Convex edge pros and cons

A

AndrewtheHoosier

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Aug 25, 2016
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So I've heard a lot of talk about people liking convex edge grinds on their knives and some people couldn't be more against the idea. From what I've heard convex edges are supposed to have greater edge stability and toughness, but don't slice as well. If that's true, would it be a good idea to put convex edges on more chip-prone steels? For example I have a s110v pm2, and since s110v has a higher carbide content it can tend to be a little chippy, so would I benefit more from putting a convex edge on it? Any input appreciated.
 
What you heard is the opposite of the truth actually. Completely backward. They slice better, but have less stability when compared to a V grind with the same angle at the apex.

The convex grind apexes at a certain angle and then the angle gets more acute as you travel back. Whereas a V grind is the same all the way back so you actually have more steel behind the edge. This results in a more stable edge, but poorer slicing.

The angles themselves matter more than the grind when determining how an edge will perform. The real pros and cons for convex and V grind come down to how they're achieved. I think a convex grind is a little more forgiving when it comes to a free hand technique.
 
I know TLE Sharp is a pro but some of the things you said in the above ppst are difficult to understand. How could a V shaped edge has more steel behind the edge than a convex edge? My understanding of the pros and cons was basically what the OP said, which of course could be wrong.
 
sharp_edge said:
I know TLE Sharp is a pro but some of the things you said in the above ppst are difficult to understand. How could a V shaped edge has more steel behind the edge than a convex edge? My understanding of the pros and cons was basically what the OP said, which of course could be wrong.
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Basically imagine a convex as a V with the bevel shoulder rounded off. Edge angle must be held constant for a valid comparison, and when you do so a convex has less metal in the "cheeks" of the bevel.
 
profiles.gif

This illustrates my point pretty well. They're both the exact same angle at the apex.

It's a bit exaggerated here, but you can see how the convex would drop away from the apex angle, where the V edge has more steel behind the edge, maintaining a consistent angle.

Why whomever made this decided to give the V illustration much thicker stock is beyond me.
 
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The problem in understanding lies I think with the way you accomplish the convex.

If you hold the blade at 15 degrees while sharpening for a convex edge you do in fact have more steel behind the edge than you would on a 15dps V grind, but only because you're actually getting something closer to 25dps at the apex and 15dps at the shoulder.

In an accurate comparison though, where the apex angle is the same, a V edge will have more steel behind the edge and a convex edge will slice better due to the narrower shoulder causing less drag.
 
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In use, once the difference between the primary and cutting grind angles on a V edge drops down to only a few degree, the performance differences diminish greatly and you would be hard pressed to tell by feel.

As the difference between primary and cutting angle increases, converting to a convex will yield greater and greater benefit. Generally speaking, they are at their best with chopping tools, tho work well for EDU.
 
So how would a 40 degree inclusive straight edge compare to a 50 degree inclusive convex edge (just an example)? Is there a way to get the same stability out of a convex edge, while remaining equal or better slicing?
 
Flat mostly aids in resisting torque. Otherwise a convex will be pretty much the same though with better slicing ability.
 
AndrewtheHoosier said:
So how would a 40 degree inclusive straight edge compare to a 50 degree inclusive convex edge (just an example)? Is there a way to get the same stability out of a convex edge, while remaining equal or better slicing?
Click to expand...

It comes down to meat behind the edge. If you had a relatively thick primary grind and an inclusive of 40°, grinding the shoulders off will make a big difference in cutting ability and the edge won't miss the reduced stability. As the edge gets thinner overall the convex brings less to the table though still performs great. Most primary grinds are so overdone unless you are using the knife as a prybar you will never miss the steel that was removed.

As with thinned V bevels, until you get down to sub 25° the lateral stability should hold up pretty well. Thin is sharp, but not without limits, in my experience right about 23° and less on thin stock, and the lateral stability on most "budget" steels takes a notable drop - it doesn't matter what type of grind it has.

If you took two relatively thin primary grinds and convexed one to 40° and the other to a V bevel at 30° the V bevel will cut better. As you increase the stock thickness, there will come a point where the more broad convex begins to outperform the V bevel on some materials as it has less wedging behind the edge - that is going to relative extremes though.
 
AndrewtheHoosier said:
So how would a 40 degree inclusive straight edge compare to a 50 degree inclusive convex edge (just an example)? Is there a way to get the same stability out of a convex edge, while remaining equal or better slicing?
Click to expand...
Too many variables to say really. Material being cut, primary grind on the blade, stock thickness, thickness behind the edge all come into play.

As a general rule, as stated above, thicker blades meant for chopping, batoning, etc. will benefit more from a convex edge than a thin blade will.

All of my axes and my Cold Steel SRK have a convex edge, but I'd never bother with one on a Sebenza 21.
 
I'm not going to opine here because my views will simply create controversy. Let me just say that, if you have comparable angles at the edge, both will cut about the same. I didn't say exactly the same. What happens above the edge has more to do with friction reduction than profile. I'm just suggesting that the differences are not very important. Flat sided bevels are certainly easier to maintain.
 
Thickness behind the edge and thickness of stock play major role here,and they are best for axes and choppers,although all hand sharpened edges are slightly convex.my favorite is slight almost flat convex grind,most convex knives on market that are factory made have obtuse Axe like convex grinds Lol.So what matters most is thickness behind edge,stock thickness,edge angle,and primary grind,as not every material being cut is same
 
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