CONVEX EDGE, why is it so popular?

Tai Goo

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There is no such thing as "edge geometry", only what goes on behind the leading edge,... "blade geometry". The diagrams are interesting and represent points of references. However, the variations between them and overall blade geometries are infinite,... and each has it's place and purpose. There is no one best geometry for everything...

The "edge" has no mass of it's own and is just a conceptual boudary or line that separates one thing from another. It's where one thing stops and another begins.

Dictionary.com Unabridged (v 1.1) - Cite This Source - Share This
edge Audio Help /ɛdʒ/ Pronunciation Key - Show Spelled Pronunciation[ej] Pronunciation Key - Show IPA Pronunciation noun, verb, edged, edg·ing.
–noun 1. a line or border at which a surface terminates

What the ABS prefers has mostly to do with "ABS standardized testing", geared for certain types of knives, such as flat ground bowies and camp knives... and certain applications.

It just depends what you want to cut and how you want to cut it.

I use a wide variety of geometries, but generally varying degrees of convexity behind the leading edge. With the freehand honing methods that I use, it is actually much harder, (if not impossible), to do a perfectly flat hone. Honing the primary bevels and the apex just behind a secondary bevel can be helpful in some cases.

This is just my "Edge Philosophy"... :)
 
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Both # 1. and #3. are Saber grinds. It doesn't have any thing to do with whether it is hollow(Concave), semi hollow,(Not Pictured). Flat or or Convex. Saber simply means that the grind extends from Apx 1/3 to 3/4 up the blade. Not terminating at the spine. It is for strength. Not cutting ability.

The Convex edge excels at chopping. The reason an Ax works so well for this task. In the ABS and other cutting Competition, the knife is used as an ax. or machete. It is mostly a chopping match. Not a cutting competition at all. There is no draw cut. No push cut. It is all muscle, speed, and accurate hitting of the target. Not any type of practical cutting at all for a knife other a brush cutting or clearing blade.

The Convex edge use to be considered the worst of all edges. It is a version of what some one who isn't skilled at sharpening will get without meaning to on a knife blade. Not maintaining the exact angle with each pass on a stone will unintentionally give you a very similar edge. It use to be called an apple seed edge. When Bill Moran discovered that it could be quickly applied with a semi slack belt on a belt grinder in a matter of a minute or too, Ken Warner told the world about this fantastic new edge shape. Never mind it had it had been around fo centuries. (Kinda reminds me of B. M.'sthe discovery of damascus).

Its biggest advantages are!.

1. It is the strongest edge type that is still able to cut in a respectable manner.

2. It is a no brainier for the maker. The grinder will just about grind the edge it's self. In fact you can set different radius's by how much tension you have on the tracking system that controls belt tension. It Will do the best job you ever saw of covering up a less than ideal edge profile. many makers sadly cannot, or will not take the time to make sure the edge thickness is the same from one portion of the edge to another portion. I'm not talking about thicker sections, ground on purpose, but rather blades who's edges are wavy due to either heat treating warp, or miss grinding. The Apple Seed or Convex does a fantastic job of covering up these unacceptable flaws. And it blends the blade into the cutting edge in in a smooth transition. This really helps show off Damascus, helps the looks of a hand satined blade a great deal.

3. It is a superior chopping profile. It tends to not get stuck or wedged in the cut such as when choping on a limb ot tree. However this is only an advantage with a across the grain cut. It will wedge just like any other grind in an end grain chop.

It's biggest disadvantages is that it is thick. It cannot give fine cuts. When it does get dull, most end users can only sharpen it to a normal final edge.

But most importantly, unlike what has been stated above, unless sent in to the maker, or someone else with slack belt access, it will get thicker and thicker just behind the edge. You might just as well try field dressing your Buck with a sharp Axe. Sure you can get it to shave, but it will still not cut well at all.

The one profile not shown above is the Full Hollow Grind. Unlike the Saber, it extends all the way to the spine. It will, when properly ground and sharped, out cut all other Profiles I know of. Think slice rather than chop.

The finest cutting instruments I have ever seen are fine German Straight Razors. Every one I have ever examined were Very Deep Hollow Ground. I have never once, ever seen a flat, much less convex ground, or sharpened Straight Razor.

If you want a Sharp chopper, or brush clearing tool. Convex.

If yo want wiggle your head, and it falls off sharp. Concave. Or at least Flat., Until you sharpen it one too many times. Then the Flat grind gets to be like a sharpened coal chisel. It will have to be re-ground after a lot of use. The hollow just keep going until the knife is completely worn out.
 
