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Jesse Eaton





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PostPosted: Thu 20 May, 2010 9:10 pm    Post subject:         Reply with quote

A couple of points here...

1. Center of mass does not mean the same thing as point of balance. Point of balance means the spot on a blade where it will balance. Center of mass is exactly that- the center of the mass of the weapon. A double edge sword with a simple hilt will almost assuredly have the same CoM as its PoB but a curved blade certainly will not.

2. Michael cannot be wrong about what he feels because he would have to pick out the feeling he is denying that he is having in order to deny that he is in fact having it. Thus the denial of the claim affirms the claim making it undeniable Happy

Sorry about the second point, I have to make the most of my degree in Philosophy
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Timo Nieminen




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PostPosted: Thu 20 May, 2010 9:41 pm    Post subject:         Reply with quote

Jesse Eaton wrote:

1. Center of mass does not mean the same thing as point of balance. Point of balance means the spot on a blade where it will balance. Center of mass is exactly that- the center of the mass of the weapon. A double edge sword with a simple hilt will almost assuredly have the same CoM as its PoB but a curved blade certainly will not.


For example, for a highly curved blade, the CoM can lie off the sword. The point of balance, as defined above, always lies on the sword. In such a case, the PoB will usually be the point on the sword closest to the CoM (some variation is possible with a bizarre sword, but often in this case the PoB is not a very useful concept).

For a curved sword like this, if you want to describe the handling with a few numbers, the CoM is better since how far it is away from the blade affects the handling.

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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Michael Edelson




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PostPosted: Thu 20 May, 2010 9:55 pm    Post subject:         Reply with quote

Timo Nieminen wrote:

Try it sensibly, rather than with a ridiculous choice of weight.

Choose a bar and pommel so that the total lengths are as above, COG 4", weight 3lbs. This is possible; you can really do this and try it for yourself. Will it handle like a well-balanced sword?

You can be even more extreme. Get the lightest bar you can, and add weight to the tip and pommel until it's the weight of a sword, with the CoM where you want it. Will it handle like like a well-balanced sword?


But those things wouldn't be swords. I am not after some universal method of measuring that would result in predictable handling for any object that can be wielded like a sword. Given a specific type of sword, made like a sword, and made well, then all I need is COG and weight. I never claimed more than this.

If you want to use measurements that can tell what any random shaped object is going to feel like, then obviously you need a lot more than that. I, on the other hand, do not.

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Thom R.




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PostPosted: Thu 20 May, 2010 10:25 pm    Post subject:         Reply with quote

Michael Edelson wrote:

Given a specific type of sword, made like a sword, and made well, then all I need is COG and weight. I never claimed more than this.


I understand you. I liken it to my friend who is in law enforcement who can accurately (within 2,3 mph) tell how fast people are driving by just through observational skill. that is because he has spent 1000s of hours with a radar gun on the side of the road in his career. and now he doesn't really need the radar to gauge the speed of a passing vehicle.

however for some of us, myself included, the measurements of mass distribution beyond just POB are still important. especially for those of us engaged in the making of things "well". and yes, i am the final arbiter of my own reality too. Razz tr
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Timo Nieminen




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PostPosted: Thu 20 May, 2010 11:28 pm    Post subject:         Reply with quote

Michael Edelson wrote:
Timo Nieminen wrote:

Try it sensibly, rather than with a ridiculous choice of weight.

Choose a bar and pommel so that the total lengths are as above, COG 4", weight 3lbs. This is possible; you can really do this and try it for yourself. Will it handle like a well-balanced sword?

You can be even more extreme. Get the lightest bar you can, and add weight to the tip and pommel until it's the weight of a sword, with the CoM where you want it. Will it handle like like a well-balanced sword?


But those things wouldn't be swords. I am not after some universal method of measuring that would result in predictable handling for any object that can be wielded like a sword. Given a specific type of sword, made like a sword, and made well, then all I need is COG and weight. I never claimed more than this.


I said as much myself; I quite agree. Assuming that you are familiar with the handling of the type of sword in question.

The mass distribution affects the handling, and the mass distribution is sufficiently described by mass, CoM, and MoI. I never claimed more than this. You commented on this claim, and I elaborated on why mass distribution is important.

