Question regarding why a Katana can cut the way it does...

[Kaoru]

Hi Minna-san!

I am wondering if anyone can help me answer the following question I found on the Samurai Forum.

"Please provide a brief explanation as to why with such a small force, the japanese sword can deliver such a powerful cut and effective damage to a target if done properly"

Here is the link to see what others have already said. Only 3 so far have given an explanation, but, none has really answered the question as to WHY it can cut powerfully with just a little bit of force, if the cut is done properly. I replied and said I'd go find out why, if I could. Well, it interests me too... I don't practice an art using a blade, so that's why I am looking it up. I searched all over the web, and then this site, but I didn't know how to define my search, so now I have to ask.

So, all I know, is that it must have something to do with the curve of the blade, and whether hasuji is done right. But, that's all I know, so I can't put that in a reply, because I have no idea how to explain those things right.

Here is the link:

http://www2.g-com.ne.jp/~japan/cgi-b...t=ST;f=5;t=160

Can anyone please tell me what I ought to post for him as an answer? I need a concrete reason with maybe some scientific reasons, if anyone knows it. Thank you all so much for helping me out! Hopefully I'll learn something as a result too!

Thanks again!

[Ralutin]

Hi Carolyn,

I just posted in my two cents on the other board. Perhaps some of the batto-ryu folks in this universe (forum) have some better insights on cutting as they do alot of it with relative ease.

Regards,

[DCPan]

From the iaido-l archives

http://listserv.uoguelph.ca/cgi-bin/...R29153&m=11788

- - -
Date: Tue, 9 Feb 1999 13:23:00 -0500
Reply-To: Japanese Sword Art Mailing List <IAIDO-L@LISTSERV.UOGUELPH.CA>
Sender: Japanese Sword Art Mailing List <IAIDO-L@LISTSERV.UOGUELPH.CA>
From: Robert Stroud <RStroud@COMPUSERVE.COM>
Subject: Shape of Nihontoh
Content-Type: text/plain; charset=ISO-8859-1

As I read the posts about blade shape, and curvature
and swing I get real interested. In the past I have taken
advantage of the work by Dr. Sam Saunders, Dept of
Mathematic Washington State University. Dr. Saunders
has put together an, as of yet un published paper, regarding
the mathematics pertaining to the curvature of the Nihontoh,
Japanese blade. I have applied the math of the Japanese
blade to my designs of manufacturing equipment.

Basically, the equation of curvature, is (from memory, which
after many many many men hits, isn't what it should be)...

R=beta*e^^(alpha*theta)

R= radius of curvature
beta=constant
e= natural log
alpha= constant
theta= angle along the curve

What Dr. Saunders found was that the Japanese blade has
a constant curvature following the above equation. The shape
of the equation if you plot it out is the familiar outward spiral of
a Nautilus Shell. The two interesting points to think about are
that one, with the above construction the 'angle of attack' remains
constant thru out the blade rotation. The angle of attack can
be thought of at the angle between the surface being cut, and
a tanget line on the blade's curvature. If the blade has a constant
angle of attack, it will cut consistantly thru out the swing. All
a smith has to do is decide the optimum angle of attack, and
you determine how the actual cutting will happen.

The second point, is that the blade was developed empirically.
There were not calculations to determine how to do this, but rather
the Japanese smiths of old, zero'd in on this thru trial and error.
The same curvature can be found, in reverse, on blades found
in other parts of the world.

When you swing the shinai or the shinken (real sword) you swing
the same, but with a shinken it will cut when it impacts the target.
This is why kendo sensei tell you not to force the swing or hit
too hard, they tell you the blade will cut by itself with a correct swing
Well you you have the math to show them just how true this is.

Remember, the shinai will swing just like a shinken, but once it
impacts the target, the only difference is that no cutting occurs. In
fact if you look at still photos, taken just at the impact, the shinai
will assume the shape of the shinken. Food for thought isn't it.