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I have found that no other grind performs as well as a properly executed convex grind or a flat primary grind with a convex edge. A full hollow ground certainly cannot. Hollow grinds and thin flat grinds might excell at slicing THIN material (like straight razors are required to do), but they will always have more drag when slicing thick material, like meat or cheese, and they certainly aren't the best for chopping, as has been said before. The geometry of the convex grind forces the material away from the sides of the blade while slicing or chopping, reducing drag, unlike a flat or hollow grind. The only exceptions to convex geometry's superiority in comparative testing is in slicing thin material, when a convex grind is overly thick (like many are, unfortunately), or (possibly, I haven't tested this one) when a really deep hollow grind is done while leaving the edge thick and sharpening it with a convex profile, like Jerry Hossum does.

A poorly executed convex grind will perform dismally, probably much worse than a poorly executed flat or hollow grind.

I don't find convex grinds easy to sharpen at all, taking much more time that flat or concave, but I keep a convex edge on all of my using knives because it cuts so much better.

All of the above is what I have found to be true by testing all sorts of grinds on all sorts of knives IN MY SHOP AND HOME, and my not reflect your findings/feelings.

Todd

Apologies to Tai for using "convex edge" to describe the area that is behind tha actual edge.:D
 
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Tai Goo

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It’s the acuteness and completeness of the terminating angle that determines the degree of sharpness. :)
 

Tai Goo

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The sharper the terminating angle, the less resistance and the less strength... :)
 

Tai Goo

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The thicker the cross section, at any given point,... the greater the resistance and the greater the strength. :)
 
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Given an equivalent terminal angle, a convex edge will have LESS metal behind the edge than a v ground blade. Convex ground blades are considered to have a lot of metal behind the edge only because they are typically visioned as having more obtuse terminal edge angles, as compared to v ground blades.

Comparing apples to apples (same terminal edge angle) the V ground blade will have more metal behind the edge than a convexed edge

If you don't believe me, take a piece of paper and a pencil and draw a V. Then draw a "convexed" V on top of the straight V with the same terminal angle. You won't be able to do it. If you are stubborn you will need a pencil with a big erasor, but you still will not be albe to do it.

The only way to make a convexed blade with more metal behind the edge than a V ground blade is to make the edge angle more obtuse.

Convexed blades are great cutters because the blade falls away from the edge exponentially, where the same is not true of a V ground blade. Less blade is in contact with the substrate at any particular point in time.
 

Tai Goo

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... Now, draw a cross section of a convex grind, and draw a flat grind inside of it to the same thickness at the apex (or spine).

I boggles the mind doesn't it?
 
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Sorry,

I just irks me when people talk about how a convex grind makes for a tougher blade because of more metal behind the edge, relative to a v grind.

Tai Goo, not it does not boggle the mind, because to my mind you are making an unfair comparison, as the flat V grind is at a much more accute edge angle.
 

Tai Goo

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LOL :D

Edge philosophy 101:

An edge is where one thing stops and another thing begins. The edge is neither thing but the conceptual line between the two,... the border. The edge itself has no mass of it's own. Everything has an edge. There are all kinds of edges just look around you. Some are smooth some are rough some are straight and some are crooked. When the edge of one object goes beyond the edge of another we call it a cut. When two objects try to occupy the same time and space one object must give. Every edge has more than one side. Unless the mass is clear you can't see one side from the other side. One side hides behind the other and it disappears. If you take the plane from one side follow it out and find the point where it intersects the plane from the other side, that's where the corner is.

Flat surfaces also have an edge or imaginary boundary between themselves and what ever begins where they end. If you follow the flat edge around you eventually turn the corner. The corner is the apex where two planes meet. On a rounded or spherical edge there are an infinite number of intersecting planes, angles, apexes or edges.

A round edge or wire will cut equally well in any direction to it's axis.

When making a cut, if the angle of penetration is critical a rounded edge make sense because it offers a wider variety of conceptual, apexes, corners and angles.

At the point where the two planes of the edge intersect, the edge inverts itself, disappears, swirls around and keeps on going... This is called "cutting chi".

If you look square on at a flat surface, it's hard to see the edge. If you walk around to the side to where the flat surface becomes a thin line, that's where you can see the edge best.