CoM, mass, and MoI [1] can tell you how a completely unfamiliar type of sword will handle, or how a badly made sword wil handle. It can even be useful for telling you just how well- or badly-balanced a particular sword might be, which might be of use for some people, even if you have no need of it. Just add a third number to the original two, either MoI, or CoP (rotational dynamics version), and you have a lot more information.

[1] To make it really general, you need the moment of inertia tensor, not just a single number for the moment of inertia. But this will be enough for any rigid object.

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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Vincent Le Chevalier




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PostPosted: Fri 21 May, 2010 1:50 am    Post subject:         Reply with quote

As some of you know I've been thinking about all this far too much Happy

I think Michael's observation is actually correct: for a given type of correctly made swords, you don't need more than CoG, total mass, blade length, hilt length to draw conclusions on handling. That's because the position of the pivot point seems to be set by type, hilt length and blade length on correctly made swords, as a first approximation.

The pivot point, or more accurately CoP or CoO (center of oscillation), associated to the junction cross-handle tells how long the sword feels. The longer it is, the more stable it feels. Having an 'unstable' sword with a close CoO makes plenty of sense for a cutting weapon, because it swings faster into cutting motions. Having a stable sword is more important for thrusts.

It's not that this measurement is useless in my opinion, it's just that if you select well-made weapons within a sufficiently narrow type, it cannot really be surprising. It gives some more information but it's second order.

On the other hand, I'm personally also interested in being able to compare across types. For example, the label rapier is attached to so many things that the complete dynamic measurement is necessary to make distinctions and more detailed classifications within these types in my opinion. Also, the design of training weapons (that have to make some compromises not representative of real swords) benefits from the full understanding I believe. And theoretically it is interesting Happy

I'm currently writing an article specifically about how to measure a sword for its handling. I still need to shoot some pictures illustrating the process, as Michael says finding the CoO is not really straightforward and the measurement is hard to accomplish unless someone shows you how to do. Now that I have successfully defended my PhD (unrelated to swords Wink ) I hope I'll be able to progress faster on that...

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PostPosted: Fri 21 May, 2010 2:10 am    Post subject:         Reply with quote

Vincent Le Chevalier wrote:
I think Michael's observation is actually correct: for a given type of correctly made swords, you don't need more than CoG, total mass, blade length, hilt length to draw conclusions on handling. That's because the position of the pivot point seems to be set by type, hilt length and blade length on correctly made swords, as a first approximation.


I sort of disagree with this in that swords are built for different purposes and so often have different design characteristics that create varying dynamic properties. To say that all "correctly made swords" are made with the same basic properties is factually incorrect.

Now it is true that many replica swords happen to be made with the same formula. This is because 1) the average maker doesn't take the time to document a variety of swords 2) the customer base for swords has a notion that all swords are supposed to feel a certain way (the "correct" way) and 3) swords made outside of this common formula are often specialized and so aren't appealing to a wide audience.

The two examples I brought up earlier in this topic are both examples of what I mean: the Albion Svante and the A&A German Bastard Sword. Neither of these swords follow the "common formula" and yet are certainly "correctly made".

By the way, I'd like to add that my comments are coming from a guy who doesn't really care about the numbers and doesn't feel the slightest need to quantify dynamic properties, etc. Ironic, huh? For me, sword design is fascinating because of the complexity and variety of designs. I enjoy being surprised by a sword once it is in hand. It's happened many, many dozens of times and each time I get a kick out of it.

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Vincent Le Chevalier




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PostPosted: Fri 21 May, 2010 2:21 am    Post subject:         Reply with quote

Nathan Robinson wrote:
Vincent Le Chevalier wrote:
I think Michael's observation is actually correct: for a given type of correctly made swords, you don't need more than CoG, total mass, blade length, hilt length to draw conclusions on handling. That's because the position of the pivot point seems to be set by type, hilt length and blade length on correctly made swords, as a first approximation.

I sort of disagree with this in that swords are built for different purposes and so often have different design characteristics that create varying dynamic properties. To say that all "correctly made swords" are made with the same basic properties is factually incorrect.

