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Who Makes the Sharpest Knife?

Discussion in 'Non-Firearm Weapons' started by stressed, Oct 26, 2013.

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  1. stressed

    stressed Member

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    Interesting.

    Who makes the hardest, sharpest knife available? That model?
     
  2. ugaarguy

    ugaarguy Moderator Staff Member

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    I moved this here from the Chinese knife discussion thread because it's a great question, and really deserves its own thread to discuss.

    I'll start things out. Often, the sharpest knife isn't the hardest. Carbides are the predominant factor in making a knife hard. Yet, if there's too much carbon in the alloy the carbides tend to be large. These large carbides actually result in reduced edge stability, which prevents the blade from being sharpened to as an acute angle. Sandvik 13C26 is widely used in cutlery, and it's a near identical copy of Uddeholm AEB-L. AEB-L was originally developed as a razor blade steel, and it's really more of a medium carbon steel. However, the low carbon to chromium ratio in the alloy results in a very fine grain structure. This fine grain structure allows AEB-L to be polished to a very fine, very acute edge.

    The counter to this is that a harder steel with larger carbides will typically hold its edge longer than a softer, finer grained steel. Such steels will typically take a pretty sharp working edge, and retain that edge for a long time.

    Another factor is that the higher the hardness a steel is heat treated to, the more brittle it becomes. This results in a blade that isn't very tough or durable.

    That's as much amateur metallurgy as I can muster at this hour, so I'll leave this to the experts to elaborate on.
     
  3. Cryogaijin

    Cryogaijin Member

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    Oversimplified answer: virtually any zirconium blades. There are reasons you need diamond sharpening tools to sharpen them.

    OTOH they're useless outside a very narrow area of use: too brittle. Torque the blade at all and it will snap. I've snapped Zirconium paring knives dicing potatos. Still for what they do they're much sharper and easier to maintain than metal knives, right up until *crack*
     
  4. hso

    hso Moderator Staff Member

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    "Sharpest" isn't a term easily understood. Sharp for what cutting task can be different. Soft materials like meat or foam cut differently than rope or some fabrics. Fine vs. toothy edges cut those materials differently and are therefore "sharp" differently. Toothy is "sharpest" on materials that fine wouldn't be and vice/versa.

    Hard isn't what most people mean either. Hard and wear resistant and tough are all terms people use with "hard" being said when they mean wear resistant or even sometimes tough. Hardness is simply the resistance to indentation/deformation and is easy to test with a Rockwell Hardness tester, but that doesn't mean the material is resistant to wear and will "hold an edge" for a long time. Too hard and the edges chip and "sharpness" is lost. Toughness also isn't hardness, but it is a characteristic sought in knives to resist twisting/bending repeatedly without breaking. There's commonly an inverse relationship between hardness and toughness. Resistance to wear is often the performance characteristic that people commonly seek since it equates well to edge holding.

    It is better to specify the performance you want to see. Cuts rope or meat, holds and edge well or easy to sharpen, keen or toothy, resists breakage.
     
    Last edited: Oct 26, 2013
  5. lobo9er

    lobo9er Member

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    There is no answer. Most knives NIB from the factory are not as "sharp" as they have the potential to be. Which knives consistently come sharp out of the box from factory might be a better question, but doesn't help conclude which is a better knife.
    I have a Ozark MTN walmart knife that I just sharpened up that is a razor right now but it doesn't make it a better knife than the BK 14 I use to make kindling by the fire because it isn't currently hair popping. I would imagine the throw away razors in box cutters are as sharp or sharper than production blades but it doesn't mean thats what you want camping.

    And as HSO said harder isn't always better.
     
    Last edited: Oct 26, 2013
  6. mole

    mole Member

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    Hardest and sharpest? A flintknapper. It'll be a small, brittle blade though since to have only "one" edge you'll be stuck with a large flake.
     
  7. allaroundhunter

    allaroundhunter Member

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    Little (general) lesson in materials.

    The harder a material is, the harder it is to machine. In this case, sharpen.

    The harder a material is, the less ductile and more brittle it is.


