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Measurements for kasane?


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#1 mas4t0

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Posted 14 January 2020 - 08:13 PM

Are there any commonalities in the thickness of blades at the mune and the shinogi?

 

Is there some consistency within schools, or is it rather idiosyncratic to each blade?


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Mark H

#2 Ken-Hawaii

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Posted 15 January 2020 - 02:50 AM

That's a more complicated question than you might realize, Mark. In general, blade thicknesses in all dimensions increased in times of battle. Check out a Nanbukucho blade next to a Kamakura to see how different they look. You can blame the Mongols for scaring the crap out of the Shogunate, because the slim, elegant Japanese swords broke on Mongol armor!

 

The height/thickness of the shinogi, on the other hand, is much more idiosyncratic to particular schools. In general, older Yamato blades have a fairly-thin shinogi, for example.


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#3 mas4t0

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Posted 15 January 2020 - 07:06 PM

Hi Ken,

Thank you for the information.

I'm trying to get a grasp on the geometry.

While the measurements would be different for each blade, is there some consistency in the proportions of the cross section? Would you say that in response to their experience during the Mongol invasion that the blades were scaled up proportionally in all dimensions, or that there was a transition to a more hexagonal cross section (as shown in the leftmost diagram) which I believe would make the blade stronger in torsion and shear?

 

If we ignore niku, and consider a straight line directly from the shinogi to the ha, is there any consistency in the angle? I realise it would be different for hira zukuri, shinogi zukuri and shobu zukuri; but would they be relatively similar (within a few degrees) within the same category? Would you ever see as in the bottom image, where the edge angle is the same across different geometries?

 

Artboard 312 (1).jpg

 

Thank you.

Mark


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Mark H

#4 Austus

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Posted 15 January 2020 - 09:26 PM

That's an interesting question, Mark; and I hope you get a lot of responses to it. 

But why ignore niku?  That's the key to the cutting dynamics; and without it, you're probably not looking at a Nihonto. Those cross sections look more like the Chinese backyard cutters that don't have to take into account the conditions that a true sword will face. Without niku, there's no support for the edge; it will curl, or worse. There's also a issue called drag; which has something to say in the shinogi and mune design. As posed, this question sounds like one that would be posed to a polisher. 

About the edge angle... is there any perfect one? That's also influenced by the niku, and the battle applications. 

Don't get me wrong, I love this geometry stuff!   Blade design is absolutely fascinating.


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Austus M.


#5 mas4t0

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Posted 15 January 2020 - 09:41 PM

That's an interesting question, Mark; and I hope you get a lot of responses to it.
But why ignore niku? That's the key to the cutting dynamics; and without it, you're probably not looking at a Nihonto. Those cross sections look more like the Chinese backyard cutters that don't have to take into account the conditions that a true sword will face. Without niku, there's no support for the edge; it will curl, or worse. There's also a issue called drag; which has something to say in the shinogi and mune design. As posed, this question sounds like one that would be posed to a polisher.
About the edge angle... is there any perfect one? That's also influenced by the niku, and the battle applications.
Don't get me wrong, I love this geometry stuff! Blade design is absolutely fascinating.


Hi Austus,

I'm not meaning to truly consider blades without niku, but trying to simplify the geometry for the moment so that I can understand the basic angles involved and the nature of the cross section.

With niku, we have a convex edge with varying angles as we transition from the ha to the shinogi. I would consider the angle (without niku) to be the primary angle and the niku to be a convexity applied on it (from a geometric perspective).

I'm also presuming (quite likely incorrectly) that the effect of healthy niku should be somewhat systemic, and proportional to the angle 'θ' shown above; therefore for the sake of comparison we can disregard it.

With niku it gets very complicated. This way, all I need to take account of is the thickness at the shinogi and the height of the shinogi from the ha; from there it's basic trigonometry.

