Convex or V edge ?

This thread just makes me want to get another Opinel no.8. I had one but it was the INOX variation and although it was a great knife, I want the carbon example. Had two actually and gifted them both.
 
Ankerson The bottom line here is that when we compensate we always give up something else in return said:
LOL,yep Jim and that rings true for just about every change we make in life.Being as perfection is pretty much non existant,( everything in life is a trade off.)Anyone that likes knives should own an Opiniel #8,it's a bargain for the price and a good example of non stainless carbon steel.
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I put this together to better illustrate what I mean:

convexvsvedge.jpg
 
crom said:
This thread just makes me want to get another Opinel no.8. I had one but it was the INOX variation and although it was a great knife, I want the carbon example. Had two actually and gifted them both.
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Mission accomplished:)
 
stoffi said:
I put this together to better illustrate what I mean:
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You're still talking around Ankerson. You need to be working with a convex edge that has the SAME edge angle at the tip. Not "practically the same," the SAME. Period. If they have the same angle, then there's not going to be a noticeable difference in cutting ability. That's what Ankerson is saying. You're still working from the "but what if I convex a v-edge" principle, which says nothing about which edge is actually better, because convexing the edge on a knife that WAS a V-edge will reduce the edge angle. If you reduced the edge angle on the same knife but kept it a V, it would STILL cut better than it did initially, assuming you do a good job at both.
 
crimsonfalcon07 said:
You're still talking around Ankerson. You need to be working with a convex edge that has the SAME edge angle at the tip. Not "practically the same," the SAME. Period. If they have the same angle, then there's not going to be a noticeable difference in cutting ability. That's what Ankerson is saying. You're still working from the "but what if I convex a v-edge" principle, which says nothing about which edge is actually better, because convexing the edge on a knife that WAS a V-edge will reduce the edge angle. If you reduced the edge angle on the same knife but kept it a V, it would STILL cut better than it did initially, assuming you do a good job at both.
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That will continue to happen also. ;)

Those steels they use in those knives is not hardened very high at all so the edges will roll pretty easy so that is what they are used to using and compensating for.

Now take a blade in a different steel at very high hardness that is ground very thin and done properly it just ain't gonna roll like that.

I have used knives at high hardness (63+) with V edges that were .005" behind the edge and sharpened to 24 degrees inclusive to cut notches, whittle even push through knots and didn't have any issues, but then that was using good technique keeping the spine of the blade in line with the edge.....

Thumb size?

I could go right though that like butter.

Just because someone isn't a bushcraft junky doesn't mean they haven't done or may still do certian things with knives and wood.

I am just one of those who doesn't see what the big deal is because to me it's not.....
 
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Ok, I agree with Ankerson that thinning a knifes edge will improve performance, that's a no-brainer. I also can understand that when you convex a 'v' edge you are thinning the edge at the same time. Got that. Where i am a little bit wary is when it comes to thinning a blade with high rockwell hardness and expecting it to do a hard days work with wood and not expect it to sustain some damage. I have a Fallkniven TK4 with 3G which is my edc, I've convexed the edge to blend better with the full convex grind (as you would say Ankerson, I've found a good compromise) so I have thinned the edge but if I had maintained the 'v' and thinned the edge to the same angle I would have less material behind the edge than the convex edge. That material helps support the edge.

I also have a Stretch in zdp 189, there are numerous threads relating to people who have tried to thin this type of knife and run into problems with chipping.

I'm all ears if you have a suggestion for a type of steel that can be thinned to the angles you have mentioned and work hard all day without any issues (then i'll put a convex grind on it and it'll be even better;))

P.S. I'm not a bushcraft junkie, working with wood throughout my day can be part of the job and consequently I'm careful with my knife for my protection too!:)
 
I prefer a convex edge because I'm good at it. I can get it hair whittling, and it has the cosmetic benefit of maintaining the finish of the blade when sharpening the edge. But sharp is sharp no matter how it gets there, do what works for you.
 
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crimsonfalcon07,

having a convex and v-edge at the exact same angle is a paradox. It cannot be so. It can only be practically or close to the same, because the convex shape is curved and the v-edge is straight. Therefor, there is no "exact same. period." angle. You can't call a straight line and a curved line the same. That's why I'm giving an example of where they are practically the same to the eye at the very edge (cutting edge). I give an example of what it could look like under a microscope to illustrate that these two lines cannot ever be the same. What happens after the edge however, is much more drastic and that is the part which really helps the convex in cutting ability. The very edge is so minimally different in practical terms, that they are as close to being the same at the edge as they can be (in my example), but not behind the edge.

marcinek,

grow up.

Ankerson,

it doesn't matter what steel we use to test geometry, as long as we use the same steel for each grind.

I'm not trying to say that v-edges are crap or anything. I'm simply giving the OP my opinion and explaining why I believe that convex edges and convex zero grinds excel in bushcraft over v-edges. Why are bullets, airplanes, racecars and boats shaped like they are? Because the more slick they are, the less resistance they have when going forward. A shoulder on a knife edge offers resistance in the cut.
 
