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Post by connorclarke on Mar 25, 2017 8:15:24 GMT
From a forging or engineering perspective - why do some blades have both bo-hi starting all the way back, beneath the habaki and some start the grooves an inch or two further down the blade? Can be also to lighten the blade and alter balance as well.
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Post by Robert in California on Mar 28, 2017 12:43:16 GMT
I got a bohi katana and waki for a lighter, quicker (if less powerful) blade and to hear my cuts better (being old and hearing less than when young...due to a mispent youth :-). RinC (but non-bohi is my preference for backyard cutting...my "opponents" (water-filled one gallon soft plastic milk jugs) have combat reflexes even slower than my own...so far, I have won all my duels with them. :-)
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pattyb0009
Member
Getting into antique sabers...
Posts: 1,886
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Post by pattyb0009 on Mar 28, 2017 15:03:18 GMT
Both look just fine to me. I appreciate nohi a tick more because I get to see more of that scrumptious hada without interruption.
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Post by connorclarke on Mar 28, 2017 19:34:25 GMT
Another thing is they can make a blade stiffer. If you have never had a really stiff blade without a bohi and compared it to one's that bend more easily with less force you won't know what I'm talking about.
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Post by randomnobody on Mar 28, 2017 22:32:53 GMT
My blades with bohi have far more flex than my blades without. I don't know where the "bohi stiffening" notion comes from, other than I-beam theory, and these aren't really I-beams...
I'm thinking thickness and taper have a lot more to do with stiffness than bohi...
Of course, that's just my own experience.
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Ifrit
Member
More edgy than a double edge sword
Posts: 3,284
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Post by Ifrit on Mar 28, 2017 22:41:53 GMT
My blades with bohi have far more flex than my blades without. I don't know where the "bohi stiffening" notion comes from, other than I-beam theory, and these aren't really I-beams... I'm thinking thickness and taper have a lot more to do with stiffness than bohi... Of course, that's just my own experience. I second this. Im pretty sure bo-hi dont add stiffness, but i have had plenty of people on reddit insult me for thinking otherwise
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Post by Timo Nieminen on Mar 28, 2017 22:51:23 GMT
My blades with bohi have far more flex than my blades without. I don't know where the "bohi stiffening" notion comes from, other than I-beam theory, and these aren't really I-beams... I'm thinking thickness and taper have a lot more to do with stiffness than bohi... With bohi, the blade can be thicker for the same weight - therefore stiffer. If you don't make it thicker, it won't be stiffer. Cutting a bohi into a blade makes it less stiff (compared to the blade before cutting it). (And that's how I-beams work - an I-beam is less stiff than a solid beam of the same width and thickness, but much, much lighter. For a given weight, you can make it much wider and thicker, and therefore much stiffer.)
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Post by randomnobody on Mar 28, 2017 23:13:41 GMT
Right, that's the theory.
But in my swords, the thicker ones have bohi...and flex more. So it's an oddity in my perception.
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Post by Timo Nieminen on Mar 28, 2017 23:36:08 GMT
If only a little bit thicker, they can be more flexible. The stiffness per unit length is also affected by width. Then, how easy it is to bend the whole sword (as opposed to stiffness per unit length) depends on the length of the blade (more length gives you more leverage to bend it, and the bending is distributed over more blade) and how the stiffness varies along the blade.
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Post by connorclarke on Mar 29, 2017 0:08:25 GMT
I disagree. I have blades that had more flex that were thick and had fullers but bent easier. After removing alot of niku from the blade the purpose of the fullers kicked in and the blades became stiffer, due to the relative amount of metal becoming less to the depth of the bohi.
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Post by vermithrax on Mar 29, 2017 0:32:54 GMT
Had no idea this thread would be so fun, great interaction.
I still rule out Bo-Hi blades unless no choice.
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Ifrit
Member
More edgy than a double edge sword
Posts: 3,284
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Post by Ifrit on Mar 29, 2017 0:55:08 GMT
I disagree. I have blades that had more flex that were thick and had fullers but bent easier. After removing alot of niku from the blade the purpose of the fullers kicked in and the blades became stiffer, due to the relative amount of metal becoming less to the depth of the bohi. I doubt thats the purposs of the fullers. Pretty sure the idea is to remove material while retaining stiffness, not to improve stiffness.
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Post by randomnobody on Mar 29, 2017 1:01:02 GMT
I just remembered, when I was working with James Raw (via Bill Williams), many years ago, I asked about adding a naginata-hi (naginata-naoshi style wakizashi) and was denied. James, at the time at least, was not confident in his ability to make bohi well, so as an alternative, he offered to taper the shinogi-ji more steeply, providing the same weight-reducing effect.
