind. The V edge maintains that same angle all the way out until it simply runs out material, at which point you get a sharp shoulder where it transitions into the primary grind.

To answer the OP:

The V edge is more stable than a comparable convex, but the convex is more forgiving in maintenance and will slice better.
 
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Is it considered a convex grind if the edge curves up and meets but does not seamlessly merge with the primary bevel?
 
FortyTwoBlades said:
You're conflating visual bevel width with edge angle. They are absolutely not the same thing.
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I don't even have any words anymore. Just tired of terminology word twisting in order to side step a tiny point i was making. I've been in this game a stupidly long time mate, nearly 2 decades of sharpening and experience with edges, re-grinds and geometry of all sorts. I know what edge angles are in relation to the visual bevel. Just because you interpret a few words in a way that seems different to what i'm saying, you assume i've somehow confused and mixed up 2 basic principles when it comes to edge geometry. It's almost like there's a willing ignorance in the air sometimes. I'm out, thread has crumbled anyway. This forum is much easier to be a part of when you're just lurking sometimes. Good luck with everything OP.
 
Mick_1KRR said:
I appreciate what you're trying to do, but im not misunderstanding anything, i know exactly what you're saying (and i agree with the theoretical part), i'm not new to this. You are going to draw up something that has a convex much thinner than the V edge, BUT, its not going to join into the blade grind like a normal knife would, it will be a lower angle but join into the blade grind the same way that a zero grind convex would. which is NOT my point. The edit i did on your picture explains my point, but of course you can then go and thin out the convex to match the V grind which will then make the V grind have more metal. It's a back and forth game now.

Think about this, here is a real world example. A Chris Reeve Sebenza arrives at your door, they have a very thin hollow grind as it is, but it also has a convex edge bevel since that's how they come from their factory, much more convex than say spyderco or benchmade. Now, they don't always seem to cut so well, and like many people, they prefer a V edge on their Sebenza, so they put it in a guided system (wiked edge, edge pro) whatever, and apply a V edge but keep the exact same edge bevel thickness to not change the look of the edge too much. Result - the knife seems to cut through material much better. Why is this? because the V grind is now much less obtuse than the factory convex. I've seen it and done to countless knives for years and years. If the Sebenza came with a much wider bevel that allowed for a much thinner convex edge it would slice great tho, but it would be extremely thin behind the edge due to how thin the hollow grind already is and how high the convex has to go up the blade to match an equivalent V grind.
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All things being equal, convex has less material. Tangency is the key term that you are not understanding. A 40° bevel will have less material when convex. Each bevel on a V-grind must be looked at as a right angle in order to translate it to a convex edge.

The way you are looking at this (with a convex edge being wider) is not correct. You are not matching the same angles. If a convex edge is wider than a V, then the convex edge is held at a more obtuse angle.

2EBECD4C-C3F4-4DDF-BF58-4A2FEA98DD02_zpsroo8hpti.jpg
 
Mick_1KRR said:
I don't even have any words anymore. Just tired of terminology word twisting in order to side step a tiny point i was making. I've been in this game a stupidly long time mate, nearly 2 decades of sharpening and experience with edges, re-grinds and geometry of all sorts. I know what edge angles are in relation to the visual bevel. Just because you interpret a few words in a way that seems different to what i'm saying, you assume i've somehow confused and mixed up 2 basic principles when it comes to edge geometry. It's almost like there's a willing ignorance in the air sometimes. I'm out, thread has crumbled anyway. This forum is much easier to be a part of when you're just lurking sometimes. Good luck with everything OP.
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Don't leave! We are trying to teach you something:(

:rolleyes:
 
One thing we can all agree on......Laurence out & out wins the thread by a mile!!!
Those spandex tights describe a convex edge MUCH better than those silly diagrams!!!
Good job Laurence!!
Joe

Rhinoknives1 said:
I like my own Custom knives that I make to have a Convex Grind & and Convex edge because they Ffffing Cut! And also really look bad Ass in tight Spandex Yoga pants!



Nuff!View attachment 710584 Said!! LOL!
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