Can you ever get a knife, too sharp?

[Uncle Timbo]

I figure that's a loaded question, but I'm serious. I think a lot of you know how I feel about my knives and sharpening them.

Dad always taught me there were two ways to sharpen a knife, one was his, working edge. This one was for cutting up cardboard and the like. Rough use, if you will. Not a really steep angle. The other was his, show off, shave hair, impress your friends edge. He likened this one to sharpening a pencil to a very fine sharp point. Then he said if you were to use that edge in every day life and bear down on it, it just wouldn't last very long.

So I honestly ask, can you get a knife too sharp for it's own good? What are you going to do with it?

 

[jc57]

Perhaps "the wrong kind of edge for the intended purpose" might be a better wording. An edge that is highly polished and very thin behind the edge might be wonderful for shaving, or push cutting through some vegetables. But it might be horrible for cutting rope.

 

[Wowbagger]

Can you ever get a knife, too sharp?

Me ?
ALL of my knives are too sharp.
They work well.
Anything less . . . sucks.

PS : I have tried "working edges" (I'm looking at you S110V). . . and toothy . . . toothy 's OK I guess . . . I don't have much use for it. I do a lot of trimming and push cutting. Polished and silly sharp works better for all that.

PPS : someone here has a quote on their page that says something like "Polished and refined is an EDGE; anything else is just a saw".

PPPS : my saying in another forums is "Good enough is good enough but better is better".

 

[John Watson]

Having an edge not suited to the task can be frustrating. I once had a small Griptilan that was razor sharp and I needed to cut one of those elastic bungee cords open to get at the individual stands inside. The outside nylon was so slick the edge just slid over it without cutting. The knife would shave without any problem but the edge didn't have enough tooth to catch the material I needed to cut.

 

[HeavyHanded]

I've done enough testing to see a correlation between the amount of tooth an edge has or does not have and its retention at a given task draw or pressure cutting.

Tailor the edge to the task. For general use it often pays to match your edge with a specific maintenance scheme than the perfect edge finish. Whatever you can refresh most easily is a big advantage.

 

[Wowbagger]

The outside nylon was so slick the edge just slid over it without cutting.

That's a geometry problem. Angle too wide; probably convexed (too much).
I can already feel one of my shallow angle knives in my imagination . . . in my hand . . ., sharpened on an Edge Pro at a consistent shallow angle, just slicing into that bungee . . . easy as cake

Watch some Murray Carter vids for geometry . . . then . . . keep going on the Edge Pro to a polished edge . . . toothy be dambed . . . and THEN see what she'll do.

Now, now . . . of course cutting butt loads of old dirty rope I know saws work better than knife edges . . . Ankerson proved it over and over. Not much fun though. Really.

 

[Obsessed with Edges]

'Sharper' always comes with thinner geometry, i.e., thinner apex, thinner steel behind it, in general. It's possible to thin a blade and it's edge too much, if the tasks then given to it are prone to rolling or chipping the edge too easily. I have a couple or three knives of my own that I thinned, and thinned some more, just to see how cutting would improve or change. At least one of them is thin enough now, it's more prone to damage (edge rolling & denting) with light impacts on hard material (staples in cardboard, etc). So I reserve that one for lighter use. I have another one in ZDP-189, extremely hard, which broke off a tip while stropping the edge (tip dug in), immediately after I'd thinned it to better slicing geometry. There's always some trade-off between sharpness and strength.


David

 

[Uncle Timbo]

David - if you broke it's tip while stroping, I can only imagine how thin you had that one. Was it a kitchen knife?

 

[Obsessed with Edges]

David - if you broke it's tip while stroping, I can only imagine how thin you had that one. Was it a kitchen knife?

Actually, it wasn't that thin, or at least as thin as I initially assumed. It was a Kershaw Leek in ZDP-189, with a very, very pointy tip on it, straight from the factory. This steel is known to be brittle, because it's extremely hard (usually treated well into the 60s, HRC). I thinned it down to around ~30° inclusive, the angle estimate based on a photo I took of the cross-section of the broken tip, with a USB microscope (see pics below). A combination of the extremely hard, brittle steel and the pointy, pointy tip was already risky; I thinned it a bit more, and minutes after I finished that, I managed to dig the tip into the strop, and SNAP it went.

I've since fixed it though, by regrinding the tip. And that knife is also now reserved for lighter duty.


David

 

[Chris "Anagarika"]

David,

Had happened to me once on a Stretch but I forgot whether it was VG10 or HAP40. Just got it thinned down & was stropping on paperboard + green CrO. Taught me a lesson about pressure .

 

[scott.livesey]

can you make a knife too sharp? no. can you make a knife so sharp that the blade is easily damaged when doing routine cutting? sure, an ultra fine edge on a kitchen slicer will be damaged when a ham handed helper rock cuts carrots using way too much force. i no longer go for max sharpness, i tailor sharpness to the user and the job being done.

 

[Uncle Timbo]

Actually, it wasn't that thin, or at least as thin as I initially assumed. It was a Kershaw Leek in ZDP-189, with a very, very pointy tip on it, straight from the factory. This steel is known to be brittle, because it's extremely hard (usually treated well into the 60s, HRC). I thinned it down to around ~30° inclusive, the angle estimate based on a photo I took of the cross-section of the broken tip, with a USB microscope (see pics below). A combination of the extremely hard, brittle steel and the pointy, pointy tip was already risky; I thinned it a bit more, and minutes after I finished that, I managed to dig the tip into the strop, and SNAP it went.

