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Thread: How sharp is sharp?

  1. #1
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    How sharp is sharp?

    I clearly do not use edged weapons for combat, but I suspect that for real use - battle-field type use - there is such a thing as "too sharp". I suspect that an extremely sharp edged weapon is probably more likely to be impacted by damaging contact, resulting in edge damage, making the weapon less effective at cutting. (essentially, the finer an edge, the greater the drop in cutting effectiveness with edge damage) I don't know how this impacts real-life sharpness.

    That said, I must say I am amazed at how sharp my Paul Chen Orchid katana and wakizashi are.

    I expected that I could hold a piece of paper and be able to cut through the paper with the blades. I actually cut through the long way with absolutely no bend or tears - just straight through - I was pleased, but not overly surprised. But, I was curious how much force I needed to cut a piece of paper.

    I had no problem _pushing_ a piece of paper across the blade and cutting the paper - not moving the sword, just the paper. I curved the paper slightly to hold it stiff, then ran it straight against the blade, raising my hand about 3 inches as I did, stopping my hand about 4 inches from the edge. The katana cut about 4 inches through the paper, with a straight, clean cut. The wakizashi cut just shy of 4 inches, with a slight bend and tear in the paper at the end of the cut. I thought both cut incredibly easily. I tried the same cut with a razor blade, and my exacto knife. Neither could duplicate the cut - at all - the paper bent witih no cut. I tried the same cut with my Henckels Santoku - it started the cut, about an inch, then the paper bent, crumpled, and tore.

    This made me more curious, so I tried some experiments. I dropped a piece of plain white printer paper - and in mid-air - cut straight through with both the katana and wakizashi. When I hit the paper with the Henckel, it just smacked the paper away - I do not know how much of this is form - perhaps I just executed the cut differently with the knife than I did with the swords.

    I know the "drop the silk on the blade" test is all fantasy, but I wondered about what it would take to cut a light cloth. I dropped a silk scarf (old magic kit, cheap silk, but light) and attempt a horizontal, one-handed cut with both the katana and the wakizashi. Neither can cut the "floating silk" scarf. I figure that means the blade is just pushing the silk out of the way - not enough resistance at the blade edge. How do I increase the resistance? I wet the silk scarf lightly (I mist the scarf slightly with a spray bottle), to add weight and no cutting resistance. I repeat the cut with the damp silk. Both the katana and wakizashi sail right through the silk, and the silk drops almost straight (almost) to the floor. The silk doesn't even look like it was cut - it just looks like it was formed that way - there are no loose threads are frayed edges. I repeat the test with the Henckels Santoku, and again, I effectively just bat the silk away with the blade edge (again, understanding that there may be form differences between sword and knife use - but the consistency of my results tend to indicate otherwise). I suspect, if nothing else, that the effectiveness of the cuts indicate decent form.

    This made me want to do some real testing on how much weight it takes to make a real cut on various subject matters - but that is more energy than I want to spend right now.

    I can use my Henckels Santoku to cut translucent layers of tomato maybe 1/16 of an inch thick - and informal test results indicate that the katana and wakizashi are even sharper than the Santoku? I have to assume that this is an abberation isn't it? I see many warnings that "blades are sharp!", but are production katanas normally _this_ sharp?

  2. #2
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    wow...

    This topic could get a whole lot of talk.

    And it already has....

    You should definantly read the:

    "Cutting ability in swords, a primer"

    This thread was started by Tinker (Michael Tinker Pierce) and can be found via search very easily. I think it does the best possible job of getting into the heart of the questions you raised in your post.

    End of the day? Damage to the blade's edge is about edge geometry, edge hardness, blade flex, cutting arc, tip speed, edge alignment, target hardness, target density, etc.....

    Get my point? There is no simple answer. Some blades were very sharp for their applications, some were not as sharp.

    As for your question on production katana....yes, in my experience they have been frighteningly sharp. Even my PC PK (which is my 'beater' kat) is so darn sharp I am almost scared of its edge.

    My ATrim does not have that razor sharp feel to it...but it manages to cut like a laser anyway. That was a lesson for me in the difference between what you need on a knife edge and what you need on a sword's edge. A sword does not need to be razor sharp to do its job.

    Hope that helped.

    chris.
    "The limits of tyrants
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    of those whom they suppress."
    -Frederick Douglass

    "Quality. There is hardly anything in the world that some men cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey."
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  3. #3
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    Re: How sharp is sharp?

