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James R.Fox




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PostPosted: Thu 06 Mar, 2008 9:41 pm    Post subject: How to find point of balance versis center of percussion.         Reply with quote

Gentlemen does anyone remember how to determine the point of balance of a blade versus its center of percussion? They Are differant,but how, and how they are determined I.'ve forgotten, and can't find my referece book on it either. It sticks in my mind that it was done by a pendulumn device used by sword cutlers when they were going to hilt the sword.. Often the bladesmith;blade polisher/grinder that did the final polish,shape and edge; and the guy who balanced it with the hilt were specialized experts,I know that.
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Vincent Le Chevalier




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PostPosted: Fri 07 Mar, 2008 12:55 am    Post subject: Re: How to find point of balance versis center of percussion         Reply with quote

James R.Fox wrote:
Gentlemen does anyone remember how to determine the point of balance of a blade versus its center of percussion?


Sure Happy In fact the matter is discussed more or less regularly on every forum about swords...

The links that appeared automagically in your post point to a page giving the usual sword-related meaning. I don't have much more to say about the center of gravity or point of balance, everyone agrees on the definition and it is easy to measure.

Now, the center of percussion... In common sword-related context it is associated to the node of vibration that appears on the blade. However, this is not coherent with its use in every other contexts, including baseball bats. This part of your post:
Quote:
It sticks in my mind that it was done by a pendulumn device used by sword cutlers when they were going to hilt the sword.

makes me think you have seen the other definition before, since it is indeed linked to pendulums. This page might be of help: http://www.kettering.edu/~drussell/bats-new/cop.html. The two first parts are general and true for swords.

If you fancy more reading about the relevance of either points for sword use, you can read two recent discussions on other forums:
- COP = bogus? over at SFI
- Sword Characteristics Vs Characterization (and a bit on CoP) on Michael Pearce's forum

Hope this helps

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James R.Fox




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PostPosted: Fri 07 Mar, 2008 2:39 am    Post subject:         Reply with quote

Vincent-It does indeed and now I remember where I saw it, which is Sir Richard burton's book on swords. I'll re-read it, but it seems to have been a simple method of finding the CoP.
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Bill Tsafa




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PostPosted: Fri 07 Mar, 2008 6:06 am    Post subject:         Reply with quote

I believe determining the COP is as easy as holding the sword by the handle and banging it on the flat near the hilt. The sword blade will vibrate. As you look up the blade you will notice a spot that has almost no vibration, that is you COP. In fighting with sword and shield, I find it has no real use. What part of the sword I hit with has more to do with my position at any moment vs my opponent's position. Not getting hit myself and landing "any" good blow is more of a concern then landing the perfect blow. I am generally aware that if I am going to strike near the tip, I need to give the sword more velocity. If I am in a close position and strike with the forte, I need to punch the sword out to make up for the lack of speed since the forte travels slower then the tip. Punching with the forte offsets the kick that you would get if you just tried to cut normally and land on the forte.
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Last edited by Bill Tsafa on Fri 07 Mar, 2008 1:20 pm; edited 1 time in total
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James R.Fox




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PostPosted: Fri 07 Mar, 2008 10:26 am    Post subject:         Reply with quote

Thank you-I think that covers it. I believe Burton's book was talking more about a cutler finding the proper weight of hilt on a sword he was working on, and you are talking about how to fight in practice with that sword.
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Vincent Le Chevalier




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PostPosted: Fri 07 Mar, 2008 11:10 am    Post subject:         Reply with quote

James R.Fox wrote:
I believe Burton's book was talking more about a cutler finding the proper weight of hilt on a sword he was working on, and you are talking about how to fight in practice with that sword.


But both should be related, since obviously the weight you put on the hilt depends on what you expect to do with the sword (if there was a universal best answer to this we wouldn't be seeing so many types of swords balanced differently)...

Vassilis observations highlight the problem with the CoP considered as a node of vibration: it is neither the general best location of impact, nor a point of particular significance for the balance of the sword. The other definition of the CoP solves at least the second problem, provided that the reference point is explicit.

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Ed Toton




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PostPosted: Fri 07 Mar, 2008 5:13 pm    Post subject:         Reply with quote

If you're talking about measuring the characteristics of a completed sword, then this is something we've attempted to elaborate on a little but on swordwiki as well:

http://swordwiki.org/wiki/Center_of_Percussion

http://swordwiki.org/wiki/Point_of_Balance

http://swordwiki.org/wiki/Pivot_Point

I'm not sure what would have been used historically by cutlers while assembling swords.

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Shawn Shaw




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PostPosted: Fri 07 Mar, 2008 7:24 pm    Post subject:         Reply with quote

I have a related question. Namely, how do you determine the balance point of a sword when you are making it? More specifically, you have a blade blank and the various hilt furniture/grip/etc. How do you determine how heavy the hilt components need to be to get a good balance point? The only reasonable way I can think of is to start with some excess mass in the hilt components and then trim them down until you get the balance right. I suppose you could do the same on the blade side of thing but, generally, your blade is just about done when you mount the hilt, so you probably don't have as much leeway in adjusting the blade.

