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Does anyone know, or know how to find out exactly how thick or thin the actual cutting edge needs to be? This would be for a very sharp blade, about like a razor blade.

I have read that the edge thickness needs to be 3 Microns or less, but I don't know how someone would go about measuring it

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I would say it's also about blade geometry and heat treat with regard to a knife, so not sure just determining edge thickness will "cut it". smile

My understanding and I'm by no means an expert is that they typically use a gaussian beam to get a true edge thickness determination. There may be other means, but that's what I've read to be the true test.

Since you didn't mention the purpose behind your question I may be completely off base, but I think what you may want is a Catra test. I believe if you go to their website they will rent the testing machine or perform tests for you. I have no idea what it costs, or whether what you're trying to do really gets to that level, but catra is the yard stick most use to truly measure how sharp a blade is. For whatever that's worth.


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Originally Posted by mtnman1
I would say it's also about blade geometry and heat treat with regard to a knife, so not sure just determining edge thickness will "cut it". smile

My understanding and I'm by no means an expert is that they typically use a gaussian beam to get a true edge thickness determination. There may be other means, but that's what I've read to be the true test.

Since you didn't mention the purpose behind your question I may be completely off base, but I think what you may want is a Catra test. I believe if you go to their website they will rent the testing machine or perform tests for you. I have no idea what it costs, or whether what you're trying to do really gets to that level, but catra is the yard stick most use to truly measure how sharp a blade is. For whatever that's worth.


If anyone ever asks me if a knife I'm selling passes the catra test,or askes me about a catra test,or even mumbles that BS Dale ,it'll be yur fault ,and,I'll be rude to them,lol

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laughin'


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"Since you didn't mention the purpose behind your question"

I mean, what would be the maximum thickness of the edge for a knife (or razor) to be shaving sharp.

I read somewhere that obsedian (sp?) is probably the sharpest cutting tool in existance.

I think that edge geometry, heat treating, and type of steel, and also hardness would go more toward edge holding ability than how keen you can get an edge.

I used to work at a place where we sheared large pieces of aluminum. I know that the sheared edge would not last on aluminum, but it is sharp enough to do a job on your bare hands.

The same can be said for 303 Stainless, but I don't think either would have a very long lasting cutting edge.

There is also something about grain size and the finer the grain size, the sharper you can get the edge.

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I think, but do not know for sure, but the catra test is more to test how much cutting a blade will do and stay sharp by making controlled test on a given material.

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so not sure if this is just a generic question or if you have a specific purpose in mind. if all you want to know is how to measure edge thickness and or make something really sharp but it won't hold that sharp edge then that's more just a theoretical question. If you want it really sharp and want it to stay that way, then the whole Heat Treat, Blade geometry question comes into play. As far as minimum edge thickness to shave, I've heard Obsidian is something like 1 micron and the best steel can do is somewhere around 50 microns, but not sure where I saw that and may well be getting the facts a bit off.

Last edited by mtnman1; 06/27/12.

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i have an artical from the Knives 86 anual where on page 32 Ken Warner says that "the single flake spalled froma large chunk of obsidiian offers an egde 500 times sharper than the best surgical steel"
From reading more it seems that obsidian has a pure edge whereas a steel edge has minute saw teeth that tear rather than cut.

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eye surgery used to be done with obdidian flakes before the lazer came along. i've seen edges under a microscope whittle hair but some very smart edge people said that edge would last only as long as the first cut into whatever material. if a blade wo'nt do 3 or 4 deer & still shave then it's not good enough for me these days. the sharpest knife in the world is the diamond knife but if touched by one human finger it's ruined.just my opinion.---cranky72

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I dont know if this is the question! The best cutters come from blades which edge's are .010 thick and hollow ground on a big wheel. The great thing about big contact wheels it lets the person sharpen the knife many times before the edge gets thick. The steel is not as important as the grind and heat treat.




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The reason I want to know is, sometimes I have sharpened knives and the edge felt really sharp, from rubbing my finger across it. But, regardless of how sharp it felt, it would not shave nor cut paper without tearing it.

Then, I have felt other edges, maybe just slightly sharper, that would cut newsprint easily, in any direction, and shave like a razor blade.

I am trying to find out what would be the difference in cutting width between a blade that feels feels sharp but isn't and one that really is very sharp.

I think the ones I have tested that felt sharp but wern't sharp was because I may have been feeling the small burr on the edge.

There is usually a very sharp edge under the burr, but the burr has to come off before the edge could be considered shaving sharp.