    Originally posted by Jon Heimerl
    That said, I must say I am amazed at how sharp my Paul Chen Orchid katana and wakizashi are.
    I've an ancient tool made to cut dressed leather to make horse
    harness and saddles. It was polished and sharpened by my Senpai, just for fun.
    It is the closest thing to lightsaber I've handled till now, but it is so hopelessly fragile. It wasn't intended for battle.
    The right is in the middle.
    Please forgive my english.

  4. #4
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    Talking Rule of Thumb....

    If you can cut your finger by lightly sliding it along the blades edge, then its too sharp. Blades that sharp should only be used to shave with.
    I'm lost---- I've gone to look for myself. If I should return before I get back, please ask me to wait.

    If you think education is expensive, try ignorance.

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  5. #5
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    Do you test this???

  6. #6
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    Originally posted by Van Rei
    Do you test this???
    Everyone here has, mostly by accident of lack of commen sense.
    I'm lost---- I've gone to look for myself. If I should return before I get back, please ask me to wait.

    If you think education is expensive, try ignorance.

    I work for Keyser Söze.

  7. #7
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    In another thread, someone asked me how they could sharpen their KC bare blade. The KC is a katana blade, in 220 grit finish.

    Here was my response, I think it might be useful in this thread, for those wishing to restore the cutting edge of their katana that are not nice enough to warrant a full polish. This is for 'working' blades only. If you try this with a Nihon-to, someone should smack you with a wet glove.

    ****

    Never ever use a grinder, buffer, or any other buffing/sharpening device that generates heat on a blade that has been heat treated. This goes for katana and western blades as well. If you raise the steel's temp to 400-500 degrees, even just along the thin edge, you will ruin the hardening.

    Here is what you should do, unless you want to try a full polish.

    Your KC blade is only in 220 grit finish. It is probably already sharp enough to be an effective sword. Swords do NOT need to be the same kind of sharp as a knife, in fact it can be bad for them in certain cases.

    Go get yourself 400, 600, and 800 grit sandpaper. Get the good 3M stuff, no cheap imitations. You can find them at any fiberglass supply, or autobody supply shop. They are not expensive.

    Tear off postage sized pieces of the paper starting at 400, and with water, run them along the edge with your finger CAREFULLY. You will want to have the pressure at a 30 degree (or therabouts) angle to preserve the geometry already there. Run them down the edge in long strokes lengthwise down the blade. Make passes with 400 grit until you feel the edge smooth out (you will feel it if you pay close attention). One of those squares is only good for about 5 passes, so you will use a few. Repeat this all the way up to 800 grit, and your blade will be as sharp as the devil himself.

    This is basically what I did when I was finishing the hybrid polish on my KC blade, I spent time at each grit trueing the edge in this manner, and by the time I got to 800 it was scary sharp.

    The important thing, is that this way, you will not ruin the geometry already in place, you will just hone the edge to a fine surface.

    BE CAREFUL, DO NOT CUT YOURSELF!!!

    I can't stress this enough, you must pay attention, turn the TV and music off. Focus on what you are doing, or you can get cut.

    With the 3M paper I never had it cut through the paper, partly because it is good paper, and mostly because my angle was correct with respect to the edge. You should be able to do this with a piece of newspaper and not cut through, if your pressure and angle are correct.

    A consequence of this method, is that your edge will be nearly mirror shiny afterward. If you did this to the whole blade, you would be on your way to a beginner's hybrid polish like mine.

    ****

    And a picture (or two) for reference.

    Best.

    Chris.
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    "The limits of tyrants
    are prescribed by the endurance
    of those whom they suppress."
    -Frederick Douglass

    "Quality. There is hardly anything in the world that some men cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey."
    -John Ruskin

    www.inaharabladecrafts.com

  8. #8
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    And here is what happens if you use a grinder on a katana, even if you do not ruin it from the heat generated.....
    Attached Images Attached Images  
    "The limits of tyrants
    are prescribed by the endurance
    of those whom they suppress."
    -Frederick Douglass

    "Quality. There is hardly anything in the world that some men cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey."
    -John Ruskin

    www.inaharabladecrafts.com

  9. #9
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    "On Knives and western blades it is fine" is not a true statement.

    On *some* knives and *some* western blades a secondary bevel is used.

    Just as it would not be correct to say "all katanas are made with stick tangs" cause *some* are made that way.

    Thomas

  10. #10
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    Hmmm....

    I did not mean to pass an unfair, or inaccurate statement...but I have never owned a knife without a bevel, and I have owned nearly 50 knives of quality.

    I agree that there are some knives out there without a bevel, but is is not fair to say that when talking of knives in general, a bevel is something permissible?