Well as I said, that's a first approximation. Of course there are models pushing the envelope and going away from the average, and personally I wouldn't neglect pivot point, but I sort of get what Michael is saying. Also, we don't know exactly how many types of swords Michael distinguishes functionally. Maybe the Svante and GBS are in special categories in Michael's mind?

Regards,

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C Bosh




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PostPosted: Fri 21 May, 2010 2:23 am    Post subject:         Reply with quote

The internet is a wonderful place and most people now buy there swords that way., but there is no better judge than hands on feel. facts and figure can give you some ( in some cases, most ) of the story but not all, it has to be hands on. This is hard when you are mile away from the seller, but that is what this forum is about- to pass on information we all have gained
I belive facts and figures can never tell the hole story, I have had swords that have that magic touch, beyond their paper performance, and a few lemons that by maths were good. Also one mans lemon could be anothers dream.
measurements are ok for reference, but some times only tell half the story.
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Owen Bush
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PostPosted: Fri 21 May, 2010 8:39 am    Post subject:         Reply with quote

Defining a sword from a couple of statistics is to me like defining a car by its weight and average speed.
Swords in reality are greatly different from one another , there usage and design differing being as different as the people using them .
to really understand a swords presence and behavior under use there are all sorts of things that come into play .Blade stiffness being one that has not really been mentioned . This has a huge impact on the feel of a sword . as does weight distribution . A blade with a very concave distal taper will behave very differently from one with a convex distal taper .both could have the same weight and pob .
Weigh and pob are just a couple of things that could hint to haw a sword might feel .
It has been my experience that in order to understand how a sword will behave and more importantly for a maker like myself exactly what I have to do to remake a sword that will behave in a similar way to a particular old one . all sorts of information is needed . In fact a full documentation only gets close .
Long swords on there own are a huge and varying subject . generalisations do not really stand against the variety that is out there .

All in my opinion of course .............

forging soul into steel .

www.owenbush.co.uk the home of bushfire forge school of smithing .
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Michael Edelson




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PostPosted: Fri 21 May, 2010 9:55 am    Post subject:         Reply with quote

To really understand a sword, you have to use it. Cut with it, thrust with it, parry with it, wind with it, etc. Numbers just give you a hint. As we have seen, some numbers mean more to some people than others, and that's okay. Ultimately it's just an intellectual exercise.
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P. Cha




PostPosted: Fri 21 May, 2010 10:10 am    Post subject:         Reply with quote

PoB alone doesn't tell you much. You need length and weight to get a BASIC view of how the the sword will handle. However that isn't the whole picture.

I'll give an example of two swords, a gen 2 black prince and an albion crecy.

The black prince has a PoB of 3 inches, 34 inch blade, 44 inch total and weight 3 lbs.

The crecy has a PoB of 4 inches, 35 inch blade, 44 inch total and weights 3 lbs 1 ounce.

Now according to the basic number, the gen 2 should be the faster sword as it weights less and as a closer PoB and a shorter blade. It isn't. The albion has superior mass distribution so it is quite a bit faster.
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Thom R.




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PostPosted: Fri 21 May, 2010 10:29 am    Post subject:         Reply with quote

Michael Edelson wrote:
To really understand a sword, you have to use it. Cut with it, thrust with it, parry with it, wind with it, etc. Numbers just give you a hint. As we have seen, some numbers mean more to some people than others, and that's okay. Ultimately it's just an intellectual exercise.


I think that sums it up well. One of the reasons I am a bit sensitive when I see people saying things with a gist of "the numbers don't matter" is that I am an engineer and I feel that culturally, at least here in the US, there is this push to "dumb everything down". e.g. how many cars today have an actual temperature gauge on the dash. Instead we now have warning lights..... although what it actually means when a warning light turns on is anyone's guess because nowhere in the manuals will you find the specs of wth it means or what kind of factor of safety is built in to the system or what margin of safety you have once the warning lights turn on. Heck these days there are even car manufacturers making cars with manual transmissions without tachometers which imho is just crazy.

I may have stated this here before in another one of our "sword geeky" threads but I am a big believer in measurement. The great thing about knowing the concepts of science and having measuring devices like the thermometer, or the scale, or the watt-hour meter is that they enable a person to see new aspects of their world Idea Idea that were not necessarily obvious before.

