Too sharp?

[KennyB]

What amount of wear is acceptable on an edge after cutting paper, hair and plastic?

I ask because, genearlly after shaving or cutting some hair up, my edges have barely visible dings and rolls at 30x magnification. This bothers me; I have no practical reason for being bothered by this, it's just an obsession. In any case, let's just pretend I have a valid reason for wanting to avoid this.

Is it unavoidable? I've tried some very obtuse bevels, and I've used 440,440HC,AUS8 and S30V and all have the same level of wear, so I'm kind of assuming that steel is pretty much just not structurally strong enough at that small of a scale not to be deformed a little bit.

That being the case, I'm wondering what an acceptable level of wear for what cutting material is acceptable. I know that's not a very easy question to answer, especially because the general way to figure that out would be what kind of wear can I accept and work with, but as I said this is purely an obsession, the wear I'm encountering doesn't effect my use of the knife at all, I'm just obsessed with maintaining a roll/ding/nick free edge and wondering if that's even possible at the scale I'm talking about.

Just for specifics, since that would make it easier... Most of my edges I cannot measure above .001". Meaning that, I can set my micrometers to .001", and can wiggle my edge around between the anvil and the heel a good bit. Even on edges I grind with some pretty obtuse bevels this is true, so let's just assume we're talking about an edge that is .001" or less.

The hair and paper I'm cutting are both .0015-.0017" most of the time, so not very much material at all. I'm also using 30x mangification to see these "dings and rolls" but I can't really measure them, all I can really do is leave some hair on my blade when looking through magnification and compare the size of the ding to the size of the hair. Going by that, I would say that the dings are maybe 1/5th to 1/10th the size of the hair, and the edge itself is too small to really quantify.

When talking about such small scales it seems pointless to worry about it--I realize that-- but then again most of this is pointless for me since I'm just doing it for hobby/challenge. I don't know if anyone will be able to relate to this and be able to give me much information though. I mean, I doubt many people have wondered what kind of damage a piece of paper does to a blade in the .0001" scope of things and busted out a electron microscope to get various readings on wear, but that's what I would be interested in hearing about.

In any case though, basically, can you have an edge so sharp that it's never not going to encounter wear? I'm not talking about a bevel that's so acute it rolls or deforms, I mean the edge itself. To me it seems that there's really no way any material is just going to stay rigid and in place at that level, even if it is steel. I'm not sure if that's a sound conclusion to come to though based on the type of wear I'm seeing.

So yeah, purely an academic ( for lack of a better term ) question about things on a scale that have no real practical purpose, but are driving me nuts. My problem is I want a blade free and clear of defects I can see at 30x magnfication, but just cutting simple things like plastics and what not produces visible defects at that level. I'm wondering if it's something I'm doing, or if it just can't be avoided. I figure the latter, since if I stop seeing defects at 30x, I bet I would still see them at 300x.

 

[eKretz]

I'm not sure if hair should be causing that kind of damage, but on a very well sharpened blade, you have the edge sharpened to such a point that it is going to be pretty weak. You can kind of get an idea by thinking about steel shim stock. .010" is pretty strong and tough to tear or bend by hand, but .001" is easily tear-able and bendable almost like aluminum foil. A properly sharpened edge comes to quite a bit smaller thickness than .001" - something on the order of .000030"-.000040" - or 30-40 millionths of an inch. So as you can imagine, with a thin edge, it doesn't take a lot of force to do damage to even a properly sharpened edge with no burr.

 

[HeavyHanded]

Another thing to keep in mind is that with a highly polished edge every little ding, nick, and roll will be visible at 30x and most will be visible to the unaided eye with the right lighting. How obtuse of an edge are we talking about?

In any case though, basically, can you have an edge so sharp that it's never not going to encounter wear? I'm not talking about a bevel that's so acute it rolls or deforms, I mean the edge itself. To me it seems that there's really no way any material is just going to stay rigid and in place at that level, even if it is steel. I'm not sure if that's a sound conclusion to come to though based on the type of wear I'm seeing.

