What's tougher a scandi or convex edge?

[gine]

It's because they are parroting what they have been told and the marketing BS along with the fact they just don't understand what is really going on with the angles....

They are told or have read that a convex is stronger so it has to be thicker right?

It's only confusing because of the marketing BS that is spread in an effort to sell more knives and people buy into that crap and actually believe it......

You are entitled to your opinion, however, I couldn't disagree more. I do not buy into the marketing hype and bs whatsoever.

 

[marcinek]

Nice diagram, however I believe you have shown two extremes. A true convex is curved all the way to the edge. In your diagram on the right, you show the convex curve flattening out. In actuality a convex maintains it's curvature all the way to the center point. The halfway point between your two diagrams would be a more accurate description.

A halfway point would still have the convex edge outside the black vee. Giving it a larger edge angle.

Actually the picture on the right is generous....it does flatten out a bit making a convex edge appear to have more steel behind the edge than it actually does.

That said, it is a very accurate picture showing what knocking the shoulders off a vee grind looks like...which I believe was the intent.

 

[Big Mike]

Of course there is. But the subject at hand is what grind is stronger. And if by stronger we are talking about amount of material behind the edge, than for a given edge angle, "flat" has more material behind the edge.

And people doing things like making up new definitions of "angle" or, in effect, saying "Hey look at that!" and pointing to attempt to change the subject don't make that simple picture FortyTwoBlades posted go away.

His diagram may be correct when it comes to putting a convex edge on an existing flat ground knife (convexing is the term he uses),

...but look at the image on the left, ...that clearly shows how a proper convex edge is done.





Big Mike

 

[Mikael W]

Agreed. And you get a larger edge angle when you convex the edge like that. And a vee grind with that same, new edge angle will have more steel behind the edge than that convex.

Yes I sure agree about that!
I also think we both know that this new vee grind will take more force to cut through a piece wood than the convex, but that's basically not the Q here.

By giving the convex edge enough metal to support the cutting edge, it will both be strong and cut with less effort than the corresponding FFG + bevel.

A convex is a compromise between a vee grind and a FFG + bevel.

So perhaps we are not discussing so much about strenght, but more of cutting performance?



Regards
Mikael

 

[Moses2792796]

It seems to me that throughout this thread people are arguing different points, without realizing that they are comparing different things. I think a lot of the confusion arises because some people are thinking abstractly, whilst others are thinking more practically about how these principles are really applied to knives. There are so many variables to take into account and people seem to pick and choose which ones to acknowledge depending on the point they wish to make.

Having said that I think there should be a few basic facts that everyone SHOULD be able to agree on.

Assuming that the stock is the same thickness, the blade is the same width (in other words the edge is the same distance from the spine), and both knives are zero ground, a convex will be thicker than a flat grind.

On the other hand, assuming that the edge angle is the same, a flat grind will be thicker than a convex, no matter what.

It depends on whether you are working the the stock thickness towards the edge (figuratively speaking), which is a practical point of view, or from the edge angle towards the spine, which is abstract since we are necessarily then talking about two different knives. I don't think the picture used by FortyTwoBlades is accurate since usually when you convex an edge, the edge will be ground back a short distance, reducing the distance to the spine and increasing the angle. Hence it will look more like the example on the left, except it will fit inside the original profile. I also think people are forgetting to mention the point that the curved surface of a convex edge is more stable than a flat surface, hence even a thinner convex edge might have improved edge stability over a flat bevel, although this is speculation on my part.

 

[FortyTwoBlades]

A halfway point would still have the convex edge outside the black vee. Giving it a larger edge angle.

Actually the picture on the right is generous....it does flatten out a bit making a convex edge appear to have more steel behind the edge than it actually does.

That said, it is a very accurate picture showing what knocking the shoulders off a vee grind looks like...which I believe was the intent.

Precisely. And the proportions are deliberately greatly exaggerated because if I didn't do that then folks wouldn't be able to see the difference between the two (although you'd feel it in use). The whole point is to clearly show what's going on. And the edge IS a continuous curve on the right example. The magnitude of the curvature simply tapers of to a much more gradual one as it approaches the edge! It was drawn with only a single line segment using a bezier tool in GIMP to produce the curve. :thumbup:

His diagram may be correct when it comes to putting a convex edge on an existing flat ground knife (convexing is the term he uses),

...but look at the image on the left, ...that clearly shows how a proper convex edge is done.

Big Mike

But the one on the left would comparatively cut like crap... >_>;;

I don't know about you, but I can use thin machetes with convexed edges that have an effective edge angle of around 15 degrees per side without ANY damage whatsoever, even when repeatedly smashing the edge into knots. And we're talking a simple carbon steel of only about 55 RC and yet there's not any chipping OR rolling in spite of the thin geometry. I think folks just need to learn how to use a tool hard instead of abusing a tool hard, and be aware of exactly what kind of punishment thin steel with the right heat treatment can take. Hardness needs to stop being the holy grail we all chase after, and a more holistic approach adopted instead. There's definitely a minimum hardness that's appropriate for most tools, but you don't want to go overboard on the other end either. Neither too much nor too little of any aspect of a function/use-built design is what separates the wheat from the chaff, so to speak. In my opinion, at least.