    There is always trade-off, so knowing what you want out of a knife will help you determine what material you should be looking for.
     
  8. Shanghai McCoy

    Shanghai McCoy Member

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    The sharpest that I have seen straight from the factory are the Mora blades.
     
  9. Sam Cade

    Sam Cade Member

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    That is a great example of the confluence of fine grained steel, aggressive edge geometry and a thin blade.
     
  10. hso

    hso Moderator Staff Member

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    Sharpest, as in cut you the easiest, I ever handled were the original Blackjack convex edge knives and the Microtechs. A buddy sliced his fingerprint off so finely with a BJK that it didn't bleed.
     
  11. GLOOB

    GLOOB Member

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    I can get a pretty sharp edge on anything. And I don't own any expensive knifes. But...

    The sharpest knife I have, by far, is a Mora woodcarving knife. It's sharper than my straight razor. The laminated carbon steel is Rockwell 61, or so.

    My Svord Peasant turned out incredibly sharp, once the secondary bevel was polished up a hair. It think it takes a keener edge than most of my regular carbon steel Moras. I don't know the hardness.

    My Mora #1 takes a keener edge than my other plain carbon Moras. It must have gotten a different heat treat, or whatnot. I have shaved my face with it.

    My woodcarving knife has the original scandi edge. My other Moras have been reground to full convex. And the Peasant has the original crude saber grind on it; the secondary is fairly obtuse. I think the absolute sharpness of the edge is limited by the steels rather than the grinds, though.
     
    Last edited: Oct 26, 2013
  12. snapshot762

    snapshot762 Member

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    The sharpest knife (out of the box) i have ever owned was a Chris Reeve one piece hollow handled SableIV.
     
  13. theboyscout

    theboyscout Member

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    I truly like MORA knives, they are an inexpensive knife that is tough as can be.

    http://moraofsweden.com/knife-care-1.0.263.2

    Knife steels contain between 0.4 to 0.7% Carbon and between 13 and 18% Chromium. Carbon is necessary to make the steel hardenable and Chromium to is present to prevent corrosion ie rust. In general it can be said that Carbon contents below 0.5% are not to be recommended for professional usage since it is not possible to achieve sufficient hardness. When grinding knives used for the finishing operations, the total grinding angle should be around 25°. If this angle is less, whilst the knife will be extremely sharp, it will also mean that the knife condition will also be very sensitive since the extreme knife edge point will easily be folded over when coming in contact with harder objects. Boning knives on the other hand are ground to higher angle, approx. 35° and thereby up to tougher usage and heavier work on the knife edge even though this is at the expense of a somewhat higher cutting resistance
     
  14. Deltaboy1984

    Deltaboy1984 Member

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    Same here .
     
  15. clearcut

    clearcut Member

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    flaked obsidian I think is the sharpest but you have to re flake it often.
    CC
     
  16. hso

    hso Moderator Staff Member

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    Not that this is what I think we're actaully asking, but ultramicrotomes are probably the sharpest, but they do one thing and they're not tough. The concave glass or diamond blades are used depending upon material being sectioned.
     
    Last edited: Oct 29, 2013
  17. Bikewer

    Bikewer Member

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    The folks mentioning obsidian have a point. You can only get steel so sharp... Has to do with the micro structure of the material.
    If you look at a very sharp edge under an electron microscope, it looks pretty much like a saw. Rather jagged, but all the little "jags" are in the same direction.
    When such an edge gets dull, the little jags are all over the place.

    Obsidian (or other glass items) fractures down to a single molecule. You can't really get any sharper than that practically, although engineers have produced a "needle" point down to a single atom... Using a scanning-tunneling electron microscope that allows the manipulation of single atoms.

    As noted there's a fine line between ultimate sharpness and durability.
     
  18. lobo9er

    lobo9er Member

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    good post bikewer. interesting
     
  19. Slamfire

    Slamfire Member

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    I saw a History Channel program on knives and they were going down the Cutco knife production line. At the end was a sharpness tester, looked to be an industrial piece of equipment. Used a special type of paper and the knife was put in a fixture and it was determined how many cuts the edge could make.