I decided to do a philosophical edge analysis on a 1/4 by one inch square piece of steel. First I cleaved it from a bar and filed it a little. Then I turned it around and around looking at it from all angles. I pondered it for quite a while. Where was the edge? What part was the edge? Was it the top, the bottom, the side, the side corner, the end corner or one of those places where three corners meet? Then it struck me like a bolt of lightning,... the edge runs clear around it in every direction!

A better question would have been,... "Where isn't the edge on it?".

I'd sure like to be the possum to figure that one out!

"Don't play what's there, play what's not there." Miles Davis
 
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I read that whole post. There's 3 minutes that I'll never get back.
 
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hlee,

Thanks very much! Oddly, I should've known that because I've used sharpening jigs to obtain convex edges and would set the plush-backed abrasives (usually sandpaper over foam mounting tape) at a lower angle to avoid rounding or thickening the edge. It also explains why my better freehand edges travel high up the blade. :eek:
 

Tai Goo

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I read that whole post. There's 3 minutes that I'll never get back.

Slow reader, huh?

Just kidding! :)

Seriously though,… The negative space is equally important as the positive space, but most folks never get that far.
 
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I see a confusion between edges and grinds. I keep seeing the Convex edge compared to the "V" grind.

You can have a V grind. or Flat grind, Convex grind Concave grind, on a blade. This is the bevels.

You can have the same In edges. Not only this, but you can have a combination of any of the two on a given knife. for instance. A Flat ground blade, with a flat, or V"" ground or honed edge.

Each can have its advantages, or disadvantages.

One poster stated earlier that a V grind only has one advantage. No it has many. More importantly a V hone, or edge has many advantages.

In the South, something called whittling is a favorite pastime in small towns. The best grind for this is either a full hollow, with a very shallow "V" edge, or a true Flat Grind where the flats extend all the way to the edge. Similar to a Japanese Swords edge. This is sometimes called a Zero grind. Many old timers will lay a blade flat on a stone to sharpen it. These knives are like razors. If you know anything about whittling, or carving, you know that you can't run a curl with a convex edge. it will skip out of the cut, unless you use a very steep angle in the cut. Then it will simply dig in. Ruining the cut.

Chopping isn't all that knives are used for. In fact, until just few years ago, We used Axes for chopping. I know that it is popular in the competitions and test. But knives should be able to cut. First and for-most. This includes slicing.

I don't know of any material that I cut that is thick. I don't make kitchen knives. There are cheap knives aplenty to slice the bacon.

But when a hunter skins his Deer, I want it to melt Thur the job. Not having a lot of drag caused by a thick edge.

Yes you can sharpen a Convex edge easily in the shop. For the end user in the field, it is nearly impossible. It is Superior as a chopper. And in thick cuts. I can't think of the last time I cut anything thick. But I use a knife constantly, daily. Day in and Day out. And have for most of my life. I want a thin, quick, extremely sharp knife for my personal use. If I want a chopper, I'll grab a hatchet, machete, Ax, or old bowie. But I don't, and can't carry anything like this on my person in every day life.
 
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I prefer the term "deliberate reader.":)

Michael, when I said v grind, I meant a v ground edge. I was attempting to limit my discussion to just the very edge of the blade, the "business end" so to speak.

I suspect that v ground and hollow ground blades are preferred in whittling (I'm taking your word for it, as I have no personal experience- being from Texas) because it is easier to get a very acute edge, as compared to a convex edge. And as a result, the comparislon being made is between edge bevels of differing acuteness, and not necessarily between different edge grinds. As I said earlier, at the same inclusive edge bevel angle, a convex edge will have less metal behind the edge than a v-ground edge bevel or a hollow ground edge bevel (more metal has to be removed from the same thickness of stock to create a convex edge, as compared to a v ground edge- at the same bevel angle).

My eperience with maintaining convex ground edges at razor sharpness runs contrary to yours. I have found that a block of wood, a piece of leather and a few pieces of sand paper are all that are required to keep a convex ground edge sharp. Of course, mileage can, and does vary.

I am not now, nor have I ever been, a knife maker.
 

jdm61

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Actually, on his video, Bill Moran sad that convexing a blade on a slack belt leaves it way too thick. He did it free hand if I recall correctly. The Moran that I had looked more like a knife that had been flat ground prior to heat treating and then sharpened from spine to edge using a SLIGHTLY slack belt. When I do a full convex grind on a Moran style knife, I flar grind and then convex it on a KMG rotary platen after heat treat and then "flatten" the grind out a bit if needed during hand sanding. In theory, what you end up with is an "almost zero" grind.
 
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