In fact my belief in the utility of measurement, and the habit of doing measurements, is so great that it is part of my personal interpretation of how progress works in the world. I believe the world has two aspects, physical (roughly nouns) and process (roughly verbs); the two are dually operating on one another, creating new objects/verbs through their interaction. e.g. a physical object "mercury" by means of a process "measuring length of a column" defines a new object named "temperature" which turns out to be useful for studying a new process "heating" etc. Therefore studying and quantifying measurable phenomena is a very very important path through which we learn and progress in our knowledge, as individuals, as a society and as a human race.

ok down off the soapbox now. Wink tr
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Glen A Cleeton




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PostPosted: Fri 21 May, 2010 11:07 am    Post subject:         Reply with quote

An oft revisited discussion that does occasionally bring new ideas to the table. Otoh, it seems like a different perspective of engineering wheels seems to always go back to some basics.

A page I had been browsing through again brought this section to mind and the data collection something any reviewer or statistician could include.

http://www.oakeshott.org/hsdp.html

I do agree that some basic numbers can point to some theoretical single number of rating but while prefering to judge each object on its own (subjective) merit or fault. I always go back to automotive handling differences and can only express that to my own preferences that the most "lively" are the ones with the most neutral and forgiving power to steerage ratio (adhesion would count in cars as well and might be important in including oversteer or understeer characteristics [traction in winding and binding]). To me, I always have to include the power source and impetus in my own favor of sword handling.

Something that was adopted and since discarded several times was the Don Nelson rating that was put forth to put a single number up as what a prospective owner might. I know I had posted it up in similar threads over the years but never really paid it much attention myself. Maybe some helpful soul will remember the old threads from Don but I'd have to search them out again myself. It was a brief Eureka for some at that time and others have seen it as useful since then but there has always been a lot more to the engineering dissertations and personal preferences that find the single number rating lacking in determining the best sword Wink Best at what ?8^)~ Oh my, here we go again
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Glen A Cleeton




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PostPosted: Fri 21 May, 2010 11:25 am    Post subject:         Reply with quote

Ah yes, here it is

Don's QuADSHaP

http://www.swordforum.com/forums/showthread.php?t=6821

Quote:
As you might recall, I am a bit of a numbers nut, and am always looking for better ways for numbers to tell us things about swords, particularly how "handy" the sword is.

A notion has been rattling around in my head for a few days now, and it finally took shape tonight.

I call it "Don's Quick And Dirty Sword Handiness Product".

The number yielded by this process is a quick'n'dirty value that tells the potential user/buyer of the sword, how "handy" the sword is when used with one hand.

I've run some numbers using some of the swords I have, and the values that popped out "seemed about right".

Here is the formula:

Wt. x BL x PoB / 1,000 = QuADSHaP

Wt: Wt of sword in ounces

BL: Blade Length in inches

PoB: Pay careful attention here - this is Point of Balance as measured from the foremost portion of the grip, that is, the location where the top of the hand would rest if shoved as far forward as possible against the guard. This would place this particular PoB about one-quarter inch further along than if it were measured from the tip-side portion of the guard.

1,000: Simply a constant to reduce the number to something easily "grab-able" by the mind.

Basically, the bigger the number produced, the less "handy" or less "maneuverable" the sword is with one hand. Naturally, when two hands are used, the dynamic of muscular control changes significantly, and all but the heaviest or clumsiest of swords become manageable.

Let's look at some examples from my "stable" of swords, plus one I'd like to get:

Sword -- Wt -- Bl Ln -- PoB -- QuADSHaP

A&A 12th Cent -- 59 -- 35.0 -- 6.8 -- 13.9

CAS CSA Saber -- 41 -- 32.9 -- 8.0 -- 10.8

AT Ranger -- 45 -- 36.0 -- 6.3 -- 10.1

A&A Ital 3-Rng Rapier -- 43 -- 37.0 -- 5.5 -- 8.8

AT XVIII Hvy -- 48 -- 32.5 -- 5.3 -- 8.2

AT DD1401 -- 40 -- 34.5 -- 5.8 -- 7.9

AT DS1503A -- 37 -- 33.8 -- 5.8 -- 7.2

AT MS1501 -- 35 -- 31.8 -- 5.0 -- 5.6

CAS Mort. Bskthlt -- 37 -- 32.9 -- 3.6 -- 4.4

What I see here in terms of the numerical handiness value, seems to mirror my subjective "feel" in how easily these swords are manipulatable by me, with one hand.

