traditional katana physics

[Bors]

If you were planing on facing armored opponents I'd suggest something other than a sword. Axes, maces, and polearms are kind of the only route to take short of wrestling your adversary to the ground via half-swording and then stabbing them in the neck once they're on the ground.

The sword is generally not the primary weapon on the field. Maces and axes are never dropped the hafts never break, spears never splinter and one never has to rely on his sword...

 

[FortyTwoBlades]

If I wasn't equally armored and my axe/mace etc self-destructed on me I'd be running away! Distance is the best defense! And I did mention half-swording. That and batting them repeatedly in the head as much as possible would work ok. It might not hurt them much but it sure is disorienting!

 

[Bors]

If I wasn't equally armored and my axe/mace etc self-destructed on me I'd be running away! Distance is the best defense! And I did mention half-swording. That and batting them repeatedly in the head as much as possible would work ok. It might not hurt them much but it sure is disorienting!

Interesting approach....

 

[Bors]

When a sword is picked up the first thing that is noticed is how it “feels”. Feeling is based on three things, the handle , overall weight and blade presence (placement of the COG). The overall weight of the sword and the COG gives a good clue to how the sword will handle. This is a personal preference so the numbers either work or they don’t based on what the user is looking for. If the handle is poorly shaped to large Etc, then it really doesn’t matter how good the numbers are the sword just won’t feel right. You still won’t know how the reacts. A solid whack to the pommel will give you a clue as to how well it’s dampened.

If a suitable sword is not found then an order is placed with the smith. The overall weight must be X and the COG to be placed at X” before the guard and the handle shape is to be X. Once again it boils down to personal preference and usage. What do "you" prefer and what will it be used for.

 

[the possum]

Admittedly my first reaction is to not bother with a reply. But, hey, maybe somebody else is wondering about this too, and it would be a disservice to them to allow misconceptions to keep being perpetuated.

The idea that the COM is what controls handling or impact behavior by itself is a deep rooted misconception.

When a sword is picked up the first thing that is noticed is how it “feels”. Feeling is based on three things, the handle, overall weight and blade presence (placement of the COG). The overall weight of the sword and the COG gives a good clue to how the sword will handle.

When you just pick up a sword and hold it out, yes, the COM/COG is what you're feeling torque your wrist. But this is not what's important when you throw a zwerchhau to the opponent's right side and then whip another around to his left when he tries to displace. That involves spinning the sword around in a circular arc with mainly wrist power, and is controlled mainly by the moments of inertia.

If you don't want to take my word for it, then here's what Tinker Pearce has to say:

"So- take two swords with the same length of blade and the same weight and Center of Gravity (COG). For argument let’s say that both swords have 32" blades and balance four inches from the cross. One sword is made from 3/16 inch stock and has little profile and no distal taper with a heavy pommel to draw the COG back to four inches. The classic 'sharpened bar' type of sword. The other sword is 3/8" thick at the base but has a good amount of profile and distal taper. This sword doesn't need a heavy pommel to draw the COG back because of the distal taper, so the swords are of equal weight. Despite both swords weighing the same and having the same center of gravity the second sword will feel lively in the hand, and the first sword will feel like a club."

So, if you only specify weight, length, and the center of mass, you may get a great handling sword, or you may end up with a club. But perhaps at least it will be a club with the perfect handle shape...

 

[Bors]

The idea that the COM is what controls handling or impact behavior by itself is a deep rooted misconception.

Yes it does control how it handles and it's not a misconception.....you just said it below but I don't think you realize it....

When you just pick up a sword and hold it out, yes, the COM/COG is what you're feeling torque your wrist. But this is not what's important when you throw a zwerchhau to the opponent's right side and then whip another around to his left when he tries to displace. That involves spinning the sword around in a circular arc with mainly wrist power, and is controlled mainly by the moments of inertia.

Your in the ball park....... Take a close look at what is really happening......

 

[the possum]

Yes, I realize that the COM is part of the equation for the moment of inertia, and thus cannot be entirely discounted or separated from the rest. And I know it's mainly what you feel statically, and that it affects linear motion. (Which is why I mentioned a move involving mostly rotational motion as an example.)

I am just trying to get the point across that there is much more to sword behavior than the location of the COM. And that simply saying "Placing the COG closer to the point increases blade presence (the blade feels heavy)" is an incorrect statement, if we want to talk about anything other than holding the sword still in your hand to admire it.

Cheers.