    So this was a standardized way of testing sharpeness. Don’t know where you could find a tester and expect it would cost $$$. Maybe $$,$$$.00

    The basic problem with all of the opinions you find on the web, on who makes the sharpest knives, is a lack of an agreed on standard test to compare edges and edge retention. Some people cut cardboard, which is a severe test in my opinion, others cut rope, some cut bricks and complain when the knife fails.
     
  20. hso

    hso Moderator Staff Member

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    There are agreed upon standards for testing "sharpness", just not commonly known outside of knife websites.

    Informally, those standards are - draw cut of newsprint or toilet paper without ripping, how many push cuts of 1/2" sisal rope before the edge dulls and tears the paper, how many inches of draw cuts of corrugated cardboard before the edge dulls and tears the paper, how many lays of free hanging 1" sisal rope can be cut with one pass, back to nontearing cuts on newsprint/toilet paper.

    Formally, there are machines to achieve the same thing and make the counts.


    Then there are the ABS competition requirements - http://www.youtube.com/watch?v=GhlL1wLuZxw
     
    Last edited: Oct 31, 2013
  21. ugaarguy

    ugaarguy Moderator Staff Member

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    Slamfire, the machine you're referring to is a CATRA Knife & Blade Cutting Test Machine. They're no doubt incredibly expensive because CATRA states there are only 32 in use in the world. CATRA also makes a sharpness tester which measures pure sharpness rather than cutting performance with a wear factor.
     
  22. hso

    hso Moderator Staff Member

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  23. GLOOB

    GLOOB Member

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    As far as hardest, Ragweed Forge sells Ultra High Carbon Roselli knife blades with HRC 64-66. That's pretty darn hard. Especially considering they're scandi ground, sharpening could take some time. They recommend diamond sharpening stones.
     
  24. Phaedrus/69

    Phaedrus/69 Member

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    Judging a knife by the OOtB edge is like judging a car by how much gas is in the tank when you buy it. You would expect (or at least hope) that the knife is sharp OOTB (out of the box) but it won't be nearly as sharp as it can get. This is because it takes a lot of work to get a truly superior edge, and it can't be completely automated. So a human has to do a lot of hand/hand-machine work to do it, and that costs money. And there's a point of diminishing returns to consider; how much extra sharpness is the worth the extra money? How many will appreciate it?

    Hardness with knife blades is generally expressed a number on the Rockwell scale. This number isn't linear; that is to say, 51 RC isn't 2% harder than 50 RC, it's a magnitude harder. At any rate, hardness has little to do with toughness. For example a glass or ceramic knife will be very, very hard- harder than most steels can get. But it won't be tough. You can easily chip the edge of a glass knife even though it's very hard. So you have to look at toughness, but edge stability is another factor. Many of the attributes we like to have in a knife are mutually exclusive. Raising one attribute often lowers another.

    Hard knives may be a little harder to sharpen but not necessarily. Super Aogomi is often hardened to around 65 RC but it's relatively easy to sharpen. Steels with things that make it tougher, like vanadium, make the knife harder to sharpen but not physically harder. In a sense steel is little like concrete, or peanut brittle. The steel is like the concrete while the vanadium carbides are like the aggregate. Put another way the carbides are like the peanuts.

    If you're asking which knives are the sharpest OOTB that's also tricky. Sharp can mean a lot of things. A polished edge may shave hair well and push cut so you'll call it very sharp...until you try to cut rope with it and it won't cut well. Likewise a knife that will rip through cardboard boxes all day seems sharp until you go to shave hair- then it's just ripping hairs out.

    But as far as OOTB sharpness goes, Mora knives are usually very, very sharp. There's a little variation but you have maybe a 95% chance of getting a Mora that will be very very sharp. Bark River knives are pretty sharp OOTB, too. If you get one of the ones made in Taiwan (not China) the SOG Field Pup is sharp OOTB. And I'd say virtually every Spyderco I've ever seen was quite sharp OOTB.
     
  25. hso

    hso Moderator Staff Member

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    The Diamond Blade folks get remarkable sharpness and durability out of their process.
     
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