What is sharp?

[Pelagic]

Just curious what your definition of sharp would be if you had to pick one.

[vivi]

I don't consider geometry and sharpness the same. Sharpness to me is how refined the apex is, while geometry is its own distinct category.

[weeping minora]

How thin/keen the apex is. Being able to cut using the least amount of pressure will be a direct result of the former. Sharpness is a result of how refined the apex is.

[Tucson Tom]

I may not be able to define it, but I know it when I feel it.

[Bdubs808]

To me sharp means the opposite of dull; meaning it will cut stuff.

[The Meat man]

I voted for edge sharpness.


I agree with Vivi. Edge sharpness and ease of cutting are connected but not the same. For example, I routinely get my axes sharp enough to shave and slice paper, but put them up against a moderately dull kitchen knife in a cutting contest, and the kitchen knife would still probably win.

[Pelagic]

I was thinking about this, and the answer isn't incredibly clear to me. Edge thinness/keenness seems to be one single attribute, while being able to make cuts with extremely light pressure is a function of both edge keenness and geometry (among other factors). A blade could be sharpened at 60 degrees per side and have a perfectly formed apex 0.1 microns thick, but how sharp is it?

[Bloke]

I truly don’t know but I do know edge geometry is key when it comes to actually cutting stuff. Evil D did some very interesting stuff on a thread titled Fun with edge geometry (I think) a while back which highlighted that.

As far a straight out sharp goes I think if an axe, knife or tin lid shaves hair say as well as a razor they’d all have to be sharp irrespective of geometry.

[weeping minora]

I'm not sure how geometry got pulled into the question of what is sharp? :confused: Would have made more sense if the OP asked what cuts(?) for the poll to have geometry brought into this. Sharpness only involves the apex of the knife and is the initiator of any cut. Without a sharp apex, there is far more resistance in making any effective cut; regardless of geometry beyond that point. The argument of what geometry is best for cutting becomes a gray area when the factor at play is what's being cut? What steel is used for that cut? Heat-treat? Geometry? Etc. You can effectively cut a hair that won't reach any farther than the apex before it "pops" with an edge that's 30 degrees, just the same as an edge that's 12 degrees, if the steel is sharpened accordingly. Once material/food/etc. contacts more than just the apex does the rest of the knife geometry start to "cut", IMO/IME.

[Spydermane]

Is there a standard for a doctors scalpel ?
That's probably a good standard at some level

[ZrowsN1s]

What is sharp? My spyderco collection :D

[Larrin]

How thin/keen the apex is. Being able to cut using the least amount of pressure will be a direct result of the former. Sharpness is a result of how refined the apex is.

I would think of it in the opposite direction. How thin the apex is may correlate with sharpness but isn’t a definition.

[bearfacedkiller]

Sharpness can be both defined and quantified. It is the width of the apex measured in microns. Typically an apex of 1 micron or less is considered very sharp.

This is different than refinement. Past a certain point in your progression of stones you do not actually make the apex much smaller but rather just clean up the scratch pattern on the apex.

Edge geometry is yet another separate factor all together. It effects cutting performance but it is not sharpness.

This is how I understand it.

[guywithopinion]

For me, it doesn't seem useful to have a notion of sharpness that I can't measure. I'm sure the thinness of the apex is technically the measure of sharp, but I can't whip out my electron microscope to evaluate that.

How easily it cuts through things that don't offer resistance seems to me to be a more practical metric. Cutting printer or phone book paper, or arm hair with little effort/resistance. The poll choice is more general, and cutting rope or cardboard or a steak or a 2x4 with the lowest effort will depend a lot on the overall geometry.

[Pelagic]

I'm not sure how geometry got pulled into the question of what is sharp? :confused: Would have made more sense if the OP asked what cuts(?) for the poll to have geometry brought into this. Sharpness only involves the apex of the knife and is the initiator of any cut. Without a sharp apex, there is far more resistance in making any effective cut; regardless of geometry beyond that point. The argument of what geometry is best for cutting becomes a gray area when the factor at play is what's being cut? What steel is used for that cut? Heat-treat? Geometry? Etc. You can effectively cut a hair that won't reach any farther than the apex before it "pops" with an edge that's 30 degrees, just the same as an edge that's 12 degrees, if the steel is sharpened accordingly. Once material/food/etc. contacts more than just the apex does the rest of the knife geometry start to "cut", IMO/IME.

Let's say you had 2 knives, A and B.

Knife A cuts carpet, rope, and cardboard just fine, taking moderate force.

Knife B seems to glide through all 3 mediums with noticeably less force than used on knife A.

You know nothing else about the knives. Which is sharper? (most would feel compelled to say knife B)

Does this comparison tell you which knife has the thinnest apex? (No)

That is how geometry is brought into the equation.

[Surfingringo]

I always find this topic a little perplexing. It seems so clear to me that it always surprises me that there is even any confusion over it. I'm not saying that my point of view is more correct than someone holding the opposite position, only that it seems clear to me. :-) I was quite surprised when I looked at the results of the poll. I honestly expected it to be 10-1 in favor of the first option.

Here's my thinking on the subject. I believe that we all have an inherent and universal idea of what the word "sharp" means. It means something having a narrow apex relative to similar objects. If you bump your hip on the corner of the bar you say "man, that's a sharp corner". You are describing the width of the apex, not the slicing ability. If you are driving you might encounter a "sharp turn". Again, you are describing the apex (that's a bit of a stretch but the same idea).