Best regards and happy swings,
Robert Stroud
Obukan Kendo Club
Portland, Oregon, USA

[Tea Guy]

If you have a decent non-serrated cooking knife at home it will help with my explanation.
First off, as others have said, the curvature of the blade is extremely important. It allows for the blade to constantly be in contact with the item being cut. This is very important. If the blade were straight it would not have the same natural flowing cut.

Now, for the second part of my explanation to help you understand by experience. As was also stated, proper technique is a must. Without proper technique the blade doesn't cut smoothly and can be potentially dangerous. A katana uses a "slicing" type of action.
You ready for the experience part? Take a sharp non-serrated cooking knife and a piece of meat.
Set the piece of meat on the cutting board.
Put the edge of the knife on the piece of the meat and push straight down, keeping your fingers out of the way. Do you see how difficult it can be cutting this way? Do you see how much pressure you use? Once again, do be careful in demonstrating such.
Now, to illustrate the proper cutting motion, take that same piece of meat and the same cooking knife. Place the edge of the knife on the piece of meat and gently pull the knife backwards without putting great force on the blade. Don't use a back and forth sawing motion. Just a smooth drawing cut. The weight of the blade should be doing most of the work. Do you see how the meat is cut easily without much force? This is the basic idea of the cutting motion of a katana.

The edge of the blade stays in contact with the item being cut largely due to the curvature of the blade. This makes it much easier to cut things if proper technique is used. That means not using it with a straight swing like a baseball bat or a club, but rather....well....like a katana.
I hope I've helped.
In addition to that, if you did the example you just learned the most basic and important of knife techniques in the kitchen and with practice will have no trouble carving meats and will simply scoff at the idea of "electric carving knives".

C.Sieg

[Tea Guy]

Oh hey! I just checked that site and someone gave an example similar to mine! Ha!
Well....I think that using a piece of meat is a better example than a tomato anyway.

C.Sieg

[Kaoru]

Originally posted by Tea Guy
Oh hey! I just checked that site and someone gave an example similar to mine! Ha!
Well....I think that using a piece of meat is a better example than a tomato anyway.

C.Sieg

Hi!

But yours was easier to understand... I'm a Kendoka, so I only use bokken and shinai... I've never held a sword.

Hey guys, if you all don't mind, I think I am going to turn this thread into a link on the other forum for the person who asked. If I try to copy and paste all these explanations, my post will be a mile long there.

Wow, I really appreciate everybody's help. Really. I'm going to carefully try the experience part of your post, Tea Guy-san. Then, I will really see what you mean.

Oh, and Pan-san, thanks for the scientific explanation you found, too. I am sure Kasuki-san, who posted the question, will be happy to see it, as well as all the other helpful posts. If anyone else has any other explanation, go ahead and post it...

Domo arigato gozaimasu minna-san!

[Dan Harden]

We should all recognize that many men have postulated and calculated any number of "theories" about things they have a passion for. Superior? Perfect? These are words I would not use freely when discussing various cultures weaponry.
Discussions of angle-of-rotation and maintaining an angle-of-rotation through a cut are nonsense when the angle of impact is a moving object and the rate of deflection inherent in _that_ reality are not accounted for in the lab. As well, we have the various absorptive rates of various "supposed" targets. Because of these things your hands will not maintain anything even remotely approaching a measurable "angle-constant" with the various things a blade can encounter. You have a positional relationship to the target that makes a mockery of any "model" and blows theories right out the window.

I could argue that the Japanese blade has demonstrated that straight impact force is superior to cutting since a straight blade will more often present a slicing motion to a target..........what?"
An example of this is as follows:
Take your "piece of meat" and place it on a horizontal rod in the air a little below chest level. Rotate the Katana in the hand and you will have an almost straight downward impact force. Now use a straight blade. The straight blade will make a slicing angle on impact due to your body’s position to the target. On impact its straight edge created an angle to the target-the position of the hands causing it to slice through. Some arts cut out, down and back in, some cut out with a lever motion. How do the resultant motions affect impact-to-cutting power?