I think the 'drag' is more an effect of the broad edge angle causing wedging rather than directly caused by the shinogi itself. I imagine that you would experience similar amounts of 'drag' in all the lower cross-sections, if anything, the cross-section on the lower right (representative of a hira zukuri) would have the most as it is thickest at the mune and would be diverting the most force (of the three) to spreading the target.

I would be very interested in learning about the properties of the hyperbolic ha-niku and the parabolic hira-niku, but they would require equations just to define them properly.

Mark
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Mark H

#6 Ken-Hawaii

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Posted 16 January 2020 - 03:11 AM

Mark, you've again managed to ask quite a few questions in a single post. From my limited experience, the cross-section changes as a function of how many times a blade has been polished, as well as which of the nine possible ways to do the forging (kobuse & honsanmai were the most popular). The slimmer a blade's cross-section is, the easier it will cut, but also the more likely it is to bend or break, & the blade will need to be sharpened/polished more often, too. Niku of the boshi is important, but since the actual cutting is done on the monouchi, boshi niku plays less of a role than you might think. Overall blade niku is related to its cross-section.

 

A rather detailed paper was done by a friend of mine, Filomina Salvemini, & I've provided a link to the 1.6 MB file:

 

Attached File  Salvemini, Filomena - Structural Characterization of Ancient Japanese Swords.pdf   1.61MB   19 downloads


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#7 mas4t0

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Posted 16 January 2020 - 03:16 AM

Thank you Ken, sorry about the barrage of questions, your guidance is much appreciated.

I'll be looking over the paper with great interest.
Regards,
Mark H

#8 Ken-Hawaii

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Posted 16 January 2020 - 05:05 AM

Nothing wrong with asking questions, although I'll admit that yours are a lot more-specific than most. Here's some more reading material:

 

Attached File  Study_of_Japanese_sword_from_a_viewpoint_of_steel_strength.pdf   951.21KB   12 downloads

 

Attached File  Japanese Sword Materiel.pdf   753.11KB   11 downloads


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#9 Ken-Hawaii

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Posted 16 January 2020 - 05:07 AM

One more, written by an NMB member:

 

Attached File  On the origins of Nihonto.pdf   6.13MB   11 downloads


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#10 mas4t0

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Posted 16 January 2020 - 05:41 AM

Thank you Ken. Those are a great help.

I have one more question on this topic, and I'll try to keep it from being too open this time.

I can't tell from context if the cross-sections in this image are actual cross-sections or are imagistic representations.

jap_sword_complexity_time_large.jpg

Would you consider the cross-sections to be at all representative in terms of the geometry?
Regards,
Mark H

#11 Ken-Hawaii

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Posted 16 January 2020 - 06:11 AM

The geometry is pretty much as noted, Mark, but the actual images, as shown, are little more than illustrative.


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#12 Jacques D.

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Posted 16 January 2020 - 06:07 PM

That's a more complicated question than you might realize, Mark. In general, blade thicknesses in all dimensions increased in times of battle. Check out a Nanbukucho blade next to a Kamakura to see how different they look. You can blame the Mongols for scaring the crap out of the Shogunate, because the slim, elegant Japanese swords broke on Mongol armor!

 

The height/thickness of the shinogi, on the other hand, is much more idiosyncratic to particular schools. In general, older Yamato blades have a fairly-thin shinogi, for example.

 

I kindly disagree, Nambokucho swords, as they are very long have generally a thin kasane (just a matter of weight) Late Kamakura swords were more thick. Yamato blades show a high shinogi with a thin mune. After that, you can find a wide shinogi ji or a narrow one, that depends of the school.    

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#13 mas4t0

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Posted 17 January 2020 - 04:01 AM

Do any referance books give the dimensions of the thickness of the blade at the shinogi and the mune in addition to the other dimensions?
Regards,
Mark H

#14 Ken-Hawaii

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Posted 17 January 2020 - 06:28 AM

Not sure which reference books you are looking at, Mark. I went through a few of mine, but didn't see anything on kasane. Most books are pretty generic, & don't list much except hacho & sori, if that.