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avoidspam said:
but if I had maintained the 'v' and thinned the edge to the same angle I would have less material behind the edge than the convex edge. That material helps support the edge.
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no, at the same angle, the convex edge is the one that is thinner.

stoffi, at a microscopic level, where the apex of the edge is measured, you are not going to have convexity to any level you are suggesting. We are talking about a few microns of steel, with an edge radius of half a micron or less for a polished edge. This is where an edge is sharp and where a dull edge reduces your cutting efficiency. There is no curvature here directly and purposefully applied by a differing sharpening method, and nothing that will have such dramatic or even perceptible effects on cutting force.
 
avoidspam said:
but if I had maintained the 'v' and thinned the edge to the same angle I would have less material behind the edge than the convex edge. That material helps support the edge.
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If you kept the same angle you thinned it out by convexing it. ;)

So if there is more material as you say then the angle has changed to a steeper angle than what it was when it was a V edge.

That would have the same effect as changing from a 30 degree inclusive edge to a 40 degree inclusive edge.

So what is really happening is the edge is stronger, but with a steeper angle so cutting efficiency goes down.

If you convex an edge that is already rolling and are keeping the same angle then it would roll even easier than before because you are removing even more metal weakening the edge even more.

That is the same as starting out with an edge that is rolling at 30 inclusive and then reprofiling it to 20 degrees inclusive and saying it's stronger.....

So that is why the hype and urban legends that have been coming out of the bushcraft crowd just don't hold water and never have, and they never will. ;)

avoidspam said:
I also have a Stretch in zdp 189, there are numerous threads relating to people who have tried to thin this type of knife and run into problems with chipping.
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Oh I forgot, you aren't going to get what you are really looking for in a production blade sorry and definitely not at the price those BC knives run at typically.
 
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stoffi said:
crimsonfalcon07,

having a convex and v-edge at the exact same angle is a paradox. It cannot be so. It can only be practically or close to the same, because the convex shape is curved and the v-edge is straight. Therefor, there is no "exact same. period." angle. You can't call a straight line and a curved line the same. That's why I'm giving an example of where they are practically the same to the eye at the very edge (cutting edge). I give an example of what it could look like under a microscope to illustrate that these two lines cannot ever be the same. What happens after the edge however, is much more drastic and that is the part which really helps the convex in cutting ability. The very edge is so minimally different in practical terms, that they are as close to being the same at the edge as they can be (in my example), but not behind the edge.

marcinek,

grow up.

Ankerson,

it doesn't matter what steel we use to test geometry, as long as we use the same steel for each grind.

I'm not trying to say that v-edges are crap or anything. I'm simply giving the OP my opinion and explaining why I believe that convex edges and convex zero grinds excel in bushcraft over v-edges. Why are bullets, airplanes, racecars and boats shaped like they are? Because the more slick they are, the less resistance they have when going forward. A shoulder on a knife edge offers resistance in the cut.
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I really don't think you are understanding exactly what you are doing and why those edges are stronger.

If the edge is stronger in the end then the angle is steeper than the V edge, not the other way around, you can't remove metal and make it stronger, it's just not going to happen in the real world.

I am not an aerospace guy, but those things you are talking about and the main reason they are shaped the way they are is for strength and efficiency combined so the reason isn't what you think it is.

Aerospace doesn't translate to knife edges sorry, that's another myth and urban legend.....
 
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avoidspam said:
Ok Ankerson, you're piqued my curiosity now, what steels are you working with?
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Lately in CUSTOMS they are or have been S110V, K294, M390, ELMAX, N690 and 10V all at high hardness except for N690 (61 HRC), all FFG and VERY thin ranging from .004-.010" behind the edge.

That doesn't translate or compare to production blades in any way though and is taking into count proper cutting techeque.

For general BC use I would go thicker like .015" behind the edge though to add more lateral strength.
 
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stoffi said:
I put this together to better illustrate what I mean:

convexvsvedge.jpg
Click to expand...

Good diagram but you forgot to factor in the way stress builds up in a structure. With no shoulders on a convex, there is nowhere for stress to build at a single point, as the stress is distributed more evenly across the materials, so the overall effect is of a more durable edge. It's why round tube is stronger than RHS for the same wall thickness and similar cross sectional area and also how arches get their strength.
 
parbajtor said:
Good diagram but you forgot to factor in the way stress builds up in a structure. With no shoulders on a convex, there is nowhere for stress to build at a single point, as the stress is distributed more evenly across the materials, so the overall effect is of a more durable edge. It's why round tube is stronger than RHS for the same wall thickness and similar cross sectional area and also how arches get their strength.
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That's NOT how it works when talking about knife blades. ;)

To make the edge stronger one or all have to happen:

Raise the HRC hardness

Increase the edge angle

Use the stronger steel

Make the steel thicker
 
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