what are the proven advantages of a convex edge

hardheart

hardheart

Joined
Sep 19, 2001
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Numerous posts have stated that convex edges have better retention, slice more easily, are stronger, etc... but has this been verified? Has anyone sharpened a knife to a certain finish at a v-edge, done some cutting, and then sharpened to a convex edge, at the same finish and final included angle, and repeated the cutting (or vice versa)?

Comparing a factory v-edge to a user applied convex edge seems inconclusive. Who doesn't get better results over factory edges, whether it be with sandpaper/lapping film on mousepad, diamond paste loaded strop, a Sharpmaker with ultrafine stones, or an Edgepro with polishing tapes?

I no longer have jig sharpeners, so I can't check for perfectly formed v-edges, so I am asking if someone else can try, or already has.
 
I find convex edges have lower friction and cuts more aggressive than flat edge. We can all agree that convex edges outperform flat edges at any given angle, simply due to physics. It glides better, the edge is thinner.

Convex edge is also easier to make since you automagically get it if you randomly sharpen freehand w/o any edge guide. At the microscopic level all edges are flat but a smoother transition to the secondary bevel is aerodynamically superior as there is less drag.
 
In theory, there may be a difference. In practice, it doesn't matter. All the "convex edge" stuff is a fad. Sharp is sharp.
 
Bill DeShivs said:
In theory, there may be a difference. In practice, it doesn't matter. All the "convex edge" stuff is a fad. Sharp is sharp.
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Try cutting through cheese and you would notice a significant difference in the force required for the blade to tranverse through the cheese between convex and flat at the same edge angle. I've tried it.
 
It's because most convex edges that are discussed, are zero edged. That makes them sharper than beveled. It's not so much the convex, but the zero.
 
It does seem very faddish. People also think that using the mouse pad sandpaper technique frees them from having to learn to sharpen. The only convex edges I've handled that would even come close to what I consider sharp have been done by professionals with power equipment. If anything sharpening with a mouse pad is harder since you have two variables to consider - angle and pressure. One or two strokes with a little too more pressure and oops there goes the edge :rolleyes:
 
Then people should always convex sharpen their cheese knives and hatchets.
 
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cotdt said:
Try cutting through cheese and you would notice a significant difference in the force required for the blade to tranverse through the cheese between convex and flat at the same edge angle. I've tried it.
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My family would prefer I not cut the cheese.

Never tried a convex edge since I have always found that a conventional edge does everything I want it to do.
 
theonew said:
It does seem very faddish. People also think that using the mouse pad sandpaper technique frees them from having to learn to sharpen. The only convex edges I've handled that would even come close to what I consider sharp have been done by professionals with power equipment. If anything sharpening with a mouse pad is harder since you have two variables to consider - angle and pressure. One or two strokes with a little too more pressure and oops there goes the edge :rolleyes:
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Actually convex edges have been used since before the invention of steel, it's definitely not a fad. Look at the appleseed shape of the Japanese katana, or an axe. Actually nearly all vintage knives used convex.

The sandpaper/mousepad technique seems super forgiving to me. Unless you suddenly decide to hold your knife at some nearly perpendicular angle, you're not going to ruin your edge. You get good tactile feedback so you know when the angle is exactly right, it makes a specific sound as well. It's probably the fastest non-power-tool sharpening technique there is, you can go from a full reprofile to a mirror polish in 30 minutes.
 
cotdt said:
Actually convex edges have been used since before the invention of steel, it's definitely not a fad. Look at the appleseed shape of the Japanese katana, or an axe. Actually nearly all vintage knives used convex.
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So it's a retro fad then ;)

cotdt said:
The sandpaper/mousepad technique seems super forgiving to me. Unless you suddenly decide to hold your knife at some nearly perpendicular angle, you're not going to ruin your edge. You get good tactile feedback so you know when the angle is exactly right, it makes a specific sound as well. It's probably the fastest non-power-tool sharpening technique there is, you can go from a full reprofile to a mirror polish in 30 minutes.
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What exactly makes it more forgiving and at the same time faster? All of the "features" you describe like tactile feedback and sound seem to be much more amplified to me when using a stone.
 