I think that sums it up. A knife is a consumable tool. Can't say for sure, but all knife edges probably leave some of itself behind for every cut they make, how much depends on the relative differences between the hardness of the materials, edge geometry, and type of edge grind. Just sitting there, corrosion is dulling the edge of unprotected knife blades, even if it is stainless (though not very much and a little film of oil will negate this affect, but you get the picture). Any cutting operation begins the process of dulling the edge. That said, a little bit of casual use shouldn't result in visible edge damage...

You raise an interesting question though, I'll have to pick the father-in-law's brains on this one, he actually had access to a scanning electron microscope while he was designing cutters for industrial applications.

 

[hardheart]

This is kinda tough to track. The very existence of razors kinda makes these edges sound very poor. Imperfections in a straight razor visible at 100X can make it pretty uncomfortable to shave with, so they certainly can't have visible damage at 30X and be useful. A rehone before every shave just isn't normally done, and wastes the razor, but you would need to if this was the case. The scale for your dings isn't too reliable, the thickness of hair can vary more than an order of magnitude, from less than 20 microns to close to 200.

 

[richard j]

i made a knife that i have chopped hard elm, ash, osage orange and oak with, cut up water heater boxes into small pieces and it would still push cut paper and shave hair. if you look at the edge with the naked eye you cant see any deformation but i have never looked at the edge under magnification yet. i dont think sharpness has anything to do with edge wear but how its shaped might have some effect on how it wears (but thats just my thinking). the edge on the knife i'm talking about has a half convex chisel grind.

some guys obsess way too much with a mirror edge and if it gets a little smudge they HAVE to take it out or it bugs them. to me, this takes life from an edge. i wouldnt worry about your edges and use the knife . worrying will give you grey hair

 

[unit]

some guys obsess way too much with a mirror edge and if it gets a little smudge they HAVE to take it out or it bugs them. to me, this takes life from an edge. i wouldnt worry about your edges and use the knife . worrying will give you grey hair

I have walked both sides of that fence. Which ever side makes you feel best is where you ought to tread, but honestly no one else really cares if the knife in your pocket has a mirror polish, and whatever gets your work done is all you really need.

If you need a scope to see the problem, I am not sure I would call it a problem...it might sound smarta$$ed to say, but I do not EDC a scope so why have concern?...again, it is all about keeping yourself happy, but I discovered I am quite happy when I use the heck out of my knives and then NEED to sharpen ("need" by almost anyone's standards...not just BF knife nuts like us).

OTOH, if there is visible (30X) edge deformation from a hair, and in an academic sense you want to know why...perhaps you have a very very small wire edge? It just does not seem logical that a hair could degrade an edge at that magnification (see razor discussion above).

Have fun!

 

[HeavyHanded]

One other thought on this - occasionally when changing the edge angle on a knife I'll get lazy when polishing out some of the heavier grind gouges. As the edge progresses to the finer honing stones these "knicks" remain, and if not noticed initially could be mistaken for edge damage.

 

[Jason B.]

Why is important to know things like this? because its like learning anything, you don't want to do it halfa$$ed.

If everyone had the attitude of "well thats good enough" then everything around you would break constantly. If you were a astronaut would you want the rocket scientist to say "it good enough"??? probably not.

If you think even something as simple a cutting paper is not doing damage to your edge then your just fooling yourself. From the moment you stop sharpening the edge is constantly going dull, from the atmosphere causing micro corrosion to the edge, to any and all contact that the edge comes into. Everything in life as we know it starts on the atomic scale and only gets bigger, probably the reason we use things like SEM's to understand things like steel and edges or anything too small for the eye to see.

For some they have no need to understand all that can be understood about sharpening but there's no need for them to call the rocket scientist a fool for knowing to much.


Kenny, kudos to you for wanting to know all the complex details. The problem you may be having is understanding the edge geometry vs material contact. Things like plastic will cause a edge to deform quickly and create lateral stresses in the edge, paper will cause pure abrasion and make a edge "toothy", Hair is surprisingly strong and in comparison would be like cutting copper of the same thickness. 30x is good but 100x or more really brings you to a new understanding of what happens.

