What's tougher a scandi or convex edge?

[goodeyesniper]

I guess what I meant to ask was- If you had a scandi blade and a convex blade, same steel, same edge angle and thickness at the cutting portion, and you performed the exact same tasks (we'll say feather sticking and power cuts into wood), which blade would dull, chip, roll and need to be touched up more often?

I'm pretty sure scandi is the answer. I just wanted to hear a scandi guy differ.

the Scandi will be thicker behind the edge if you were matching edge angle and spine thickness. (see Marcinek's picture) so theoretically the convex will fail first because it has less material behind the edge.

the problem is that most people are comparing 2mm thin Mora knives, to chunkier "survival"knives with a convex grind.

 

[Ankerson]

the Scandi will be thicker behind the edge if you were matching edge angle and spine thickness. (see Marcinek's picture) so theoretically the convex will fail first because it has less material behind the edge.

the problem is that most people are comparing 2mm thin Mora knives, to chunkier "survival"knives with a convex grind.

The thinner the edge the weaker it will be so yeah the convex edge will usually fail 1st as it has less steel behind the edge, it's basic physics.

But then that depends on what one would be trying to cut that the edge would fail in the 1st place.......

It is laughable that people compare those $10 knives (Mora's Etc) to more expensive knives with better steels when it's really the overall blade and edge geometry that makes them perform, thinner cuts better than thicker.

It's really the lack of understanding of what is really going on and or comprehending why things work the way they do so they just parrot the marketing BS and pass on bad information as so call truth.....

 

[Shotgun]

I've used both and haven't had rolls or chips unless hitting something hard like rocks and metal. Then both will chip and roll. As for which will dull faster, that's a matter of the steel and heat treat IME.

I prefer convex because it gives you the same edge angle as the scandi while being thinner behind the edge. I guess it would be weaker but this "weakness" hasn't resulted in any real world failure for me. So a convex works better for what I do. I think I would phrase it like this: A convex grind gives me better performance while having the same edge stability as an equivalent(edge angle) scandi.

 

[james terrio]

Assuming all other factors are equal, more steel is more stronger. Period.

 

[gine]

It comes down to how much material is supporting the edge. Apple seed grind is rounded behind the cutting edge, so it would be thicker and have more strength. This is if both blades were the same thickness and ground the same and made from the same steel. If all grinds were zero ground, hollow being thinnest, flat being middle, and convex being the thickest.

 

[Joe Duder]

Thanks for all the input guys. I like the way this is going.

 

[Ankerson]

It comes down to how much material is supporting the edge. Apple seed grind is rounded behind the cutting edge, so it would be thicker and have more strength. This is if both blades were the same thickness and ground the same and made from the same steel. If all grinds were zero ground, hollow being thinnest, flat being middle, and convex being the thickest.

Actually the order would be the following using those variables.

Hollow, Convex, Flat.

That's keeping everything the same, one isn't adding metal by convexing the edge, you are thinning the edge out even more, think FFG with the corners knocked off...... That's thinner......

That's unless the angle is increased therefore the resulting convex edge would be thicker, but the trade off would be less cutting efficiency due to the increased edge angle.

 

[chiral.grolim]

If, by toughness you mean material behind the edge, then the answer is flat. Or flat scandi.

Draw a vee. Draw a convex edge that fits inside it. Draw a flat ground edge that fits inside it. Those two will have the same edge angle. The flat will be thicker. It has more material behind the edge, despite what any convex edged knife maker has said.

Its geometry. Geometry doesn't lie.

FALSE.

Convex: having a surface that is curved or rounded outward

Geometry doesn't lie, but people do, or they are just confused. See this post: http://www.bladeforums.com/forums/s...ck-vs-thin-comparison?p=11852440#post11852440

By the definition of the word "convex", it has more metal behind the edge, i.e. more structural support. The corresponding flat edge is always thinner, it must be, it cannot be otherwise given the language used and the laws of mathematics.

A convex-edge established by knocking the bevel shoulders off is certainly thinner than the previous flat grind but is THICKER than the new flat-grind would be at the same bevel height. If you ignore bevel height or thickness, you are not comparing similar geometries.

 

[Ankerson]

FALSE.

Convex: having a surface that is curved or rounded outward

Geometry doesn't lie, but people do, or they are just confused. See this post: http://www.bladeforums.com/forums/s...ck-vs-thin-comparison?p=11852440#post11852440

In that post you linked to the edge geometry is increased... Edge angle is increased..... That's why it's thicker in that post.

Not the same as keeping everything the same and not changing the edge geometry where in the process of convexing the edge MORE metal would be removed behind the edge so it would be thinner than a FFG.

Keeping the same relative edge geometry the order is:

Hollow, convex and flat from thinnest to thickest.

 

[chiral.grolim]

In that post you linked to the edge geometry is increased... Edge angle is increased..... That's why it's thicker in that post.

Not the same as keeping everything the same and not changing the edge geometry where in the process of convexing the edge MORE metal would be removed behind the edge so it would be thinner than a FFG.

Keeping the same relative edge geometry the order is:

Hollow, convex and flat from thinnest to thickest.