I've since fixed it though, by regrinding the tip. And that knife is also now reserved for lighter duty.


David

Unrelated to sharpness, but I fixed a coworkers Kershaw/tanto blade after he thought it was a screwdriver. I gave it back to him with my Dads famous "working edge." I should of given it back to him with a, "straight slot" edge.

Scott, I'm with you.

 

[stitchawl]

I don't think you can make an edge too 'sharp.'
I DO think you can make a sharp edge too 'thin.'


Stitchawl

 

[Uncle Timbo]

I don't think you can make an edge too 'sharp.'
I DO think you can make a sharp edge too 'thin.'


Stitchawl

Don't they sort of go hand in hand?

 

[The_Knife_Man]

I don't think a knife edge could be to sharp.

 

[Uncle Timbo]

Knife Man, I respect your opinion, just like I respect everybody else's on here. My point was to start honest debate.
My thoughts are that a knife can be too sharp, but then again, possibly I don't know your all's intended use?
I guess my use for a knife is purely utilitarian. I want the edge to work for me doing menial tasks and I want it to last as long as it can.

 

[Obsessed with Edges]

My own approach in sharpening is to make an edge as sharp as I can make it, within a fixed target range for the geometry of the edge. That usually gets it to at least shaving, to some degree. For knives that I know don't actually need to be that sharp, keeping the edge geometry thin enough means that when the shaving edge goes away (and that's usually pretty soon), the working edge that remains will still be plenty sharp enough for the 'real work' I intended it to do, and it'll do it for a respectable length of time. For me, that means edge geometry at or below 30° inclusive, often down to 25° inclusive or so, for every single knife I own and use. Lose a little crispness at the apex, and the edge still works for most normal cutting tasks. And a thinner geometry will also be easier and faster to restore to full sharpness, when it needs it.


David

 

[BluntCut MetalWorks]

Yes, edge can be too sharp - In context of practical/common edge geometries and uses, i.e. excluding outlier geometries (e.g. at extreme bevel 180 - epsilon or epsilon degrees) and odd usages.

Too sharp = not able to sustains/supports physical interaction within expected services/functional life (against an optimal baseline/reference). When an apex width prematurely widened, includes the widened apex width is within or thicker than functional width range, therefore it is too thin (relative to reference).

Discussions w/o fixed baseline/reference, the 'too' line depends on: steel properties; interactions; technique; actual & perceived data, etc...

Example:

*psi # is arbitrary for discussion purpose rather than actual

Optimal reference chopper can cut N wood dowels used J(energy of work), with apex started at 10um and ended at 12um. Where 1um/inch can supports 1K PSI and chopping involves 9.999K PSI

1. When a chopper with starting apex at 3um quickly folded and or chipped to 15um width, which then used more than J energy to complete the workload. Obviously case of too sharp.

2. When a chopper with starting apex at 3um quickly folded and or chipped to 6um subsequently to referenced/optimal geometry, which then used a minute less (perhaps by 2 chops of slightly more penetrating chops) than J energy to complete the workload. It is still a case of too sharp because of 2 premature edge damages which resultant edge thickness may not be lucky next time. While ignoring quality of first 2 cuts and a few microns of blade width.

 

[Petunia D. Feeble]

Yes, edge can be too sharp - In context of practical/common edge geometries and uses, i.e. excluding outlier geometries (e.g. at extreme bevel 180 - epsilon or epsilon degrees) and odd usages.

Too sharp = not able to sustains/supports physical interaction within expected services/functional life (against an optimal baseline/reference). When an apex width prematurely widened, includes the widened apex width is within or thicker than functional width range, therefore it is too thin (relative to reference).

Discussions w/o fixed baseline/reference, the 'too' line depends on: steel properties; interactions; technique; actual & perceived data, etc...

Example:

*psi # is arbitrary for discussion purpose rather than actual

Optimal reference chopper can cut N wood dowels used J(energy of work), with apex started at 10um and ended at 12um. Where 1um/inch can supports 1K PSI and chopping involves 9.999K PSI

1. When a chopper with starting apex at 3um quickly folded and or chipped to 15um width, which then used more than J energy to complete the workload. Obviously case of too sharp.

2. When a chopper with starting apex at 3um quickly folded and or chipped to 6um subsequently to referenced/optimal geometry, which then used a minute less (perhaps by 2 chops of slightly more penetrating chops) than J energy to complete the workload. It is still a case of too sharp because of 2 premature edge damages which resultant edge thickness may not be lucky next time. While ignoring quality of first 2 cuts and a few microns of blade width.

When your answer to the question is this ^ you've gone too far. It's a keen wedge that you use to open boxes. Don't over think it.

I'll agree with whomever said it should be tailored to the task(s) at hand. It can't be too sharp or too thin for shaving, but it certainly could be too sharp or thin for chopping wood, breaking down a refrigerator box, etc.

 

[JJ_Colt45]

I'm not sure I would ever use the term "too sharp" ... but I believe you can definately sharpen a blade til its to thin to last long ... it may shave like a razor but for how long?

And as some said already ... every edge sharpened to the geometry that best suits its intended use is sharp ... sometimes that's staying at a very toothy low grit instead progressing up to fine micron polishing of the edge to reach the "mirror finish".