Convex Edge Better by What % ?

A

allout

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Mar 27, 2008
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I am not good friends with math but I know some people are. I have no doubt that convex is better but I wonder by how much. I would think it is better than 3% and less than 30%. Is this not a form of terminal ballistics which would mean the % gain of a convex edge is calculable?


OR


Is it Magic ? :eek:
 
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:) 99.97% sure that pi (3.14159..) involves because of the convex curvature/arc. Yeah it goes something like: sqrt(2*pi*t)*((t/e)^t) or roughly around 17.357% improvement on Tuesday.

Seriously, many answers would depend on blade+edge geometry, steel + ht, fracturing interactions, etc..
 
bluntcut is right. Convex is a complex proposition. Thin blade stock or thick(er) and by how much? How high is the convexing -- full grind or edge bevel? On a flat grind or hollow grind? Chris Reeve puts a convex edge bevel on a hollow ground blade.
 
One isn't "better" than the other. Just like different steels, they have unique characteristics that suit every person differently. It's a game, you have to play with many knives to figure out what works best for you. Convex vs. V edges both perform differently: one has the potential to hold an edge longer and one can get much sharper providing better slicing capabilities.

I personally like V edges because they aren't a pain to sharpen. CRK recommends you strop your knives to maintain sharpness, but I don't have time to strop the knife I carry every day. By the end of the week, my blades usually need a little touch up with some coarse rods, and with my sharpening setup I wouldn't be able to re-profile a convex edge.
 
What bluntcut said, but I think he forgot 6^7** (-.2) and carry the 2. Seriously, in theory there may be more steel behind the edge than a traditional V grind, but it would be difficult to compare in real life. As he notes, other factors would affect the outcome (if any). (Written by a math phobic:o.)
 
JustinWatts said:
I personally like V edges because they aren't a pain to sharpen. CRK recommends you strop your knives to maintain sharpness, but I don't have time to strop the knife I carry every day. By the end of the week, my blades usually need a little touch up with some coarse rods, and with my sharpening setup I wouldn't be able to re-profile a convex edge.
Click to expand...

I resharpened the convex edges on my Sebenzas freehand. Like the difference between convex and V, it's usually a matter of personal style and experience.
 
Ok, so assuming the knife is the same, assuming the location of the edge shoulder and the very apex are the same, and the only variance is the convexity of the edge, you can quickly calculate the additional material behind the edge on each side.

You can decide the radius of curvature, and if you take the length from the apex to the shoulder, these calculations should contain everything you need to find the additional material behind the edge.

Convex_Edge_Calculation.jpg


The area calculation is the area of the whole piece of pizza, minus the area of the triangle, leaving you with the additional area (the convex crust!)

Now, how much does that change in material change cutting performance? I have absolutely no idea :D
 
I have been told in my post below about my Outcast, and have read several times here and other places that “it will chop much better with a convex”. I do think this is true. I am curious if any math has be done that can be translated into English, preferable something on about a 6th grade level. Like Prof. Kaku said, I’m paraphrasing, “even the most advanced scientific concepts should be explainable to a grade school kid if the concepts are truly understood”


With stuff like constants and points of reference is it not possible to show examples? Or, what some believe to be expletives in mathematics, a “ball park” figure? Mathematical approximates to achieve “useable math”. In the 80s we had a book called something like “Military Wounds and Terminal Ballistics". Though the book was thick with all sorts of equations it was able to filter the results for the layman to use as a reference and allow useful comparisons.
 
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There are too many variables to make a blanket statement, on the value of a convex edge. There are some knives I like with and some not. If your working with a very thin blade stock and are using the blade for slicing, applying a convex edge is not useful to the cutting ability of the knife. On the other hand if it's a hard use blade a convex edge is quite valuable.
The reason I prefer a V edge over the convex style is its ability to be re-sharpened by someone other than the original user. The V edge is done at a set angle where the convex is hit or miss with the person sharpening having to interpret the pressure used, the angle of approach while trying to keep the cutting edge in the center of the blade. I've put hollow ground edges on convex ground bevels and they do cut well; but its a contradiction of purpose.
 
Maybe it is time to call in the professionals, maybe it time to call the Mythbusters.

Anyone have that number?

KifeVsGun.png











Did you know that the word Myth comes from the ancient greek language and it means “a situation devoid of math”?:rolleyes:
source - http://tinyurl.com/of56rhm
 
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The vast, vast majority of sharpening of metal knives has been free-hand - producing convex edges. Somehow, that was not a problem.
 
Wouldn't the material being cut also matter? Performance wise, a serrated edge bites/slices/cuts into fibrous materials much better than a non SE knife... So I guess the answer is...wait for it (pulls out calculator and calculates furiously)... 42.
 
Welli think it's more science Than math. A round smooth surface will push material out of the way during a cut and add a "pulling apart the two pieces" effect. Like when you hold a rag taught to cut right through it versus trying to cut it all limp. Also less surface area contacts the material reducing friction. I find a mirror polished convex also bites deeper because of the ultra refined edge.

This is why my machetes have super wide polished convex edges and my pocket knives have either shallow minor convex or almost v grinds.

Trying to add math is impossible due to the variables. I can almost guarantee you couldn't cut the exact depth with the same blade twice on the same tree so trying to add numbers to every knife ever just won't work.

Convex the hell out if that blade and see if it cuts better for you. Then decide " how much better" you like it.
 
Chopping is straight push cutting as well so polished edges excel at that vs toothed edges excel at draw cuts. Forgot to mention that.

If you are any where near Connecticut I'll convex your blade for free if you let me play with it before and after.
 
Operating under the assumption that convex is superior is a joke, I hope. Neither style is better, it's printed letters and cursive letters, one mans print may be as hard to read as anothers cursive. What matters is the burr free apex, not which way you get there.
 
allout said:
Mr. Linton, would you explain more on your line of thought?
Click to expand...

If you free-hand sharpen, minor variations in angle produce a convex edge.

I have examine many old knives, including several used by top professional wood carvers. All had convex edges. (Not a "scandi" to be found.)

I free-hand sharpen. My knives cut just fine.

As a result, I conclude that convex edges work and that perfection, or near-perfection, in creating an edge has no practical utility.

YMMV
 
Many variables does not render math useless - Does it?

Math did get us to Mars:saturn:
 
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