Why is Convex bad?

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d.weglarz13

Joined
Jun 4, 2008
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Hey guys. I hear so much on here debating Convex vs Vgrind. Well, my questions are:
Why would someone want a V grind instead of convex? some say V is better?
I know its talked about a lot, but why would convex be better?
And, what do you guys prefer on what type of knives? (style and size)
I am most interested in utility, tactical, camping, combat kinds of knives. What kinds of grinds are best for what kind of slicing/chopping, etc.
Like I said, i know there are many mixed feelings, so please express any and all feelings. Thanks for the info.
 
Convex is just fine, so are V grinds, I prefer V grinds, though if I get a belt grinder I may warm up to convexing a bit more.
 
d.weglarz13 said:
Please tell WHY you would choose one or the other. Thanks
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Flat grind is easier to sharpen, and there isn't a real performance difference. It depend on what you want to do with it. An axe, for example, is best suited with a convex grind.
 
Keep in mind that convex edges and convex ground blades are different. The only reason I use convex edges is because that's what I get off the belt sander I use to sharpen. Recently, I've even went to sanding over the platen, so even this reason is gone, except for machetes.

The only knife I've used with a convex primary grind cut poorly compared to a flat ground blade from the same stock. It was a full convex grind, all the way to the edge. It was very strong, and very sharp, but it cut worse than my other knives. Full convex grinds have an advantage in chopping knives as this grind reduces binding when chopping wood or similar material.

Its all about cross section geometry. A flat ground blade with the same edge angle at the V-edge will fit inside a convex ground cross section of the same width and thickness. Then a thinner convex could fit inside that, and so on. It all depends on who grinds it and how thin they are willing/capable of going. Friction plays a part, but its not like V-edges can't be polished too.

Edited to add: I do like the look of a full convex grind better than flat grinds, but that is a cosmetic issue. I suppose its time to do a real test and see what I find.
 
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This is a subject that I see as 20% science and 80% personal experience. First, I think it is very safe to say that convex edges are not at all ""bad", unless your definition of "bad" is that most production knives do not arrive with them. IMO, it is just the opposite. I'm not deep enough into the science of edge geometry to say whether one grind such as convex is superior to another. I can say that it seems that convex holds an edge longer than V grinds - on my knives, and what I use them for in the outdoors. I can get them sharp enough to sail through phonebook paper without a tear and that's both as good as I can get my V grinds and good enough for me. I also find them easier to sharpen in the field using a piece of sandpaper versus a sharpener. Add to that the convenience and efficiency of using a belt grinder to sharpen at home, and the result is most of my knives are convex. Your own results and preferences may vary.
 
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Ill go with a regular V-ground edge because its easier to sharpen, and im still practicing my freehand convex sharpening skills.

I found no real difference between the 2 edges when cutting up firewood, sharpening sticks and regular camp chores, my V-edge was just as good as the convex. My girlfriend seems to prefer my convexed F1 in the kitchen though, but i suspect its only because it came scary sharp from the factory.
 
A convex is just a V-grind with the bevel shoulders smoothed away. Slicker cutting.

Bevel shoulders are the devil. They just get in the way.
 
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d.weglarz13, I think the real question is: why do you think convex is bad?

I haven't tested convex grinds enough to form a definite answer, but what I'm seeing so far is that they are very good cutters. Most of my high-end knives are 20° v-ground bevels; most of them are flat ground, but some are saber ground but with a 15° edge, one is hollow-ground and so on. Then I've got a bunch of scandis. Now, this is where the testing should begin, because nothing cuts like a scandi when it comes to carving and whittling. But, I'm really impressed by convex ground blades of equivalent dimensions to my scandis. They cut really well — and they hold an edge better than most scandis. It's all about angles and yes, you can get a scandi grind that won't roll over, but with the convex that doesn't seem to be a concern. I'm getting into convex blades and I'm diggin' what I'm seeing so far. They are different to sharpen, but that doesn't mean that they are more difficult. I've never had a problem sharpening v-grinds, yet I see thread after thread with questions on how to do it. Regardless of the grind — it just takes practice.
 
As long as a blade is thin enough to cut what you want cut with ease and thick enough to resist being damaged by what you're cutting and how you're cutting it is all that matters. Convex, concave, flat, whatever.
 
Convex or flat really is dependant on the method you use to sharpen. You can make either one cut better or make them stronger. You want your flat V edge to cut better or slice better? Thin it out or put a more polished or coarser edge on it. You want to do the same with a convex edge? Do the same thing as you would for a flat v edge. You want either one to be stronger? Put a thickeredge on both. Witch style is better? The one that is easiest tfor you to sharpen and maintain. For me that is a convex edge, and for many other people it is a flat V edge.
 
thombrogan said:
As long as a blade is thin enough to cut what you want cut with ease and thick enough to resist being damaged by what you're cutting and how you're cutting it is all that matters. Convex, concave, flat, whatever.
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There's your answer.
 
Ok, cool. To answer your question Stoffi, I hear so much about how guys with contraptions like the Edge Pro love their V grinds, and personally i think they look great with that mirror finish you can get from a perfect angle like those guide systems offer. I don't have any of those but i did just invest in a couple of DMT 8" bench stones, and 2 Shaptons, based on the mindset that freehand is the best way to go. And, to me it is. I love to bring my knives sharp on those, now that i have practiced a lot. But, they just never look as nice as those who use the systems(or maybe those with years of skill). I have on Barkie with a convex, and it seems sharper than anything, but I guess I am trying to figure out more about these convex edges, although i am still a little foggy on the different types of convex that you guys describe and for what they excel at. I personally want the best edge for cutting paper, be able to hack off a limb(i know, only 6" but what the heck) and even use for a lot of camping chores including batoning. so, i don't know if any of this blabbering helps, but thats what I am thinking. So, thanks for all the replies, and more welcome if you like.
Dave
 
That blackjack link is just chock full of inaccuracies. "Big" carbides in a steel like ingot D2 are what, 20 some odd microns? Show me a cross section comparison between v-ground and convex at that level where there is 4 times more steel supporting the carbides. After that, I would like to see convex edges providing 4 times the support to sub-micron carbides in 52100 or 12C27.
 
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