Here are pics of edge that are worn, damage usually able to be felt but unable to be seen by the eye .

This is a edge finished by a DMT EEF, to the eye is looks like a even finish but up close you can see all the smaller lines of scratches made by each pass on the stone. You can also see the small burr and left over plastic deformation from the sharpening process at the very edge.

This is what's left of a microbevel on S90V after some extreme cutting, note this micro bevel cannot be seen until 100x pic at 400x

 

[KennyB]

Why is important to know things like this? because its like learning anything, you don't want to do it halfa$$ed.

If everyone had the attitude of "well thats good enough" then everything around you would break constantly. If you were a astronaut would you want the rocket scientist to say "it good enough"??? probably not.

If you think even something as simple a cutting paper is not doing damage to your edge then your just fooling yourself. From the moment you stop sharpening the edge is constantly going dull, from the atmosphere causing micro corrosion to the edge, to any and all contact that the edge comes into. Everything in life as we know it starts on the atomic scale and only gets bigger, probably the reason we use things like SEM's to understand things like steel and edges or anything too small for the eye to see.

For some they have no need to understand all that can be understood about sharpening but there's no need for them to call the rocket scientist a fool for knowing to much.


Kenny, kudos to you for wanting to know all the complex details. The problem you may be having is understanding the edge geometry vs material contact. Things like plastic will cause a edge to deform quickly and create lateral stresses in the edge, paper will cause pure abrasion and make a edge "toothy", Hair is surprisingly strong and in comparison would be like cutting copper of the same thickness. 30x is good but 100x or more really brings you to a new understanding of what happens.

Here are pics of edge that are worn, damage usually able to be felt but unable to be seen by the eye .

This is a edge finished by a DMT EEF, to the eye is looks like a even finish but up close you can see all the smaller lines of scratches made by each pass on the stone. You can also see the small burr and left over plastic deformation from the sharpening process at the very edge.

This is what's left of a microbevel on S90V after some extreme cutting, note this micro bevel cannot be seen until 100x pic at 400x

I thought I remembered hearing the thing about hair being as hard as copper of the same diameter. Glad to see I didn't just imagine it.

So it seems to me that I need to get a 100x scope to check out all the little dings and nicks I can't see at 30x. I'm wondering since I can just barely make them out as glints of light at 30x, if 100x will really reveal their true character to me.

I'm thinking that the glints I'm seeing are from the paper, because it happens after making quite a few push cuts through a piece of paper. Seeing as they're still so small to barely be seen under 30x, it seems like that would be the right scale for that too, right?

I think I'm going to go get a cheap 100x and keep my edges as they are for now. I looked up the prices on a 300-400x USB microscope, but I'm not sure I want to spend the cash right now, especially since it seems like it would be kind of meddlesome as I often use magnification during the sharpening process to see what's going on.

For those of you wondering how obtuse I'm talking about, I've tried edges with 50 degree inclusive bevel angles and still encountered this, and I use a strop and a block of wood to remove burrs and wire edges. I'm not too sure what other part of my sharpening processes might be forming an edge that is easier to damage by this.

I think you pretty much confirmed my suspicions that these materials are doing more wear than I think though, knifenut1013. I knew I had heard that about hair somewhere before, and that's what originally made me have the idea. I suppose my only real question is: Is steel any softer at that scale? I mean, steel is supposed to be harder than copper, does copper deform the edge because it's harder than the steel at that scale...or because the steel making contact is so many times smaller that it'd be like dropping a big piece of copper stock on a piece of sheet metal and expecting the sheet metal not to deform?

 

[Jason B.]

I think you pretty much confirmed my suspicions that these materials are doing more wear than I think though, knifenut1013. I knew I had heard that about hair somewhere before, and that's what originally made me have the idea. I suppose my only real question is: Is steel any softer at that scale? I mean, steel is supposed to be harder than copper, does copper deform the edge because it's harder than the steel at that scale...or because the steel making contact is so many times smaller that it'd be like dropping a big piece of copper stock on a piece of sheet metal and expecting the sheet metal not to deform?