I don't think the picture used by FortyTwoBlades is accurate since usually when you convex an edge, the edge will be ground back a short distance, reducing the distance to the spine and increasing the angle. Hence it will look more like the example on the left, except it will fit inside the original profile. I also think people are forgetting to mention the point that the curved surface of a convex edge is more stable than a flat surface, hence even a thinner convex edge might have improved edge stability over a flat bevel, although this is speculation on my part.

In my opinion, if you're convexing an edge like you describe then you're doing it wrong. If you really want extra strength then just sharpen a linear edge at a more obtuse angle. Again, you'll have more steel in the edge shoulder vs. a convex of equal edge angle.

 

[marcinek]

I also think people are forgetting to mention the point that the curved surface of a convex edge is more stable than a flat surface, hence even a thinner convex edge might have improved edge stability over a flat bevel, although this is speculation on my part.

They are "forgetting" to mention it because, as you say, it is pure speculation, i.e., made up.

They are also forgetting to mention that flat grinds shoot out rainbows and smell like freshly-baked cinnamon rolls.

 

[marcinek]

...but look at the image on the left, ...that clearly shows how a proper convex edge is done.

Yes. It does show how a convex edge is ground if it is not made by knocking off the shoulders of a vee grind.

A convex edge with a larger edge angle than than the vee grind shown in black. Tangents, people...tangents.

In layman's terms, imagine the black and red lines are the trajectories of planes landing at the point where the sides meet. Which plane is coming in less steeply? The red one. It has a smaller angle between its approach and the ground. And...here is the key point....a larger angle between its approach and vertical. That is the angle we are talking about. That's the edge angle.

Now you can talk about choices and all this other handwaving/misdirection until the cows come home....that's great.

But:

1) The topic of this thread is which grind is tougher.
2) If tougher is based on "more steel behind the edge"...then flat is tougher for a given angle.

 

[Mikael W]

Yes. It does show how a convex edge is ground if it is not made by knocking off the shoulders of a vee grind.

A convex edge with a larger edge angle than than the vee grind shown in black. Tangents, people...tangents.

In layman's terms, imagine the black and red lines are the trajectories of planes landing at the point where the sides meet. Which plane is coming in less steeply? The red one. It has a smaller angle between its approach and the ground. And...here is the key point....a larger angle between its approach and vertical. That is the angle we are talking about. That's the edge angle.

Now you can talk about choices and all this other handwaving/misdirection until the cows come home....that's great.

But:

1) The topic of this thread is which grind is tougher.
2) If tougher is based on "more steel behind the edge"...then flat is tougher for a given angle.

If by flat You mean FFG + bevel and completely leave out cutting performance, then yes.
Not a knife I would like!


Regards
Mikael

 

[stabman]

Too many people severely overthinking things.

I sharpen it till it cuts, then I go cut stuff.
When it gets dull, I sharpen it again.
And the edge hasn't fallen off, nor has the world ended.

And the strongest edge is the one I put on a knife, because of the triple dose of awesome that imparts.

 

[Mikael W]

I agree with Mikael, my personal experience is what matters to me.


The point that's being missed in this discussion is that there is room for all types of different grinds and edges.

Find the edge that works for the task at hand and you'll be a happy camper.


There's no wrong or right in this discussion, we all strive for better performing knives.

Personally, I tweak every knife I have until it performs to my satisfaction.

As I stated earlier in this thread, debating the subject is fine, but getting out and trying different grinds and edges is the best way to figure it out for yourself.




Big Mike

Mike, You and I have since long been on the same page regarding convex blades and edges!

I agree with Your statement above and try to have an empiric mind around knives.
The best way is to actually use and sharpen our tools in real world use!
This is what I do right now this last weekend of vacation, before work start on Monday.

I'm preparing a new custommade knife that was delivered yesterday.
It's a fully convexed blade with convex secondary bevel.
The maker is Seved Hjelm and my wish was that he made a typically Swedish fixed beltknife, for everyday use.

So this is what I'll be evaluating in the nearest future.

Simple, functional and very Convex!


Regards
Mikael

 

[FortyTwoBlades]

If by flat You mean FFG + bevel and completely leave out cutting performance, then yes.
Not a knife I would like!


Regards
Mikael

By flat he means a "V" (aka linear) edge bevel vs. a convex edge or equal effective edge angle.