The sharpness and polish is an exactly wrong for cutting as well. Almost any knife maker with experience will tell you that a polished edge will work for impact shear, but a 400 grit edge has more "teeth" for cutting anything. Another argument for a katana's impact force over slicing model.

But now try any of this with real people moving! It’s all a bunch of hoo-ha.

The curve of a Katana also has much to offer that has "nothing" to do with cutting-well not directly- although it ends there.
At any rate cutting soft targets just does not require that much effort.

I personally enjoy bringing a Kukri to cutting sessions and matching or outdoing cuts made with a 30" Katana with a two hand swing with a single hand cut from a blade half that size. This is particularly fun with Samurai Japanophiles.

Ever cut with a Yatagan? Like the Kukri- the blade is curved in the other direction! It is equally revealing to see what a _straight_ blade will do-heck even a sharpened bar of flat stock _unheatreated_ will cut well. What about a thousand years of other cultures using straight blades?
We all love the Japanese sword-but more nonsense has been written about its supposed attributes than any other blade in history. I am still thinking about showing up at one of these American Japanese-grass-cutting shabangs with a used lawn mower blade with the hole still in the middle mounted in full koshirei (maybe with a grass stalk engraved tsuba) and cutting with it.

Cheers
Dan

[charlesl]

Well, probably a lot of you have seen this, but for those who haven't:

http://www.thehaca.com/Videos/quicktime/ohdeer.mov

Probably not applicable to anything, but makes for interesting viewing.

-Charles Lockhart

ps. That's a link to a large file (5mb, not large for me, but for some), may be easier to right click and select "save target as" and actually download it.

[Chidokan]

Originally posted by Dan Harden
But now try any of this with real people moving!

Any volunteers? (bearing in mind those two nutters in germany, one of whom volunteered to be killed and eaten by the other)

Seriously though Dan, what do you reckon is the best way of sharpening a sword?

[pgsmith]

Carolyn wrote ...

"Please provide a brief explanation as to why with such a small force, the japanese sword can deliver such a powerful cut and effective damage to a target if done properly"

I believe that what Dan was trying to say with his curmudgeonly rant (that's OK Dan, we need curmudgeons!) is that you really need to remove "japanese" from your question. Basically all swords with an edge will deliver alot of "effective damage" if used properly. After all, that's why they were created. They are large person cutting knives. (OK, so rapiers are person pokers not cutters.) The point is that they are meant to create horrific wounds whether they are curved as the Japanese blades, or straight as many European swords.

Most of us that practice diligently to try and use these things properly never bother to worry about why something happens. We are just worried about what we are supposed to make happen. If I strike but don't cut, I don't bother to do the math and try to figure out which angle was wrong or why I didn't cut. I try and figure out what I did wrong since I know that it is supposed to work.

I think you would do your friend on that other forum much more of a favor if you told him not to worry about trivial questions such as he asked, but to find an instructor and work on it personally.

Just my two cents!

Cheers,

[gmlc123]

Apart from the sori of the blade which helps, the other main reason traditional Japanese swords cut so well is because of the profile shape and cutting angle of the Ha.

The cutting edge on traditional swords is a full convex (AKA moran edge), and this creates far less friction when cutting vs a three-angle simulated convex that are used on most modern taiwanese production blades or a straight angle edge.

[Cady Goldfield]

I'm surprised that no one has addressed the role of the person doing the cutting. With proper technique, angle and acceleration, a skilled swordsman can cut with any blade (Dan touched on that somewhat when he mentioned the lawnmower blade).

A nice honed edge, of course, helps make a cut cleaner and tighter, but such an edge can be made on anything from a Ginzu kitchen knife to a piece of sheet metal.

It's not the blade, it's what's wielding the blade. Technique, technique, technique.
A skilled cutter can even "cut" barehanded -- shuto. Geez, back in my karate days, I could slice through a watermelon with the edge of my hand. What's all the fuss about with Japanese swords??