 

[wnease]

With sportbikes we often talk about mass centralization for more agility. I suppose the most agile sword for a given mass is a sphere of high density, likewise for the bike, but this doesn't help much! Is the center of mass the balance point? How does this differ from the center of gravity? On a katana, how far can the balance point go before it is unuseable as a sword and is more like an unusually shaped axe? More importantly, how far forward is it on swords you have handled? How is (polar or otherwise) moment of inertia quantified?

 

[the possum]

Sorry I haven't had time to reply; even now I'm pressed for time. Here's a couple things to get you started.

The moments of inertia are directly linked to the pivot points, which are described in this article on the ARMA site: Sword Impacts & Motions

Vincent LeChevalier is another guy really interested in this stuff, and he shared some of the math formulas with me to find the moment of inertia based on the pivot points; I can provide them if you like.

He has also taken a different approach to describing mass distribution, that ties right in with something you said. Actually, I'm using the terms center of mass, balance point, and center of gravity interchangeably to describe the balance point- where the sword will balance if you let it rest horizontally on one finger. But Vincent seems to be having some luck describing a sword as nothing more than a stick and a point mass. See here: Breakthrough about sword balance

Unfortunately I don't have my notes on the measurements I took from my great uncle's swords, and the COM is not something usually recorded in traditional measurements. But again, don't place too much emphasis on the COM. It may be the same as a good antique, yet handle and cut totally differently.

 

[Bors]

With sportbikes we often talk about mass centralization for more agility. I suppose the most agile sword for a given mass is a sphere of high density, likewise for the bike, but this doesn't help much Is the center of mass the balance point? How does this differ from the center of gravity? On a katana, how far can the balance point go before it is unuseable as a sword and is more like an unusually shaped axe? More importantly, how far forward is it on swords you have handled? How is (polar or otherwise) moment of inertia quantified?

The COG or COM with respect to swords are used interchangeably even though technically they are different. Since both are used to generally describe the same point that is the point of neutrality or equilibrium it’s dealers choice as to which one you want to use. The COM is the exact point where the sword balances or is at rest but it is the point where it “wants” to rotate and will do so with the least amount of resistance one example being, I had the opportunity to visit a decommissioned OSCAR 1 underground nuclear missile command center the main door or blast door weighs 10 tons and can be pushed open with two fingers. Again rotation at the COM requires the least amount of effort. Some techniques require a rotation point farther away from the COM requiring more effort to execute.

The Balance point of swords very massively depending upon intended or designed use, for example a particular sword cain I had balanced well behind the separation point (where the handle ends) making the point extremely fast. It had no edge only a point so speed and agility were it’s design. Now on the apposite end of the spectrum of swords you have the Falchion. Falchions very in design but generally are much wider towards the point. This moves the COM much further forward then a normally proportioned sword of the same size. But the whole reason for this is to increase how hard it hits.

The cover of a book will provide a glimpse into the book but won’t tell you the whole story likewise the position of the Com will not tell you how well the sword cuts but it will show you where the sword wants to be rotated and will give you an idea of how the sword will feel. Some swords have reduced mass in the forward portion of the blade to quicken it up. I handled a sword and the COM was about where you would expect it however the blade was very light to the feel. This is all well and good for a dueling sword however, the trade off from the reduced mass is cutting performance.

There are plenty of web sites and books out there that will provide you and you calculator with a good work out. It’s very easy to over analyze and get lost in all the math. Just a word of caution....

Of the katanas I have handled the Com was ~3" - 5" before the guard however like I said it will very greatly. Just an observation which may or may not be correct but I tend to think that Japanese swords are balanced unmounted. I say this because Pommels and guards on European swords are rarely changed so are considered part of the sword and as such are factored in as part of the balancing process whereas with Japanese swords the handles and fittings very radically in design are not considered part of the sword.

 

[the possum]

I am still learning about this stuff. Heck, I didn't end up getting my practice sword quite the way I wanted it, so I don't want to come across as being preachy here. But, in the spirit of learning, I'll say this statement is once again not quite correct.

Some swords have reduced mass in the forward portion of the blade to quicken it up. I handled a sword and the COM was about where you would expect it however the blade was very light to the feel. This is all well and good for a dueling sword however, the trade off from the reduced mass is cutting performance.