Seriously, though, I agree with stabman that a lot of folks really think too much about this topic...but at the same time not enough. Either don't worry about it at all, or think about it a freaking TON until you realize all the time you wasted thinking about it. Drink deeply from the well of knowledge, because a little knowledge is a dangerous thing. Or just save yourself the trouble and accept that a convex is thinner at equal effective edge angle vs. a linear edge bevel and leave it at that. Because the deeper you dig the more you'll realize that's how it is; I really don't want to make what can sound like such a conceited statement, but it's really as simple as that. I mean, you can actually see it in the diagrams I posted.

Another way to think about it is in terms of fluid dynamics. Imagine a boat going through the water, with a certain given angle to the bow and width at the stern. Which will go through the water better? The convex. But which will have the greater internal volume? The one with a "V" geometry to the bow. The reason for the convex one going through the water easier (and the reason why basically every boat EVER is convex even though it's easier to build a V-shaped bow) is the same reason a convex has improved thinner geometry that smoothly passes through the water it displaces. However, if we could somehow lock the bow of that boat in a massive vice and try to snap it off, presuming we filled the whole boat with something like lead or concrete so it wasn't hollow, the V-shaped one would be stronger because of the increased internal volume at the point of strain.

 

[festerfromnzed]

It is my understanding (and experience) that a full convex edge is stronger...That is why competition axes are ground this way..not only because it is less likely to bind in the wood......FES

 

[FortyTwoBlades]

It is my understanding (and experience) that a full convex edge is stronger...That is why competition axes are ground this way..not only because it is less likely to bind in the wood......FES

They're ground that way because they cut better for their effective edge angle. Hence "competition cutter."

 

[Mikael W]

By flat he means a "V" (aka linear) edge bevel vs. a convex edge or equal effective edge angle.

Seriously, though, I agree with stabman that a lot of folks really think too much about this topic...but at the same time not enough. Either don't worry about it at all, or think about it a freaking TON until you realize all the time you wasted thinking about it. Drink deeply from the well of knowledge, because a little knowledge is a dangerous thing. Or just save yourself the trouble and accept that a convex is thinner at equal effective edge angle vs. a linear edge bevel and leave it at that. Because the deeper you dig the more you'll realize that's how it is; I really don't want to make what can sound like such a conceited statement, but it's really as simple as that. I mean, you can actually see it in the diagrams I posted.

Another way to think about it is in terms of fluid dynamics. Imagine a boat going through the water, with a certain given angle to the bow and width at the stern. Which will go through the water better? The convex. But which will have the greater internal volume? The one with a "V" geometry to the bow. The reason for the convex one going through the water easier (and the reason why basically every boat EVER is convex even though it's easier to build a V-shaped bow) is the same reason a convex has improved thinner geometry that smoothly passes through the water it displaces. However, if we could somehow lock the bow of that boat in a massive vice and try to snap it off, presuming we filled the whole boat with something like lead or concrete so it wasn't hollow, the V-shaped one would be stronger because of the increased internal volume at the point of strain.

Leave it sounds like the best choice!
I'm using knives, I don't calculate them!
However, I used to build boats and I can follow Your thinking and there's a lot of convex, concave and flat surfaces in a boathull.
Let's leave the boats behind also, as this might send me off thinking of NACA wingprofiles for keel and rudder.
You can probably find analogys with convex knives in the 4 figure series and the 6 figure series of wing profiles, but we better leave that as it is.

I believe the OP has got an answer to his original Q and that is fine with me.
Now, I have a new knife to learn about!


Regards
Mikael

 

[festerfromnzed]

They're ground that way because they cut better for their effective edge angle. Hence "competition cutter."

YES....And they cut better because they hold their edge longer because convex edge is stronger??....Not looking to argue this point,just clarify it.....................FES

 

[FortyTwoBlades]

YES....And they cut better because they hold their edge longer because convex edge is stronger??....Not looking to argue this point,just clarify it.....................FES

Nope--they cut better because they don't have to displace as much material behind the edge during the cut. Less energy of the swing is lost due to having to push matter away from the blade. They "hold their edge longer" due to their steel and heat treatment. As the saying goes, geometry does the cutting and steel/heat treatment determines how long. Technically a thicker edge will actually dull more rapidly. Imagine two stacks of blocks, each three rows high. One stack, from bottom to top, is 3 blocks, 2 blocks, then 1 block. The other one goes 5 blocks, 3 blocks, then 1 block. This represents the fully sharpened edges at different slopes. One block (the apex of the edge) wears away and is removed from each of the stacks. You now have one knife with an edge that's 2 blocks wide, and another knife with an edge that's 3 blocks wide.

Competition cutting knives take much of their lateral strength from being both thick at the spine and broad in the blade. You can still have a knife that's quite thin near the edge if you make it wider--the angle of the primary grind keeps extending the wider you go, increasing your potential maximum spine thickness for that grind angle. The wider it is the more resistant to flexion it is, as well--if you have two strips of spring steel, one 2" wide and one 3" wide, both of them 1/8" thick, the wider one will be harder to flex.

 

[festerfromnzed]

42.....thanks for that................FES

 

[FortyTwoBlades]

You're very welcome!