How sharp is too sharp?

G

GYMBOOEE

Joined
Apr 26, 2002
Messages
207
I once heard somewhere that the sharper a blade is, the weaker it is. That's because an exceptionally sharp blade is usually thinner, due to all the honing. How true?

Should I be concerned about the edge on one of my 15-inch AK's--which I have honed "razor sharp"--that it might be more brittle (and maybe chip, bend, or possibly crack) when I use it for chopping? Is it a good idea to reserve this particular blade for "self-defense" rather than as a "field chopper"?

Yes, I do know that a "paper thin" edge is obviously weaker, but I don't go quite that far. In case you're curious about what I use for sharpening, it's a variety, because I haven't settled on a favorite. I've used everything from stone, diamond, chef's steel, files, kitchen sharpeners ... whatever's available.

What do you recommend for sharpening? What do you NOT recommend?

Thanks guys!
 
Haven't done it yet but a convex edge is generally accepted to be the best way to go, seems to give the best of both worlds as far as sharpness and strength.
 
I can only think of one scenario where the knife can be "too sharp":

...when the blade is sharper than the individual using it. ;)

:D


Seriously, though the more important area of concern is the grind of the final bevel.

Convex = chopping, push cuts, carving
Flat = general purpose
Hollow = slicing, paring

Polished edge = push cuts
Coarse edge = slicing cuts


If I were to pick an all-around edge to cover as many purposes as possible, I'd pick a polished, flat grind - which is easy for most to sharpen.

If I were to pick the highest performance edge = convex, coarse/polished
 
Different blades have different final bevel angles depending on what you want to cut and how. This goes for planes, chisels, knives, saw teeth, etc. I don't want to pretend to talk about what's the right angle for what, but yes, a wider angle ought to be more rugged for chopping. It does not make that edge any less
sharp, though!

You can have a dull straight razor and a sharp axe. When properly sharped, neither would be particularly good for the other's job.

In non-convex blades, the edge is the intersection of two flat planes. Sharpness has to do with just how smooth and flat those planes are.

(Please accept my apologies for referring to the angle of a "bevel", which seems to imply that a edge other than convex is acceptable. There's probably way to translate, but I don't feel like trying right now.)
 
I have a 15" AK with a fairly thin flat grind. I've used it to chop wood a few times. I think it's OK to have this configuration on a 15" as you don't get the weight, torque and twisting that you get on impact with a 21" blade. Since no one has yelled at me with this theory, I'm thinking that it is sound.

Though if I used this blade for a lot of chopping I'd attempt something with a thicker edge. However this flat ground AK is good for a multitude of purposes.
 
Now that I've experienced a true convex edge on a khukuri I'm convinced that it is the proper shape for this type of blade.
 
Steel type and hardness play a role, along with edge geometry. That said, I have no idea what the ideal paramaters are for a khuk.

It also depends on what you chop - an edge that does fine in clear fresh wood could easily chip out if you hit a knot, piece of metal, funky swirl in the grain, or seasoned piece of iron.

Finally, skill plays a role. If you apply a sideways force to the edge while chopping, there's more potential for damage than if you have excellent form and make perfectly aligned cuts.
 
I have a bamboo grove in my back yard.

Experimented this weekend with a WW II by K.S. spear of Trident mark,kami 16.5" this weekend.

Convex edge put on by me with professional equipment. Not shaving sharp, but sharp.

Hit rocks, rolled edge back 1/8", no cracking, will resharpen just fine.

Bottom line, thin edge down as much as needed, not as much as you think, and you will be fine.

Regards,

Steven Garsson
 
Too Sharp:
When you start having problems keeping the edge attached to the blade (as in chipping or bending). Depends on materials, design, how you use the blade, and what you use it on. There is no right or wrong answer; use what works best for you.

n2s
 
It is becoming apparent to me that once a convex edge bevel is in place, you don't have to worry about putting on too fine an edge. Recently I have been using the tip of one khuk for whittling, holding the work piece in the free hand and applying thumb pressure to the spine. Very detailed carving is possible this way, and the softer tip and curved area by the cho hold an edge very well during "low impact" cutting.

Yesterday I used this same khuk to cut up about 100 yards of old lawn edging (plastic) into 1.5' chunks for disposal. This was all cut against a chopping block and involved some unavoidable blade contact with mineral soil. Afterwards, about five passes per side with the chakma and a few minutes with a strop and green compound put everything back in order. A straight edge bevel would have required a ceramic rod at the very least, and probably more.
 
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