    As for western blades....I have also never seen one without some kind of bevel to the edge. Then again, I have not seen or handled nearly as many western swords as knives.

    Can you please educate me on what styles of western blades it is considered inappropriate to have a bevel? I am genuinely interested.

    As for the rat-tail tang, I have no comment. We both know that statement was reactionary. I am sorry if I offended you.

    Sincerely

    Chris.
    "The limits of tyrants
    are prescribed by the endurance
    of those whom they suppress."
    -Frederick Douglass

    "Quality. There is hardly anything in the world that some men cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey."
    -John Ruskin

    www.inaharabladecrafts.com

  11. #11
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    sharp

    hey


    apparentely katanas were meant to be able to cut through a human hair, like just putting the hair on the edge. hmmm....

  12. #12
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    Re: sharp

    Originally posted by John Mankey
    hey


    apparentely katanas were meant to be able to cut through a human hair, like just putting the hair on the edge. hmmm....
    Say's who? There is no reason for any sword to be that sharp. The matainence costs would kill you.
    I'm lost---- I've gone to look for myself. If I should return before I get back, please ask me to wait.

    If you think education is expensive, try ignorance.

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  13. #13
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    I just assumed that was a joke.

    Mr. Mankey, if you were not joking, there is a whole world of information waiting for you in the *stickies* and *search* funcitons of this forum. And it is all free, you can't beat that.

    Any blade that was hair splitting sharp would be devastated when it encountered armor, or even bone for that matter.

    A search for 'niku' will yield many many sources of information about the relationship between sharpness and durability in Japanese blades.

    Best.

    Chris.
    "The limits of tyrants
    are prescribed by the endurance
    of those whom they suppress."
    -Frederick Douglass

    "Quality. There is hardly anything in the world that some men cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey."
    -John Ruskin

    www.inaharabladecrafts.com

  14. #14
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    Not to leave out Western blades....

    Please see this interesting thread:

    http://forums.swordforum.com/showthr...threadid=46235

    It contains a discussion of primary, secondary bevels on western blades, and the use of the 'appleseed' and other curved bevels on western blades.

    It seems that both the curved bevel and the secondary (straight) bevel were used widely throughout many differnt periods and places in the history of western swords.

    It seems fairly clear that some kind of bevel was on nearly every western cutting blade that saw wide use. Regardless of whether you were talking about curved or straight secondary bevel characteristics, the bevel was very very common.

    Best.

    chris.
    "The limits of tyrants
    are prescribed by the endurance
    of those whom they suppress."
    -Frederick Douglass

    "Quality. There is hardly anything in the world that some men cannot make a little worse and sell a little cheaper, and the people who consider price only are this man's lawful prey."
    -John Ruskin

    www.inaharabladecrafts.com

  15. #15
    FYI, traditional scandinavian knives have no secondary bevels. You can search for "puukko", which is the best known type. I use one of these for wood working:
    http://www.knifecenter.com/kc_new/st...tml?s=FINNM571

    Funny how a plastic-handled hardware store grade knife has the best edge I've ever seen... It's even differentially hardened and has a hamon if you look at it right (IIRC the edge is 62RC, the spine in the 40s).

    The convex appleseed or lenticular shape is the same thing as "niku" in Japanese swords... so I wouldn't call it a bevel either. Bevel implies an angular transition from one distinct surface to another.
    Iikka Keranen

  16. #16
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    Originally posted by I. Keranen

    Funny how a plastic-handled hardware store grade knife has the best edge I've ever seen... It's even differentially hardened and has a hamon if you look at it right (IIRC the edge is 62RC, the spine in the 40s).

    The convex appleseed or lenticular shape is the same thing as "niku" in Japanese swords... so I wouldn't call it a bevel either. Bevel implies an angular transition from one distinct surface to another.
    Not sure how that would make a good knife edge? Any kind of knife with "niku" would make it more difficult to cut with, so i'm not certain why they would do that less for some asthetic reasons. Could you provide more feedback. Thanks.
    I'm lost---- I've gone to look for myself. If I should return before I get back, please ask me to wait.

    If you think education is expensive, try ignorance.

    I work for Keyser Söze.

  17. #17
    Angus Trim is offline Moderator
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    Originally posted by I. Keranen
    Bevel implies an angular transition from one distinct surface to another.
    That's true, but...........

    Making swords for a living has made me acutely aware of edge geometry. And how hte edge transitions to the main bevel. In a very basic way, all of the antique sword blades fit into one of two catagories as far as edge geometry goes.....