Exactly, If I were to put a piece of hair in those pictures it would look like a giant tree

 

[David Martin]

i made a knife that i have chopped hard elm, ash, osage orange and oak with, cut up water heater boxes into small pieces and it would still push cut paper and shave hair. if you look at the edge with the naked eye you cant see any deformation but i have never looked at the edge under magnification...

some guys obsess way too much with a mirror edge and if it gets a little smudge they HAVE to take it out or it bugs them. to me, this takes life from an edge. i wouldnt worry about your edges and use the knife . worrying will give you grey hair

Richard, I so, agree with this . There are other things more important to worry about in life . DM :thumbup:

 

[Convectuoso07]

Richard, I so, agree with this . There are other things more important to worry about in life . DM :thumbup:

These don't have to be mutually exclusive guys. It's quite possible to be an outdoor enthusiast who chops trees down daily with a pocket knife and still be academically interested in the subject. I mean, we're all spending at least a little time sitting in front of a computer screen (a fact I'm becoming more and more embarrassed about ) so the "get out and use the knife" mentality is really just BS.

 

[myt132-cu]

A couple things; Did you try marking the knife blade with a magic marker, then take a hair and cut it at that exact spot so that you could see if it deformed the edge right there? That would be interesting to see. The steels you mention are on the soft-ish side. Even S30 is only 58or9, but I still have a hard time buying that a hair will deform an edge.

This may sound counter intuitive, but how high are you going on the finish of your edges? If you aren't polished out very smoothly, it could be pretty easy to deform some of the "micro-serrations".

Hard Heart brought up a good point; whiskers is much tougher than hair, and straight razors have an extremely fragile (thin) edge. Straight razors are also polished to the nth degree, so again with the question of how polished are your edges?

If you are on the hunt for a really cheap microscope, RadioShack sells a 60x-100x for about $15. It's obviously low quality, but you can see some stuff with it. If I could find mine, I would polish the edge of one of my German kitchen knives, since they are only 54-56 RHC, make a mark on it, and cut a hair on that spot just to see if it makes a dent in the edge. If I could find my damn microscope I would like to see this as well.

Another thing I don't see mentioned, is what type of edge bevel you are using. If you are using paper wheels, you are putting a hollow ground EDGE on your knife, which, to my knowledge, is the weakest edge you can put on a blade. Yes, of course, they do get lickity sharp, but the lack of supporting steel behind the very edge makes them prone to deform very easily.

If that IS what you are doing, try convexing the blade. The results will speak for themselves. Just MHO.

 

[dsmegst]

Another thing I don't see mentioned, is what type of edge bevel you are using. If you are using paper wheels, you are putting a hollow ground EDGE on your knife, which, to my knowledge, is the weakest edge you can put on a blade. Yes, of course, they do get lickity sharp, but the lack of supporting steel behind the very edge makes them prone to deform very easily.

The amount curving you would get from an 8-inch paper wheel on an 1/16 inch or less secondary edge is so small that it's practically a V edge. I doubt there's enough difference between a conventional V edge and a paper wheel edge (assuming we're talking about the same angle).

At least in my experience, a 30 degree inclusive edge from the Sharpmaker performs the same as the one from the paper wheels. The only difference is the amount of polishing I get from the paper wheels and the amount of time I saved.

I won't compare this to a convex edge as none of my folders are convex.

 

[richard j]

david martin, last week when a member came down to get some knives sharpened we talked about the wheels i use and how they save time that can be used for better things that are relaxing, like chasing the better half around the house .

 

[richard j]

myt132-cu, a while back someone posted a diagram of what you are talking about. it shows the contact area to be so small that the edge is more or less flat and not like a hollow grind. if you were sharpening a knife made from 1/2" thick stock then you might see a slight hollow edge.

 

[Jason B.]

I guess all you anti time wasters need to get off the web too, wouldn't want to waste too much time sitting in front of these silly things......