As far as geometery, and heat treating, the steel could be from a fine knive, or a wedge or an axe. Get it sharp enough and it will cut. If dull, it will not.

One thing I think would determine just how sharp it is possible to get an edge would be the type steel. Some steel has finer grain size than others, and the finer grain size steel would get the sharpest. If you had a way to measure grain size, this might tell you how sharp your blade actually is.

I have read that you cannot sharpen a grain because as the matrix of the blade gets very thin, the grains will tear out instead of sharpen.

I would guess that razor blade manufacturers and scapel manufacturers have done research on which steel would get the sharpest. The sharpest edge in these two applications would be the most beneficial.

What about one single layer from a damascus blade, one that has about 612 layers? One layer in a 1/4 inch thickness bar of steel would be very thin.

I have read the same article about the obsidian, and that is what got me thinking about how keen a very sharp edge would actually be.

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NEARLY ANY STEEL IN THE WORLD CAN BE HONED SHARP ENOUGH TO SHAVE HAIR. THE BIGGEST FACTOR IN MANY STEEL ALLOYS IS WHAT IS CALLED abrasion resistance . take 2 knives or even axes & given equal sharpness the one that cuts the longest w/o edge damage with the correct rockweell hardness for each tool is generally considered a better alloy. i can take 1095 carbon & get it to shave the newsprint from a sheet of paper, also i can do the same with zdp189 or m390. the major differance is in cutting cardboard i may get 38 12 in. cuts with 1095 before the fine edge wears enough that it wo'nt easily slice sheet paper. zdp may go 65 cuts before the edge degrades to the same dullness as 1095 . m390 may go 85 cuts before it gets to the same dullness. the newer powder alloys usually have finer grains but i've seen very common older steels treated by a master knifemaker that do 3 or 4 tempers & double cyro cycles outcut much newer 3rd gen. powder steels.it's really about tweaking heattreats & using the most advantageous rockwell for that steel that give the best edgeholding . a garden hoe can be gotten sharp enough to shave but how long it shaves compared to a well heattreated super alloy is the big differance. hope this helps you--cranky72

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see 2 imadges of great eastern 1095 carbon honed on the edge pro to 6000 grit. although this is very very sharp i would probably stop at 1000 grit although both will easily shave newsprint. the 1000 grit edge would probably hold up better in field use cleaning animals--cranky72

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I understand about abrasive resistance and heat treating.

What I want to do is compare something like a cannon ball to a spear point, regardless of heat treating or type of steel. The cutting tool, regardless of material, might only be required to make one cut or shave one hair.

I want to know how sharp it has to be to make that one cut or to shave one hair. It doesen't matter what type of steel it is, or how it is heattreated. It could be aluminum, copper, brass, or even sliver of glass. Edge holding is not in consideration here.

For example, a cannon ball of 01 steel at RC 60 would hold a better edge than a bronze pointed spear, but the cannon ball would not cut as well. For a time, anyway.

I hope this explains what I am asking, like what is sharp and what is really sharp, and what is extremely sharp, and how much difference there is between sharp and extremely sharp, and how to measure the actual width of the cutting edge at it's finest point.

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Like - this discussion is worth the price admission. cool


If things were as obvious as they initially appear . . . then men would be riding horseback sidesaddle . . . and not women. - Will Rogers
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engineers have equipment that can measure the fineness of secondary & primary bevels to the hundred thousandths. however these machines are not usually affordable to most knifemakers & for fact are'nt even important to knife specifications. i believe the realm in which you are interested lies in the labatories that can weigh a pencil mark on paper or the dimensions of extremely small atoms or molecular particles. not trying to upset you but this fine measurement you desire to understand has no importance in most cutting tools.--cranky72

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I realize that it has no importance in most cutting tools, except maybe for scapels used in delicate surgery, like eyes, and I think lazers are what are most in use now.

When a knife is sharpened, the edge is something like a V, and where the two lines converge are what makes the edge. One difference in the shape of the V would be what some refer to as an appleseed shape, where the sides are rounded until they converge. What I am trying to find out is how broad this spot can be and the knife be considered sharp.

No importance, yes, but I figure that knowing is better than not knowing.

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practice is the best teacher--find some knifemakers & ask them for visits to their shops. maybe watching their operations you can see what prefects sharp edges. as to the sharpest edge find a friend at cal poly tech--possibly the best u.s. engineering institution & make enquiries. other contributors in some forums still say the diamond knife is the sharpest edge in the world. very possibly the answers you seek are not in this area of information.--cranky72


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