Convex edges: Are they really practical?

[Lapedog]

How, exactly, would it be more difficult to hit the apex on a convex? Any angle of approach less than that of a V edge will result in the wear being born directly by the edge shoulder. Please explain your reasoning.

When I buy a new CRK with its covex edge I find it difficult to hit the apex because the way I find my angle is laying the blade flat against the stone and raising the spine until I feel it go over the shoulder of the edge. With a v edge when I go over the shoulder I am hitting the apex. (Or close, because I freehand it is not a perfect V)

When I get that new CRK and I am having trouble sharpening it I take it to my local sharpener. He does freehand on Japanese waterstones and gets a great edge. Again not a true V but close enough that upon being returned to me sharpening is no longer a problem.

 

[FortyTwoBlades]

When I buy a new CRK with its covex edge I find it difficult to hit the apex because the way I find my angle is laying the blade flat against the stone and raising the spine until I feel it go over the shoulder of the edge. With a v edge when I go over the shoulder I am hitting the apex. (Or close, because I freehand it is not a perfect V)

When I get that new CRK and I am having trouble sharpening it I take it to my local sharpener. He does freehand on Japanese waterstones and gets a great edge. Again not a true V but close enough that upon being returned to me sharpening is no longer a problem.

Instead of doing it by feel, try doing it by sight. Raise the spine until you see the edge contact the stone.

 

[Pilsner]

When I buy a new CRK with its covex edge I find it difficult to hit the apex because the way I find my angle is laying the blade flat against the stone and raising the spine until I feel it go over the shoulder of the edge. With a v edge when I go over the shoulder I am hitting the apex. (Or close, because I freehand it is not a perfect V)

When I get that new CRK and I am having trouble sharpening it I take it to my local sharpener. He does freehand on Japanese waterstones and gets a great edge. Again not a true V but close enough that upon being returned to me sharpening is no longer a problem.

I know that it’s blasphemy to say such a thing round here, but a *whispers* Work Sharp will always give a convexed edge, as it is in the nature of belt sharpeners. Course it isn’t practical in the wild, but still...

Nothing to see here, move along.

 

[Sergeua]

Here is a picture demonstrating the variations of a convex edge i can see happening.

Let's examine the red and the black.
This is the only scenario I see of a convex and "V" having same apex angle. The convex edge in this case has an advantage over the V as it doesn't have the shoulders and it's a better cutting geometry. To hit the apex the angle to the abrasive will have to be the same between the two as demonstrated by the yellow line. As FortyTwoBlades said when you make a mistake and go shallow while sharpening you are not going to touch the shoulder ( of black ) and will be closer to the apex of the convex (red) eventually having higher chance to abraid down to the apex. Hence the ease of maintenance. Voila! It is true in this case.
However, we compared a primary ground convex geometry to a flat ground one with a secondary grind V edge of same angle. It should really be compared to a zero grind to be fare. Zero grind is not pictured above, but it can be imagined as a straight triangle connecting the three points and it's going to reside inside the above diagram.
I say it's just as easy to stay off the shoulder while sharpening V and by doing this you will be hitting the apex.

When we compare apples to apples answers are more obvious. Convex grind in this example is ofcourse stronger and it's one of its key benefits.

So again compare first two pictures from the new picture exhibit^ presented. That's why i said it's easier to get to an apex of "V" vs a "U" without degrading performance while at it.

Now take something like sebenza we see a convexed secondary angle that is like the blue or green in the first picture. In terms of this thread, in sebenza example, I don't think it's practical. It cuts poorly and the strength is not really an issue. The (green from first picture) edge is what happens as a result of overstropping or various sharpening abilities and perhaps we can agree it is not ideal. It gets progressively harder to get to the apex with future sharpening and performance keeps on degrading.
This is probably the case of why people here state their V (black triangle) is better at holding the edge over convexed (green) edge. V is simply sharper geometry wise.
I'm not an expert, I'm not afraid to be mistaken so #correctmeifimwrong.
I don't believe we are overthinking things in this thread. I think it's good to get your theory straight so you have a clear understanding of what you are doing while sharpening.
Some of you here just blurred the line between convex and free hand sharpened V.
Its two different things, with different ideology behind it. When a skilled freehand sharpener puts these out, the two are easily discernable. This post almost feels like whatever mickeymouse stuff you do on your edge will just produce a good convex.
Its easier for manufacturer to produce a V for a reason. #geometrymatters M marcinek

 

[marcinek]

I know that it’s blasphemy to say such a thing round here, but a *whispers* Work Sharp will always give a convexed edge, as it is in the nature of belt sharpeners. Course it isn’t practical in the wild, but still...

Nothing to see here, move along.

"...the nature of belt sharpeners without a platen."

But yes, a slack belt will convex the blade. It's what BRK, for example, uses to convex a section of flat ground blade.

 

[marcinek]

Its easier for manufacturer to produce a V for a reason. #geometrymatters M marcinek

And the reason is is that they do not create the edge freehand.

Unless one can maintain the exact same angle while freehand sharpening (and you cant), you are creating a series of microbevels and convexing.

 

[Pilsner]

"...the nature of belt sharpeners without a platen."

But yes, a slack belt will convex the blade. It's what BRK, for example, uses to convex a section of flat ground blade.

Quite right, mea culpa.

 

[FortyTwoBlades]

Here is a picture demonstrating the variations of a convex edge i can see happening.