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#15 mas4t0

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Posted 17 January 2020 - 06:49 AM

Thank you again Ken, that's good to know.
Regards,
Mark H

#16 Jacques D.

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Posted 17 January 2020 - 10:52 AM

Do any referance books give the dimensions of the thickness of the blade at the shinogi and the mune in addition to the other dimensions?

 

Yes some books give it. 

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#17 mas4t0

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Posted 17 January 2020 - 05:09 PM

Yes some books give it.


Hi Jacques,

Could you please let me know which book that is?

Does it provide those measurements for most of the blades included or only a few?

Thank you.

Mark
Regards,
Mark H

#18 Jacques D.

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Posted 18 January 2020 - 12:57 AM

Iida Shinto Taikan, yes most of descriptions include kasane, same for the Shinshinto and Koto volumes. 


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#19 mas4t0

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Posted 18 January 2020 - 01:51 AM

Iida Shinto Taikan, yes most of descriptions include kasane, same for the Shinshinto and Koto volumes. 

 

Thank you Jacques.

I think I'll order one of the 3 volumes for the moment. Do you have a recommendation on which to start with?

Thank you.

Mark


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Mark H

#20 Jacques D.

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Posted 18 January 2020 - 09:25 PM

That depends of the era you are interested in, and it's your money (those books are not cheap) 

 

Author is Iimura not IIda as i said by mistake



#21 mas4t0

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Posted 19 January 2020 - 12:24 AM

Thank you Jacques.

In that case, I'll probably start with the Shinto set and go from there.

I'm planning to create 3d models of various blades in CAD software so that I can run some simulations on them and assess their handling dynamics and strength characteristics.

Is the text for the dimensions quite formulaic between swords?

I don't understand Japanese, but have several friends who do, so I would be able to get translations for any common terms.
Regards,
Mark H

#22 Austus

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Posted 19 January 2020 - 04:05 AM

That's where I was hoping you were going with this!   But if you eliminate niku, the study will be flawed in many ways.

 

Have you considered scanning blades from different eras, or schools, or certified cutting champions to find out what works best?   Geometry of design should transcend steel types or manufacturing techniques. What's the optimum edge angle in relation to the niku and placement of the shinogi, for example? Does it stay the same?  (Etc., etc...)  You could compare any element in the equation against your own models or others. 

 

Sword Dynamics could be its own Science!   Just sayin'.


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#23 mas4t0

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Posted 19 January 2020 - 04:22 AM

Hi Austus,

I will be applying niku to the models, but I need mathematically actuate basic geometry for the foundation.

As I won't be able to get an accurate understanding of the nature of the niku on each blade, I'll be applying the same level of niku to each (the actual thickness will be proportional to the edge angle described above). So I won't be eliminating it from the tests, but more eliminating it as a variable, if you see what I mean.

I could do a purely theoretical analysis, and determine the optimal angles and geometry for a given metallurgy and heat treatment when subjected to particular usage cases, but I'm more interested for now in a more empirical analysis of historical blades.

If it was purely theoretical, the optimisations would be responses to the criteria I (somewhat arbitrarily) set rather than anything particularly representative of real world usage.

All things being equal, a hira zukuri will cut the best on a soft target, but it is also going to perform the worst in the event of an off angle cut, be the weakest laterally and the most prone to chipping.

There's also the issue of how to weigh the variables, many of which are mutually exclusive and therefore a comprise.

The analysis should show it up, but I think that the different blade geometries are more different than they at first seem. I think that the analysis will clarify my meaning to a greater extent. That's just a long way to express, that I think there is a lot more variation than meets the eye.

I'm glad to see we're on the same page, I think we may have had crossed wires earlier.

Thank you for your input, and if you have any other thoughts, please let me know.

Regarding scanning; I don't have any expertise with this. I don't know if it would be possible to get an accurate scan of a curved and polished surface, but it's certainly beyond my capabilities.


Mark
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Mark H




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