Here is an example from personal experience that refutes the above statement- I did a bunch of work on my Khukri to make it handle and cut better. I removed a bunch of mass from the blade, and then added a pommel which brought back the balance point considerably. Yet I got more cutting power at the tip after my modifications. I went into details here. So in this case, there was really no trade off involved; I enhanced both handling dynamics and cutting ability at the same time by improving the balance. This is predicted perfectly by paying attention to the pivot points, and goes directly against much of what you're saying about the COM.

The COM is the exact point where the sword balances or is at rest but it is the point where it “wants” to rotate and will do so with the least amount of resistance...

I don't think I have time to address this right now... I may just be misunderstanding what you're getting at, anyway. Would you care to elaborate how rotating a sword around its COM is used in swordplay?

 

[wnease]

awesome info on your kukri mod!

 

[Luis Felipe Silva]

hi, i would like to know if there are any katanas from nagasone kotetsu (altentic ones) for sale and if anyone can tell me where can i find them, plese e-mail me :lfelipe.sampaio@hotmail.com



luis felipe sampaio

 

[Luis Felipe Silva]

You could fill up volumes with each point in your question LOL.


Keeping in mind you’re a sword maker so as not to ramble on to much since your interested in mainly cutting performance I would start by researching a 17th century smith by the name of Nagasone Kotetsu. His swords seem to be held in high regard for cutting ability.
This is one of his swords. The Tameshigiri inscription says it cut through three bodies. Tameshigiri at that time was performed on live prisoners or criminals.

The handle and furniture on the swords were subject to change. A change in rank might require a different handle wrap as well as different fittings. The sword might have two handles one for EDC and one for court. The material used for the furniture varied greatly from horn to silver, gold and iron, in addition simple or complex designs also effected the weight of the furniture. The balance of the sword can be affected buy theses changes. Presumably an attempt would be made to match the handles so as not to effect the balance to greatly but then again maybe not.

Very complex swords...

where can i buy one of those katanas(nagasone kotetsu), can you help me? my name is luis felipe; may e-mail address:lfelipe.sampaio@hotmail.com

 

[Luis Felipe Silva]

You could fill up volumes with each point in your question LOL.


Keeping in mind you’re a sword maker so as not to ramble on to much since your interested in mainly cutting performance I would start by researching a 17th century smith by the name of Nagasone Kotetsu. His swords seem to be held in high regard for cutting ability.
This is one of his swords. The Tameshigiri inscription says it cut through three bodies. Tameshigiri at that time was performed on live prisoners or criminals.

The handle and furniture on the swords were subject to change. A change in rank might require a different handle wrap as well as different fittings. The sword might have two handles one for EDC and one for court. The material used for the furniture varied greatly from horn to silver, gold and iron, in addition simple or complex designs also effected the weight of the furniture. The balance of the sword can be affected buy theses changes. Presumably an attempt would be made to match the handles so as not to effect the balance to greatly but then again maybe not.

Very complex swords...

where can i buy one of those katanas(nagasone kotetsu) the altentic ones? can you help me? my e-mail is:lfelipe.sampaio@hotmail.com

 

[Lee Bray]

Kotetsu blades are available but you will need to contact the top private collectors or go to the Dai Token Ichi event in Tokyo every October which is the largest yearly dealer show in Japan.
There are sometimes one or two available.
Be prepared to spend between US$50,000 - $150,000, though, as they don't come cheap.

Edit - Here's one that maybe available.
http://www.nihonto.com.au/html/kotetsu_.html

 

[Lycosa]

Thanks for a very interesting, Gentlemen!
Hi William.

 

[Luis Felipe Silva]

Kotetsu blades are available but you will need to contact the top private collectors or go to the Dai Token Ichi event in Tokyo every October which is the largest yearly dealer show in Japan.
There are sometimes one or two available.
Be prepared to spend between US$50,000 - $150,000, though, as they don't come cheap.

Edit - Here's one that maybe available.
http://www.nihonto.com.au/html/kotetsu_.html

i did´t find the nagasone blade, i would like to know if anyone of you can help find even an imitation of it or replica(with quality and cutting capacity for tameshigiri)?

 

[Luis Felipe Silva]

i didn´t find the nagasone kotetsu blade, but i would like to know if anyone can help me find an imitation or replica of it(with good quality and cutting capacity for tameshigiri)? please i would very much apriciate the help.

 

[Luis Felipe Silva]

i didn´t find the nagasone kotetsu blade, but if anyone knows were can i find even an imitation or replica of it (with quality and cutting capacity for tameshigiri) i would very much apriciate.