Let's look at some examples:

For example, my 12th C. Sword from A&A is a cutter deluxe, but is clearly the worst of my swords in a thrusting or fencing style dogfight, whereas my CAS Mortuary baskethilt, that balances closer to my hand, is somewhat light in weight, and has a shortish blade is the most agile.

Note that among the swords in general though that my beloved MS-1501 English Knightly Sword presents the second lowest value, and hence is quite maneuverable in comparison, which corresponds strongly with my recent ravings about how light this sword feels, and how surprisingly agile it is.

I admit that this is at best just a dirty approximation at attempting to quantify the complex variables that go into determining how a sword handles or feels, but the numbers that pop out, do seem to, as I said earlier, "feel about right".

I'm planning on getting a Christian Fletcher Type XVIII Heavy, and wanted to get some kind of sense of how this sword would heft, especially since it is a one-hander, and a heavy one at that (3-lbs).

These numbers tell me that this particular sword is going to be quite a chunk of steel, being harder to haul around than three of my hand-and-a-halfers. After swinging the DD1401 around with one hand for a while, and finding it not very pleasant really, I'm starting to rethink my plans on getting the XVIII Heavy.

Also note my CAS Confederate Cavalry Saber, a wall hanger of very untapered, thick steel. It feels unwieldy in my hands, unpleasantly so. Worse even than trying to fence with the "full-sized battle sword", the Sword of the Ranger. This is, oddly enough, accurately reflected in these quick'n'dirty "handiness" values.

This QuADSHaP is just a rough guide, but I am surprised really at how well it does given its simplicity and crudeness.