I'm curious if the more diamond profile would have been more or less stiff. Considering the majority of the blade already has the high shinogi, and is so short and fat I can't even try to bend it, I'm not even sure it matters...
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Post by seriouslee on Mar 29, 2017 1:10:48 GMT
sparkyswordscience.blogspot.com/2013/11/why-fuller-doesnt-make-sword-stiffer.htmlFascinating even if you skip the math. "Hopefully I've convinced you: Fullers do not make swords stiffer, in fact they do the opposite. Their greater purpose is to make swords lighter." "About those hammered fullers So the I-beam profile created by a fuller isn't responsible for any increase in stiffness over an equivalently sized solid section. But what if the fuller wasn't created by removing material, but rather by moving material around?" Which is how I know them to be applied. My blade with two bo-hi weighs the same as the blade with none. In fact, an ounce heavier and the blade is an inch longer.
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Ifrit
Member
More edgy than a double edge sword
Posts: 3,284
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Post by Ifrit on Mar 29, 2017 1:15:26 GMT
sparkyswordscience.blogspot.com/2013/11/why-fuller-doesnt-make-sword-stiffer.htmlFascinating even if you skip the math. "Hopefully I've convinced you: Fullers do not make swords stiffer, in fact they do the opposite. Their greater purpose is to make swords lighter." "About those hammered fullers So the I-beam profile created by a fuller isn't responsible for any increase in stiffness over an equivalently sized solid section. But what if the fuller wasn't created by removing material, but rather by moving material around?" Which is how I know them to be applied. My blade with two bo-hi weighs the same as the blade with none. In fact, an ounce heavier and the blade is an inch longer. Thank you sir. I needed that study. Gotta book mark that for reddit arguments.
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Post by Timo Nieminen on Mar 29, 2017 1:16:26 GMT
I disagree. I have blades that had more flex that were thick and had fullers but bent easier. After removing alot of niku from the blade the purpose of the fullers kicked in and the blades became stiffer, due to the relative amount of metal becoming less to the depth of the bohi. I'm not sure what you mean by your description. Can you draw a picture of the cross-sections you mean? The basic principle is simply that the more steel you have further from the centre plane, the stiffer the blade is. See first equation on en.wikipedia.org/wiki/Second_moment_of_area and in particular, note the rho^2 (rho = distance from the centre plane). So there's more to it than pure thickness (e.g., a hex-section blade is stiffer than diamond-section for the same thickness - for a simple case, from en.wikipedia.org/wiki/List_of_second_moments_of_area we see that an elliptical section only has 59% the stiffness of a rectangular section of the same thickness and width).
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Post by vermithrax on Mar 29, 2017 1:29:48 GMT
I always thought the grooves in blades were meant to start capillary blood loss via the cut. Dunno.
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Ifrit
Member
More edgy than a double edge sword
Posts: 3,284
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Post by Ifrit on Mar 29, 2017 1:56:25 GMT
I always thought the grooves in blades were meant to start capillary blood loss via the cut. Dunno. Naw that is a myth. I think that myth started because certain knives that doctors have had this feature. As usual, i could be wrong My bo-hi ronin has a lot more presence in the hand than my solid bodied blade does though for sure. I always assumed it was to bring the balance towards the hilt
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Post by connorclarke on Mar 29, 2017 2:39:03 GMT
I disagree. I have blades that had more flex that were thick and had fullers but bent easier. After removing alot of niku from the blade the purpose of the fullers kicked in and the blades became stiffer, due to the relative amount of metal becoming less to the depth of the bohi. I'm not sure what you mean by your description. Can you draw a picture of the cross-sections you mean? The basic principle is simply that the more steel you have further from the centre plane, the stiffer the blade is. See first equation on en.wikipedia.org/wiki/Second_moment_of_area and in particular, note the rho^2 (rho = distance from the centre plane). So there's more to it than pure thickness (e.g., a hex-section blade is stiffer than diamond-section for the same thickness - for a simple case, from en.wikipedia.org/wiki/List_of_second_moments_of_area we see that an elliptical section only has 59% the stiffness of a rectangular section of the same thickness and width). I'm trying to explain that in my experience and reading about fullers on nihonto by Japanese Smith's in books that they can add stiffness. I found that this principle seems to work best on thinner or properly proportioned blades relative to how well placed and deep the bohi is cut. Contrarily the rule seems to be the opposite on thicker blades and shallow cut bohi which seems to increase ease of flex instead which you seem to know already as stated.
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Post by Croccifixio on Mar 29, 2017 2:49:19 GMT
The myth was propagated by the US army putting it in their manuals about bayonets and knives :P
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