The "edge geometry" is defined by bevel height and thickness. Read the entire post I linked before replying. When establishing a convex edge with the same bevel dimensions as a flat ground edge, you keep the same angle of incidence and you cannot measure the actual apex angle, this assertion by folks that you can measure that angle is both silly and impractical - it asserts that the very point of the apex has a defined angle, but it does not as it is only a point. Creating a tangent along the bevel that only intersects that apex point requires very detailed knowledge of the geometry of the curve, knowledge that no one has! Folks draw an assumed tangent to show an estimated apex angle, but the question is not about edge-apex angles but edge BEVEL angles. The bevel is established NOT by the angle at the apex but by the angle of incidence or, instead, bevel height and thickness. THAT is geometry. The rest is nonsense.

 

[Mikael W]

Actually the order would be the following using those variables.

Hollow, Convex, Flat.

That's keeping everything the same, one isn't adding metal by convexing the edge, you are thinning the edge out even more, think FFG with the corners knocked off...... That's thinner......

That's unless the angle is increased therefore the resulting convex edge would be thicker, but the trade off would be less cutting efficiency due to the increased edge angle.

That's right!

This is why a cheap zerogrind Mora copes with harder materials, after getting a thickened convex edge.
At least this is my experience after using the very same 3 knives in 20 years of carpenting.

When the edge is thick enough, it start to hold up very well and will need fewer resharpenings.
It's mostly enough with just honing.

It will not be the same performance as a powdermetal at higher rc hardness and thinner edge, but O1 at rc 61, will do for a very long time.



Regards
Mikael

 

[Mikael W]

FALSE.

Convex: having a surface that is curved or rounded outward

Geometry doesn't lie, but people do, or they are just confused. See this post: http://www.bladeforums.com/forums/s...ck-vs-thin-comparison?p=11852440#post11852440

By the definition of the word "convex", it has more metal behind the edge, i.e. more structural support. The corresponding flat edge is always thinner, it must be, it cannot be otherwise given the language used and the laws of mathematics.

A convex-edge established by knocking the bevel shoulders off is certainly thinner than the previous flat grind but is THICKER than the new flat-grind would be at the same bevel height. If you ignore bevel height or thickness, you are not comparing similar geometries.

This is also right and how I look at this Q.


Regards
Mikael

 

[Ankerson]

The "edge geometry" is defined by bevel height and thickness. Read the entire post I linked before replying.

I did......

For a convex edge to be thicker behind the edge than a FFG the edge geometry would have to be increased so we are talking apples and oranges here....

That's to keep the thickness behind the edge the same say .025", the convex edges geometry would be higher than the FFG.... IE Convex 40 degrees inclusive to FFG 30 Degrees inclusive....

 

[chiral.grolim]

To recap, when comparing bevels of equal height and thickness, the order of least material support (thin) to most material support (thick) is concave (hollow), flat, convex.

"Scandi" is simply single-bevel "zero-edge", meaning that the blade has only one bevel per side and a final edge bevel was not ground into the blade afterward. That bevel may be as short as a few microns in height (some scalpels), or it may span most of the blade. But the bevel may be ground concave, flat, or convex and still qualify as "Scandi".

 

[chiral.grolim]

I did......

For a convex edge to be thicker behind the edge than a FFG the edge geometry would have to be increased so we are talking apples and oranges here....

That's to keep the thickness behind the edge the same say .025", the convex edges geometry would be higher than the FFG.... IE Convex 40 degrees inclusive to FFG 30 Degrees inclusive....

Jim, a FFG is only comparable to a FCG = full convex grind. Look at picture A again. Bevel height and Bevel-thickness, i.e. thickness behind the edge, are the same, and convex MUST BE THICKER, by the very definition of the word. Are people really having trouble with the definition of the word "convex"?

 

[Ankerson]

To recap, when comparing bevels of equal height and thickness, the order of least material support (thin) to most material support (thick) is concave (hollow), flat, convex.

The edge geometries are different in that example, the flat and hollow are the same while the convex is increased.

Or more like 15 DPS (Hollow), 15 DPS (Flat) 20 DPS (Convex)

 

[Ankerson]

Jim, a FFG is only comparable to a FCG = full convex grind. Look at picture A again. Bevel height and Bevel-thickness, i.e. thickness behind the edge, are the same, and convex MUST BE THICKER, by the very definition of the word. Are people really having trouble with the definition of the word "convex"?

The edge angle has to be increased for that to be true......

Keeping the edge angle the same relatively the convex would have to be thinner......

 

[gine]

I don't see how a convex edge is thinner then a flat if both were ground zero. Convex is oposite of hollow, concave and convex. Flat being in between the two. Big choppers are convexed for more strength, and straight razors are hollow ground for cutting efficiency. Flat grinds are the happy medium. From the grinding I have done ,convex leaves more steel behind the edge.

 

[Ankerson]

I don't see how a convex edge is thinner then a flat if both were ground zero. Convex is oposite of hollow, concave and convex. Flat being in between the two. Big choppers are convexed for more strength, and straight razors are hollow ground for cutting efficiency. Flat grinds are the happy medium. From the grinding I have done ,convex leaves more steel behind the edge.

Because the if the angles are the same the convex would have to be thinner...

To result in having the Convex being thicker the angle would have to increased for that to be possible.

 

[Ankerson]

I don't see how a convex edge is thinner then a flat if both were ground zero. Convex is oposite of hollow, concave and convex. Flat being in between the two. Big choppers are convexed for more strength, and straight razors are hollow ground for cutting efficiency. Flat grinds are the happy medium. From the grinding I have done ,convex leaves more steel behind the edge.

Yeah, you have to increasing the edge geometry for that to happen.