Don


~~~~~~~~~~~~

Cheers

GC
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Thom R.




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PostPosted: Fri 21 May, 2010 1:36 pm    Post subject:         Reply with quote

Yes a good one from Don! hence my post here several years ago where i showed that there is clearly a "central tendency " regarding blade lengths and weights that most modern swordmakers are using ..... this central tendency is the effect of cnc milling, with generally the same sized stock (0.25 inch) and the little bit of scatter in the data in the blade length/weight relationships that you see is due to different techniques regarding distal taper.



which makes me all the more impressed with a sword like the Albion Svante, or the Albion Gallowglass, both of which are rather uniquely different (on opposite ends of the weight/length scale) than the vast majority of production market swords (Svante and Gallowglass show as outliers above and below the other swords I have in the above graph)
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Glen A Cleeton




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PostPosted: Fri 21 May, 2010 2:21 pm    Post subject:         Reply with quote

It was during Don's discussions and then the thoughts of thicker stock and more concave or covex distals came to mind. Quite apparent on old period swords where thickness of even small swords start at the guard with a lot of beef, then reducing to near half that in the first few inches at the cog and then a more linear distal to the foible. It still varies a lot though. There was still quite a lag before Gus was even working with the thicker stock while the buzz words of low polar moment came to vouge.

I find myself still just working with one specific sword or another to get the best I am able to out of whatever the characteristics are. I do though find my own favorites from a random selection and go "hmmm, I like this one" in my own mind's eye. In appreciating that, rarely bothering to measure all the numbers. I found preferences of my own in accumulating a large group of spadroons. The simplest hilt of a favorite handler actually has a cog further out the blade than others with more hilt weight and closer cog.

Each genre for its own merits and use though.

GC
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Robert Subiaga Jr.





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PostPosted: Fri 21 May, 2010 3:26 pm    Post subject:         Reply with quote

Unfortunately this problem is, paradoxically, being overthought and underthought at the same time. This is not simply a problem of the mechanics of the sword alone but of the sword in conjunction with BIOmechanics.

The pivot point is not necessarily--or even usually--the wrist, certainly not the wrist alone. It can be primarily the shoulder, the elbow, the wrist, or any combination of two or three of these, which are all quite adjustable by the swordsman. Adapting the stroke in turn renders the point of inertia a minimal factor or even a non-factor, which is why many respondents have been saying it doesn't seem to matter to them.

However, the adjustment made can't change the fact of "feeling" a notable difference based on overall weight and balance point.

This is the ironic truth of physics: as often as not that more accurate, complex analysis means a distinction can be quantified--but doesn't really matter much!

Happy

Starting in a hollowed log of wood—some thousand miles up a river, with an infinitesimal prospect of returning! I ask myself "Why?" and the only echo is "damned fool!...the Devil drives...
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Timo Nieminen




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PostPosted: Sat 22 May, 2010 1:06 pm    Post subject:         Reply with quote

Robert Subiaga Jr. wrote:

The pivot point is not necessarily--or even usually--the wrist, certainly not the wrist alone. It can be primarily the shoulder, the elbow, the wrist, or any combination of two or three of these, which are all quite adjustable by the swordsman. Adapting the stroke in turn renders the point of inertia a minimal factor or even a non-factor, which is why many respondents have been saying it doesn't seem to matter to them.

However, the adjustment made can't change the fact of "feeling" a notable difference based on overall weight and balance point.


That the swing is complex, and the pivot point is not where one might naively think it is, seems to have become well-known in sport science. It was not always so, but the science of bats and rackets has advanced. But the science also matters more for bats and rackets - the top athletes are all skilled, fit, and physically suited to their sport, and a small improvement can mean a decisive advantage. In swordsmanship, especially the rather relaxed amateur swordsmanship we have today, the time and energy spent on engineering a modern optimum sword is unlikely to be the key to success; enough to just choose a "good" sword.

Still, the methodology of sports science is there for those who are interested. To analyse swings, get a high-speed camera, and analyse frame-by-frame. Find the instantaneous centre of rotation (which can, and certainly does in some cases, vary during the swing/cut). Short of this, all the numbers tell you is a summary of the handling properties of the sword, in a way that can be used to compare different swords even without the opportunity to handle them. (But you'd better have the opportunity to handle some swords with the numbers describing them available, or else you won't have any feeling for the numbers.

All you do when handling a sword is move it and rotate it. So all you need to describe its handling is its linear inertia and its rotational inertia - its mass and moment of inertia. This last one needs to be the moment of inertia about the centre of the rotational motion, so you want to know the centre of mass as well, since the location of the CoM relative to the centre of the rotation, and the MoI about the CoM, tells you the MoI about the centre of the rotation.

What is over-talked and under-thought is the importance of these in cutting, but that's another story.

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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Timo Nieminen




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PostPosted: Sat 22 May, 2010 1:34 pm    Post subject:         Reply with quote

Vincent Le Chevalier wrote:

I'm currently writing an article specifically about how to measure a sword for its handling. I still need to shoot some pictures illustrating the process, as Michael says finding the CoO is not really straightforward and the measurement is hard to accomplish unless someone shows you how to do.


Pendulum test is good, works well enough even holding the sword. Ideally, you want the sword suspended e.g. on a string. For a "standard" pendulum test, suspension at the bottom of the grip/top of the cross will work.

The waggle test gives the same result, needs more instruction/practice, needs less equipment (pendulum test needs at least either a pendulum or a stopwatch).

For the ultimate test, measure the moment of inertia about the CoM directly by suspending from a torsion pendulum. Not that bad for equipment, just need a wire and a clamp (or two), a stopwatch, and calibration (e.g., using a known rod). I haven't set up one of these yet, but have done this in the past on non-swords - 'tis easy.

For the ultimate measurement, measure the MoI tensor, not just the normal-to-the-sword component. Suspend the sword in both horizontal orientations, edge up or down, and edge sideways, and suspend vertically. Alas, for the swords where this will matter (i.e., highly curved swords), you might need to add something like a plank to the system to be able to clamp at the CoM when it isn't on the blade - needed to get both horizontal orientations.

MoI tensor measurement is a bit of overkill for most, but it might say something interesting, or even useful, about highly curved blades, especially on large heavy swords. In principle, you want to know the whole MoI tensor when the centre of the rotation isn't on the line of the blade (e.g., any cut where the hands are leading the point), but for a straight sword, the two horizontal-orientations give essentially the same number, and the vertical-orientation gives close to zero, in comparison.

"In addition to being efficient, all pole arms were quite nice to look at." - Cherney Berg, A hideous history of weapons, Collier 1963.
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