[gmlc123]

Isn't that fact taken for granted... and I thought the topic was about the physical/scientific characterisitics of a Japanese Katana, not the person using it, that allows the "sword" to produce a very efficient cut in comparison to other blades/swords?

Individual blades characterisitics and geometry are what make some swords better cutters than others in the hands of the same user, even if it's a Soke using them.

Originally posted by Cady Goldfield
I'm surprised that no one has addressed the role of the person doing the cutting.

[Kaoru]

Originally posted by pgsmith

I believe that what Dan was trying to say with his curmudgeonly rant (that's OK Dan, we need curmudgeons!) is that you really need to remove "japanese" from your question. Basically all swords with an edge will deliver alot of "effective damage" if used properly. After all, that's why they were created. They are large person cutting knives. (OK, so rapiers are person pokers not cutters.) The point is that they are meant to create horrific wounds whether they are curved as the Japanese blades, or straight as many European swords.

Most of us that practice diligently to try and use these things properly never bother to worry about why something happens. We are just worried about what we are supposed to make happen. If I strike but don't cut, I don't bother to do the math and try to figure out which angle was wrong or why I didn't cut. I try and figure out what I did wrong since I know that it is supposed to work.

I think you would do your friend on that other forum much more of a favor if you told him not to worry about trivial questions such as he asked, but to find an instructor and work on it personally.

Just my two cents!

Cheers, [/B]

Hi Smith-san,

Oh, Dan-san's post was fine. I just didn't understand what he was talking about. I got lost when he started talking about different kinds of blade types and the other words he used that I didn't know.
I was going to come back to ask what he meant, but you beat me to it. Thanks for explaining what he meant!

Oh, my friend does have a sensei. He just wanted to know about the scientific part of cutting, besides the other reasons why the katana can cut the way it does.

I guess that the more experience one has training, the more a person can understand why, right? That's in reply to what you said here:

Most of us that practice diligently to try and use these things properly never bother to worry about why something happens. We are just worried about what we are supposed to make happen. If I strike but don't cut, I don't bother to do the math and try to figure out which angle was wrong or why I didn't cut. I try and figure out what I did wrong since I know that it is supposed to work.

But, it is nice to learn the scientific reason, too. But, I think I understand what you are saying. So, you mean that how you hold the sword and your hands and body has a lot to do with whether or not the sword will cut effortlessly too, right?

Oh, what is "sori" please?

Anyway, I'll point him to this thread again to see this.

[Tea Guy]

"Sori" is the term used for the curvature of the blade. I probably should have mentioned that earlier in one of my earlier posts. There are different types of sori which differ by the depth of the curve and where the blade curves the most. For example, Toriizori refers to the center of the curvature of the blade being at about the middle of the blade and even, while Koshizori has the deepest part of the curvature about the lower 1/3 of the the blade.

Also note that this sori gives a smoother feel to the cut than a straight blade (if used properly).


I can certainly understand a person's curiosity though. I don't think that you only need to go to the dojo to understand. There are probably many people who practice sword arts, but have never actually cut anything. This can be a problem when they start. One should have a basic knowledge of HOW blades cut. That was the reason of my earlier post. I have met and seen numerous people who don't know the proper cutting technique of any type of blade. That covers the kitchen as well. I have seen people using a sawing motion with a great deal of pressure when trying to cut a roast or a turkey. However, if one is fully aware of how to use a blade they can carve something with 1 or 2 gentle, flowing movements of the blade and have a very smooth cut that is far more accurate. This particular movement should become natural for the practitioner.
Remember, the blade cuts...not you (how many times have you heard that before?). You merely guide the blade. Using a straight swing can get the blade lodged in your target and possibly damage the blade. On the other hand, if you remember the way a blade cuts, you will remember that the blade will cut something quite cleanly when it slides along the cut as it is being formed.
Did you try the "experience" thing I suggested?

C.Sieg