    1.The main bevels come together to form the edge

    2. There is a secondary edge bevel.....

    This later breaks down a bit too.....
    1. The edge bevel is flat, and there is a smooth transition into the main bevel
    2. The edge is convex and there is a smooth transition into hte main bevel
    3. There is a sharp transition between the main bevel and the edge.

    The main bevels of the kat ussually are a bit convex, this is the "niku". Much of the main bevel, not just some convexity at the edge.

    Other than kats, I've seen two antique gian where the edge is the intersection of the main bevels, and an antique baskethilt backsword.

    The best antiques I've seen have a bit of secondary beveling, ussually very well blended in. You can call it anything you want, but functionally its a secondary bevel.

    Sometimes a secondary bevel is rather obvious. Later military sabers sometimes have this, and I've seen older antiques that have this too.........
    For Good or Ill......

    What Comes Around Goes Around.....
    and

    You Reap What You Sow...

  18. #18
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    Re: Re: sharp

    Originally posted by D. Opheim
    Say's who? There is no reason for any sword to be that sharp. The matainence costs would kill you.
    ...but it'd be cool...

  19. #19
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    Re: Re: Re: sharp

    Originally posted by Van Rei
    ...but it'd be cool...
    Touche'
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  20. #20
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    Seriously, though... I'm a newb to blade geometry (and I hated regular geometry... if only we had learned about swords then...). Is the bevel like a second blade angle?

  21. #21
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    Originally posted by Van Rei


    Seriously, though... I'm a newb to blade geometry (and I hated regular geometry... if only we had learned about swords then...). Is the bevel like a second blade angle?
    More like a secondary edge to the blade. A strait "no frills" blade edge is far more likely to be damaged. If the very end of the edge is slightly angled inward from both sides (the secondary bevel), then it greatly decreases this risk. This is also referred to edge retention; or the ability to retain the edge. I'm not familiar with all the specific details, but I know it works some how.


    It should be noted though that all geometry is not created equel. Different types of blades will demand different types of geometries. Some will work better than others, but also could increase the risk of damage. The secondary bevel in my opinion is much like a car bumper. Large or small, hidden or obvious, it helps protect what its attached too. Mostly.
    Last edited by D. Opheim; 02-02-2005 at 09:23 PM.
    I'm lost---- I've gone to look for myself. If I should return before I get back, please ask me to wait.

    If you think education is expensive, try ignorance.

    I work for Keyser Söze.

  22. #22
    I wouldn't say that the puukko has niku.
    The main bevel is flat, granted the only ones I have are by Frosts. I can't really tell what the high end, or even $50 ones have from pictures. They look flat.

    Does it make a good knife edge? That depends on end use as you know, but I like it. This design makes for a fragile edge. One in particular I have is very prone to chipping on tough material, it is very hard, but can be made so incredibly sharp I wish I could measure its edge width. How big is a martensite crystal anyway, in microns?

  23. #23
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    Originally posted by D. Opheim
    (cut)
    I think I get it. Thanks for the info!

  24. #24
    Oh, I didn't mean the Scandi knives have "niku". That bit was about the similarities in the geometry of western lenticular section swords and Japanese swords, and at least partly erroneous as Gus pointed out Though I think I've seen some diagrams of western sword cross-sections that were in fact lenticular with the whole primary bevel being convex.

    On these knives the grind is flat, like you'd see in a diamond-section sword with no secondary bevels, or a katana with no niku, or even a chisel. It makes the edge really sharp and it cuts with less pressure than knives with secondary bevels (like the OP experienced with his swords).

    edit: oops, I guess someone already answered this.

    Originally posted by D. Opheim
    Not sure how that would make a good knife edge? Any kind of knife with "niku" would make it more difficult to cut with, so i'm not certain why they would do that less for some asthetic reasons. Could you provide more feedback. Thanks.
    Iikka Keranen

  25. #25
    Humm, how sharp is enough for a Katana? Well, first the entire blade of Katana doesn't have to be all sharp, as long as the top 1/3 of the blade is sharp enough is good. You won't use the buttom part of ha to do the actually cutting, all cuts are done by the top 1/3 of the blade (that's why many katana don't shapen the part of ha near habaki). Also, a Katana doesn't have to be razor sharp, it certainly doesn't have to be able to shave hairs. A katana can be made sharper by reducing the niku and the thickness of the blade so the angle of force gets narrior. But I still recommant a thicker blade with at least some niku, because those blade without any niku tend to dull faster, and the blade structure are much weaker for those blades that doesn't have niku.

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