Convex edges are the best!

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FWIW - I assume that a human hand, no matter how skilled, can not hold a constant fixed angle when hand sharpening on a stone. This would obviously mean that a slight rocking motion occurs which will round the edge bevel. We could call this rounded bevel "convex" as it wouldn't be either flat nor hollow. It may consist of layers of stepped flats that are blended together but it's closer to convex than any other edge type I'm aware of.

Please, anyone wanting to learn something from this discussion, remove the "science" from your mind and leave the common sense behind. ;)


--Dave--
 
In my mind…
When I bought a knife, any knife, I like to know the knifes performance. The producer of the knife have give the knife a ultimate sharpening angle, the best sharpening angle for just this knife, the steel quality and so on.

To have a possibility to learn to know the knife, I must use the knife a lot to find out how it performs. When I use it, it starts to get dull. When it gets dull, its performance changes a little.

So, I sharpen the knife in the exact same sharpening angle and continue work with the knife, still trying to learn its performance. This take some time for me to do, and I must sharpen the knife some times during this “test”.

After some time, I have learn how the knife performs. The knife do things I like it to do (not what the knife like to do). When I know its performance, I can start to change the sharpening angle on this knife so it fits better what I like to use the knife to do. Sometimes big changes, some times very small changes of the edge.

The main thing is that I first need to know the knife, after that, I can change it, if it needs to be changed.

When I sharpen a knife by hand, I also change its performance because I can not perfectly hold the sharpening angle there is on the knife. That also means that I have no possibility to learn its performance because the edge on the knife change a little every time I sharpen it by hand.

For some this can seams like precision thinking, and yes, it is. Some work I do with my knifes needs this. In that case, I am a perfectionist. In other cases, I do not really care so much if the edge have 22 or 24 degree sharpening angle – or if the edge is perfectly straight - or slightly convex.

The main thing is, I like that the knife shall do exactly what I like it to do, every time I do it. To reach this, I first need to know the knife and how it performs. When I know this, I can also change the edge (and the performance) so its fits my needs.

To change a knife before I know how it perform seams to me a little odd because if I do not know how it perform, why change it?

Sometimes when I meet people and we talk knifes, I have notice that there is not so many people that really know their knifes. They just use them, sharpen them, resharpen them, grind them, call them names and ask me why the knife do not work as they like it to work. My answer is the same, you must first learn to know your knife, and then you can change it. When you, after this change, find that you like the knife, hold that edge in exactly the same sharpening angle – and your knife performs as you like it to perform.

When I am in the perfectionist mode and talk to a man who is not, there can be some conflicts between us because we use the same words – but we have different meanings of the words we use. That can be fun - if we both are in the humorist mode. If not, it can be a hard discussion before we find out what we are argue about.

If a edge is straight, then it is straight for me, absolutely flat (perfectionist mode).
If the edge is convex, then it is convex. If it is convex 0,25 degree or 25 degree = convex. It is not straight, (perfectionist mode).


Example (humorist mode)

You now, what is 1 ?
1 is something between 0,5 to 1,5.
So, 1+1 (0,5 + 0,5) = 1 (can be)…
And also 1+1 (1,5 + 1,5) = 3 (can be)…

Before we do the counting we must define the value of 1.
If 1 is really 1, it’s look like this 1 + 1 = 2 (can be)…

It is the same with straight and convex edges. Define the different types of edge.
Suggestion: if flat is flat, then everything who is not flat = convex or hollow on edges.

If flat is flat, then 0,25 degree convex is 0,5 convex – and 0,5 hollow is 0,5 hollow. If not (humorist mode) then I can change 0,5 convex edge just 0,5 degree down to a hollow edge…or?

It must be simpler to define what is flat (straight).

Thomas
 
Dave very clear and sensible post. Thanks I wish I had made it about 20 posts ago.

Thomas, I have nothing against people who need or want an edge as close to perfect as they can get it. I also think most sharpening systems are a great way to learn how to sharpen. It was very easy for me to learn to free hand sharpen after I learned how to get a sharp edge with the system I was using. I now sharpen by the method I describe in my first post in this thread, and am very happy with my results. I call it a convex edge because that is what it is. Some of the edges are more convex than others it depends on what I want on the knife.
 
these same types of information gathering ordeals happens quite often with rifle reloading! there seems to be a point where i run into" analysis perallasis "with to much info", or information which goes beyond my practical, utilitairian,zen like, sacred cow tipping,middle eye visions;and sometimes things im just to stupid to understand! i blame nobody,but im there now.
 
Donny just what do you need to be cleared up? If its anything about my method just ask and I'll try to explain it more.
Ooops, I see he is no longer with us. Never mind.
 