Anyone that has doubts about a convexed edge needs to handle one of Kiku's blades or a Rockstead.
 
samhain73 said:
It's because most convex edges that are discussed, are zero edged. That makes them sharper than beveled. It's not so much the convex, but the zero.
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well said. :thumbup: the convex (IMO) adds strength as a full zero is very thin...I find my convexed edges to be very durable. :)
 
I can't do a convexed edge on a stone properly. I can do a v-edge on a stone.
 
theonew said:
What exactly makes it more forgiving and at the same time faster? All of the "features" you describe like tactile feedback and sound seem to be much more amplified to me when using a stone.
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A stone does give more feedback but it is also far more expensive than sandpaper.

With a stone, you are making smaller contact area with the abrasive. With the sandpaper/mousepad, you get more contact area such that you can use a little pressure (just a little) and get faster results. The grind marks are also smoother and it's easy to get a mirror polish. Here's a Fallkniven VG-10 knife that I just did with sandpaper/mousepad in 10 minutes, to hair-whittling sharp.

convexwm1.jpg
 
cotdt said:
With a stone, you are making smaller contact area with the abrasive. With the sandpaper/mousepad, you get more contact area such that you can use a little pressure (just a little) and get faster results.
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You have more of a contact area because you are sharpening more of the blade, how is that faster? Also how do you regulate the pressure involved? If your pressure fluctuates you'll be sharpening the very edge at different angles, which will either A. add time or B. result in a dull edge. With a flat stone, pressure doesn't matter nearly as much. Also you are still not free from having to maintain a consistent angle, lift the spine a little and increase the downward force by a minute amount and you've effectively sanded down the edge :eek: You may have mastered this technique I just don't see how it is easier than just free hand sharpening on a flat stone.
 
theonew said:
You have more of a contact area because you are sharpening more of the blade, how is that faster? Also how do you regulate the pressure involved? If your pressure fluctuates you'll be sharpening the very edge at different angles, which will either A. add time or B. result in a dull edge. With a flat stone, pressure doesn't matter nearly as much. Also you are still not free from having to maintain a consistent angle, lift the spine a little and increase the downward force by a minute amount and you've effectively sanded down the edge :eek: You may have mastered this technique I just don't see how it is easier than just free hand sharpening on a flat stone.
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Yeah you still need consistent pressure and angle with sandpaper/mousepad, but to a newbie, as long as your angle is somewhat close you're still sharpening the edge. With a stone, a newbie might be using the wrong grit stone, like a polishing stone for reprofiling, and never get anywhere because the stone's not touching the edge. She would wonder why it is not working. With sandpaper/mousepad, even if you jump from coarse to ultra fine grit, at least you're still getting the edge. It's much more newbie friendly.
 
cotdt said:
Yeah you still need consistent pressure and angle with sandpaper/mousepad, but to a newbie, as long as your angle is somewhat close you're still sharpening the edge. With a stone, a newbie might be using the wrong grit stone, like a polishing stone for reprofiling, and never get anywhere because the stone's not touching the edge. She would wonder why it is not working. With sandpaper/mousepad, even if you jump from coarse to ultra fine grit, at least you're still getting the edge. It's much more newbie friendly.
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Or the newbie is sitting there for a million hours getting the edge slightly sharper and then dulling it again. I don't know, just seems like a sloppy way to learn how to sharpen. This is my last post on this, sorry for the drift hardheart :o
 
theonew said:
I don't know, just seems like a sloppy way to learn how to sharpen.
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The alternative is investing a fortune in a set of Shapton stones (or some equivalent). The sandpaper/mousepad is much cheaper and works just the same (with its pros and cons of course).

Back on topic. What other methods, other than these two, can make convex edges? It seems that with sharpening systems, you would have to settle for a microbevel as an inferior alternative to a convex edge.
 
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