Let's examine the red and the black.
This is the only scenario I see of a convex and "V" having same apex angle. The convex edge in this case has an advantage over the V as it doesn't have the shoulders and it's a better cutting geometry. To hit the apex the angle to the abrasive will have to be the same between the two as demonstrated by the yellow line. As FortyTwoBlades said when you make a mistake and go shallow while sharpening you are not going to touch the shoulder ( of black ) and will be closer to the apex of the convex (red) eventually having higher chance to abraid down to the apex. Hence the ease of maintenance. Voila! It is true in this case.
However, we compared a primary ground convex geometry to a flat ground one with a secondary grind V edge of same angle. It should really be compared to a zero grind to be fare. Zero grind is not pictured above, but it can be imagined as a straight triangle connecting the three points and it's going to reside inside the above diagram.
I say it's just as easy to stay off the shoulder while sharpening V and by doing this you will be hitting the apex.

When we compare apples to apples answers are more obvious. Convex grind in this example is ofcourse stronger and it's one of its key benefits.

So again compare first two pictures from the new picture exhibit^ presented. That's why i said it's easier to get to an apex of "V" vs a "U" without degrading performance while at it.

Now take something like sebenza we see a convexed secondary angle that is like the blue or green in the first picture. In terms of this thread, in sebenza example, I don't think it's practical. It cuts poorly and the strength is not really an issue. The (green from first picture) edge is what happens as a result of overstropping or various sharpening abilities and perhaps we can agree it is not ideal. It gets progressively harder to get to the apex with future sharpening and performance keeps on degrading.
This is probably the case of why people here state their V (black triangle) is better at holding the edge over convexed (green) edge. V is simply sharper geometry wise.
I'm not an expert, I'm not afraid to be mistaken so #correctmeifimwrong.
I don't believe we are overthinking things in this thread. I think it's good to get your theory straight so you have a clear understanding of what you are doing while sharpening.
Some of you here just blurred the line between convex and free hand sharpened V.
Its two different things, with different ideology behind it. When a skilled freehand sharpener puts these out, the two are easily discernable. This post almost feels like whatever mickeymouse stuff you do on your edge will just produce a good convex.
Its easier for manufacturer to produce a V for a reason. #geometrymatters M marcinek

For purposes of convex-vs-flat comparison it is absolutely vital that edge angle be held constant. Which means that a convex will always fit within a flat ground edge of equal angle, and have a greater visual bevel width. Otherwise you could simply increase strength by increasing the angle of a flat-ground edge, too, and have more material at the shoulder again.

 

[marcinek]

Quite right, mea culpa.

Just being pedantic. And too much time talking with Mike Stewart way back when.

 

[marrenmiller]

You guys do realize that you're doing what always happens in a convex thread, which is arguing past each other about how you define a convex bevel. Either you round off the shoulders or you round off the apex. Who's right in this scenario depends on which definition you're talking about, as per usual.

And there seems to be examples of both kinds of convex blades being used.

 

[FortyTwoBlades]

You guys do realize that you're doing what always happens in a convex thread, which is arguing past each other about how you define a convex bevel. Either you round off the shoulders or you round off the apex. Who's right in this scenario depends on which definition you're talking about, as per usual.

And there seems to be examples of both kinds of convex blades being used.

The big issue there is that if you round off the apex you're just increasing the edge angle, which can be done with a flat grind, and then that flat grind is still thicker than a convex of the new increased edge angle.

 

[marcinek]

Either you round off the shoulders or you round off the apex.

Nope. What you don't realize is that when you round the apex off an edge, you dull it. That is what dulling is.

Convex edges do not have a rounded apex.

 

[Pilsner]

Either you round off the shoulders or you round off the apex. Who's right in this scenario depends on which definition you're talking about, as per usual.

And there seems to be examples of both kinds of convex blades being used.

Eh? Or just use some fine motor skills and sharpen the bloody convex. Honestly, I have a mental image of an infinite line of glazed, semi-robotic automatons, only capable of moving on a straight plane, disregarding human anatomy - blessed as it is with movements that describe natural curves.

Hey ho.

 

[Lapedog]

I know that it’s blasphemy to say such a thing round here, but a *whispers* Work Sharp will always give a convexed edge, as it is in the nature of belt sharpeners. Course it isn’t practical in the wild, but still...

Nothing to see here, move along.

I don’t use a work sharp though.

 

[Pilsner]

I don’t use a work sharp though.

But you could though.

 

[Lapedog]

But you could though.

Probably should. I’m a total novice when it comes to freehand sharpening anyway. Basically i can maintain an already decent edge.

 

[marcinek]

Probably should. I’m a total novice when it comes to freehand sharpening anyway. Basically i can maintain an already decent edge.

Or just get some wet/dry sandpaper grits and some cardboard. And you can convex away.

 

[Lapedog]

Or just get some wet/dry sandpaper grits and some cardboard. And you can convex away.

Maybe it’s about time I do that. What sandpaper would you recommend for coarse, med and fine.

 

[Pilsner]

Probably should. I’m a total novice when it comes to freehand sharpening anyway. Basically i can maintain an already decent edge.

I reckon that is the point, so no need to change. I’m a big fan of maintaining a good edge, rather than letting it go to pot in the first place.

I bought a WS in order to put a convex edge on a BK2, and other similarly silly FB knives. It was merely a labour saving device, but it is actually very good indeed. Just watch out for the tip!

 

[FortyTwoBlades]

Is your knife sharp? Good. Is it dull? Make it sharp. Is it getting routinely damaged cutting things you want it to cut? Thicken it up. Is it not cutting as well as it should be even though it's sharp? Thin it out.