Cliff Stamp said:
Originally Posted by Saberman
I've never liked thinking that a convex edge as a neat evenly shaped curve, but as a parabola.
The actual defination just means above flat, it does not need to be circular, i.e., have a constant radius.

-Cliff
Click to expand...
Thank you for the definition.
 
I assume that a convex edge is better suited for larger blades. I wouldn't think the pros of convex would apply much to smaller blades. What benefits would a small (3-4" blade) knife receive- particularly a pocket knife?

Correct my thinking?
 
Jamesh Bond said:
Correct my thinking?
Click to expand...

It isn't as much about the curvature as the thickness, this is where people get really mislead into a bunch of hype and nonsense about some mystical properties of convex grinds. Most of the convex grinds people praise are actually just very thin and close to flat. THe actual utility of convex grinds on knife edges is to allow a slightly more obtuse angle at the very edge which is usually optimal. You can do the same thing with a micro-bevel and a more optimal dual v-grind is far more efficient than a convex bevel which isn't as optomized so again focus on the cross section first.

-Cliff
 
Jamesh, good question. Convex edges work as well as any others on small and large knives. For me they work the best, mainly because of the reasons given in post #1. You can make them as thick or as thin as you want depending on your needs. You can fully convex the blade or just the edge and or anything in between. I have convexed almost all my knives from very small pen slipjoint knives to large choppers. The convex edges are adjusted to the type of work/cutting they do. Most of my edc knives are 3 inches and under and are all convexed.

Okbohn, I know how you feel.
 
The most noticeable "performance boosts" I've gotten by applying a convex edge, were on large, stout blades. I kept the actual edge angle the same as I would have otherwise. I believe, but can't prove, that these blades have far less steel in contact with the material being cut,at any given time, than they did in conventional flat-ground state. They seem to hold their edge somewhat longer as well. It's frankly hard to say, because they were well-treated steel that held an edge just fine beforehand.

I find it makes a noticeable difference when chopping or splitting wood, and no difference at all when shaving hair.

Great googly moogly, I made my own head hurt...
 
Is this a trick question?

Where the edge meets the flat, it was rounded back to meet the flat of the blade. They bind less. They're not noticeably sharper, nor less sharp, because I used the existing edge as a starting point. For the first 1/32" or so, they're unchanged. No, I didn't examine them under an electron microscope or anything.
 
GibsonFan said:
Is this a trick question?

Where the edge meets the flat, it was rounded back to meet the flat of the blade. They bind less. They're not noticeably sharper, nor less sharp, because I used the existing edge as a starting point. For the first 1/32" or so, they're unchanged. No, I didn't examine them under an electron microscope or anything.
Click to expand...

It must be sharper but be a bit weaker with that extra bit of metal removed, or why do it?
 
Depends how you define sharpness, I guess. I think of it as the included angle right at the edge, and how finely its polished. You can gash yourself wide open with a clean 90degree angle. Cuttingness (?!?) improved because of the shape. As far as weakness, they definitely don't dull or wear or chip any more than they did before.

Is there an official glossary I need to look at somewhere? I get the feeling I'm not explaining myself very well.
 
I'm understanding you just fine.
You are thinning behind the edge an leaveing the edge angle itself at the same angle.
 
Also, because of the extra thinning behind the edge, you can get away with a more obtuse edge angle that is more durable, but perceptually cuts like a more acute angle.
Nice thread, db.
All this convex talk has sparked an interest in convex that I never had. I just convexed two knives yesterday for the first time. One was my CRKT Polkowski/Kasper Companion and the other was my friend's Cold Steel Voyager. Given the softer-than-advertised steel of the Companion, I am curious how its gonna perform!
 
Jamesh thanks. That was my intent to spark interest in convexed edges, blades, and or grinds. And also provide an easy and simple way to apply them yourself so you can try it and see if it works for you. Did you use my method or another method? Please report back on how you like them after you have used them for a while. Oddly enough a Cold Steel AUS 8 Voyager was one of the first knives I gave the convex treatment too. I promptly lost it right after. Hope you have better luck. :)
 
Those voyagers are a pain in the butt to sharpen cuz of the stud/narrow blade combo. The new ones have bigger, pointier studs that suck even more!

I used 220 and 1000 wetordry sandpaper on a cheapie 1/8 iinch thick mousepad, took off burrs with the fine side of a standard silicon oxide Norton, then stropped on loaded leather. We'll see if the super- soft Companion sees any benefits, and I have to wait to hear about the Voyager (vg-1, FYI) from my friend.

I actually hate him. He's had the knife for a year, sent it back cuz there was too much carbon in it (surface rust you could have LICKED off), and bought a stone, but never sharpens! I sharpened it convex for that very reason.
 
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