Personally, I think that describing a knife with good cutting geometry and a dull edge as "sharp" is a misuse of the word. I also kind of think that some folks saying it might not even believe it when provided evidence to the contrary. Here's an example. Imagine you have splitting maul with a hair whittling edge and a dull paring knife. Have a person who is defining sharpness by blade geometry use both knives to cut up some boxes, or maybe slice some cheese and ask them which knife is sharper. When they answer that the paring knife is sharper, gently run both edges across their forearm. After cleaning up the blood left by the splitting maul, ask them if they would like to change their answer.

I understand what folks are getting at with trying to use the word "sharp" to describe a knife's cutting geometry but i think a different word should be used because sharp is already taken and means something else. :)

Anyway, as I said in the beginning, this is just the way I see it and though it seems very clear to me, I would love to hear the rationale of anyone disagreeing with my point of view.

[jackh]

I voted for sharp meaning the tool cuts with it's intended purpose as good as possible. I think this would hold true for people who carry a knife every day or a chef. I feel the edge apex's sharpness, keenness, etc. is a smaller part of the big picture. The big picture includes blade thickness, grind, intended use, etc.

[Pelagic]

I always find this topic a little perplexing. It seems so clear to me that it always surprises me that there is even any confusion over it. I'm not saying that my point of view is more correct than someone holding the opposite position, only that it seems clear to me. :-) I was quite surprised when I looked at the results of the poll. I honestly expected it to be 10-1 in favor of the first option.

Here's my thinking on the subject. I believe that we all have an inherent and universal idea of what the word "sharp" means. It means something having a narrow apex relative to similar objects. If you bump your hip on the corner of the bar you say "man, that's a sharp corner". You are describing the width of the apex, not the slicing ability. If you are driving you might encounter a "sharp turn". Again, you are describing the apex (that's a bit of a stretch but the same idea).

Personally, I think that describing a knife with good cutting geometry and a dull edge as "sharp" is a misuse of the word. I also kind of think that some folks saying it might not even believe it when provided evidence to the contrary. Here's an example. Imagine you have splitting maul with a hair whittling edge and a dull paring knife. Have a person who is defining sharpness by blade geometry use both knives to cut up some boxes, or maybe slice some cheese and ask them which knife is sharper. When they answer that the paring knife is sharper, gently run both edges across their forearm. After cleaning up the blood left by the splitting maul, ask them if they would like to change their answer.

I understand what folks are getting at with trying to use the word "sharp" to describe a knife's cutting geometry but i think a different word should be used because sharp is already taken and means something else. :)

Anyway, as I said in the beginning, this is just the way I see it and though it seems very clear to me, I would love to hear the rationale of anyone disagreeing with my point of view.

Thank you for weighing in, Lance.

If you bump your hip on the corner of the bar, and the angle is extremely obtuse, it wouldn't be the same as bumping into a corner that is extremely acute, regardless of "apex" size.

It's not that a blade of good cutting geometry and a dull edge would beat any and all knives of extremely sharp edges. Think about this:

Knife A is a spyderco Endura sabre grind with a 17 dps edge, finished and finally stropped down to 0.003 micron (~5 million grit).

Knife B is a spyderco Endura FFG with a 13 dps edge, finished and stropped down to 0.1 micron (200k grit).

Knife A has a much thinner apex, but knife B will often cut better.

Neither blade is dull (in fact both can easily whittle a hair), but cutting ability will be different.

I think the difference could be this: sharpness and cutting ability aren't the same. In the real world, cutting ability (imo) is virtually always viewed as an indication of sharpness.

In normal settings, it would most likely prove difficult to tell someone "sure, your knife cuts better, but mine is sharper".

No example is perfect and I'm sure mine have flaws. Examples exist to highlight underlying concepts, not to insist that the subject matter directly applies.

I feel that this is an interesting issue.

[Woodpuppy]

“Sharp” to me implies a positive measure of performance. Edge geometry plays a part in performance of course; and this is without getting into if a given edge geometry will last under the use its given. When I’m sharpening my knives, they are “sharp enough” when they easily shave. When my kitchen knives will no longer cut tomatoes without deforming them, they are no longer sharp enough. But that same edge on an edc may still be useful.

[Surfingringo]

....In normal settings, it would most likely prove difficult to tell someone "sure, your knife cuts better, but mine is sharper".

Not if you run both edges across their forearm per my example. :cool: :D


Here’s another example for those defining sharpness by blade geometry. I just made some burritos and had to cut a couple of slices of cheese. I had a thin butter knife and a freshly sharpened (hair whittling) cruwear Military with a 10 dps edge. I instantly reached for the butter knife because I knew it would slice the cheese with far less resistance than the Millie. So here’s my question for those defining sharpness by blade geometry. Is anyone really willing to take the position that that butter knife is sharper than the Military?? If not then doesn’t that kind of threaten the logic of your definition of sharp?

Another problem of defining sharpness by cutting ability is it is a very arbitrary definition. Ability to cut what? Carpet? Meat? Cheese? Firewood? A chisel will cut a notch in hardwood better than a bread knife. So it is sharper? But a bread knife will cut bread better than a chisel. So maybe it is sharper? This whole exercise seems like we are taking a very simple and clearly defined word and trying to make it mean something else.