Any suggestions/ideas?
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Chad Arnow
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PostPosted: Fri 07 Mar, 2008 8:00 pm    Post subject:         Reply with quote

Shawn Shaw wrote:
I have a related question. Namely, how do you determine the balance point of a sword when you are making it? More specifically, you have a blade blank and the various hilt furniture/grip/etc. How do you determine how heavy the hilt components need to be to get a good balance point? The only reasonable way I can think of is to start with some excess mass in the hilt components and then trim them down until you get the balance right. I suppose you could do the same on the blade side of thing but, generally, your blade is just about done when you mount the hilt, so you probably don't have as much leeway in adjusting the blade.

Any suggestions/ideas?


Here's a spotlight topic that deals with that concept: http://www.myArmoury.com/talk/viewtopic.php?t=3189

Happy

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Craig Johnson
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PostPosted: Fri 07 Mar, 2008 8:51 pm    Post subject: CoP and Balance figuring Oh my!         Reply with quote

Hi Guys

As I was about to type a response about the Balance adjustments Chad, "Keeper of Great Posts", posted the link to the discussion we had a while ago and there is not a great deal to add to that to start with and if you read that and have queries please holler and we can address them.

After reading several of Vincent's various threads and looking over his great amount of work and discussion on this I feel that we should all rethink the use of CoP to equate to the blade node as we have in the past. It can define a spot on a sword that does have value in discussions of the physics of the sword whether that is in the mathematical sense or the practical sense. The use of CoP as other studies of physical objects use the term will allow our discussions to be more accessible to those outside our field of study and allow those other disciplines to consider our commentary without us having to explain why we have a different definition for the term than everyone else. This will hopefully allow others to view our discussions with the seriousness and contemplation they deserve.

I would guess that Vincent and others would agree with this and it is something we can all work on to make our research more accessible and clear to the none sword world.

To quote Vincent’s commentary that I think explains it quite well

“The Center of Percussion, in the meaning common to all other contexts, is something purely related to the rigid body dynamics.

Assume you have an object such as a sword, suspended so that it can only rotate around one specific reference point. If you strike the object somewhere along its length, it will obviously rotate around this point. But at the time of the impact, forces will be exerted on the pivot, either pushing or pulling it. It can be proven that there is a specific point of impact where no force is propagated back to the pivot. This is the Center of Percussion associated to the pivot.”

While I have worked hard to change many aspects of what we know and use to describe swords over the years, I realize this may not occur but I for one will being doing what I can to adjust to a more accurate description of what a sword is and does.

Best
Craig
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Vincent Le Chevalier




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PostPosted: Sat 08 Mar, 2008 4:20 am    Post subject:         Reply with quote

Well unsurprisingly I completely agree with you Craig... Actually I'm honored to be quoted by you on this Happy Credit should mainly go to Kyle H. at SFI who was the one that originally insisted on using the more accepted meaning. I have been more concerned myself with how we use these points to understand swords than by how we call them...

Problem is that we'll need a dictionnary to read the old threads now Happy For example, in the discussion Chad linked to:

The Center of Percussion should be now refered to as the blade vibration node (as Peter Johnsson was already doing, by the way). The 'pivot points' Peter Johnsson describes are actually centers of percussion associated to various reference points on the grip. I'm unsure of how he calls them these days, but I'm pretty sure he is not using the standard denomination found in other fields.

In most of the past discussions I used the same approach, i.e. I used the terms center of percussion and pivot points, and then increasingly blade node and pivot points. But I started to be bothered by these 'pivot points' (that are actually centers of percussion, but the term was taken Wink ) because when there is an actual pivot point at stake (an articulation that forces the object to rotate around it), you start to speak of the pivot point associated to the pivot point, which is obviously a total mess Big Grin

Unfortunately, there are properties of these points that are relevant to swords, but that are not covered by the term center of percussion (link to pendulums, reciprocity, link to mass distribution). Also, we are interested in several of these centers of percussion (as explained by Peter Johnsson), so we'll have to loose the habit of using the name to refer to a single absolute point. I don't know how difficult it will be...

Regards

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Peter Bosman




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PostPosted: Sat 08 Mar, 2008 5:33 am    Post subject:         Reply with quote

Personally I think the concept of nodes and use of this term is most correct.
Putting the articles of Michael Pearce and Peter Johanson together with the extensive and highly enlightening ARMA article of George Turner makes it perfectly clear that the behaviour of a sword is heavily influanced by ' virtual' points not actually located in/on the sword. The word 'node' links to the concept of waves and that is what a lot is about, so I like that Big Grin

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Craig Johnson
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PostPosted: Sat 08 Mar, 2008 6:44 am    Post subject: HI Peter and Vincent         Reply with quote

Morning Guys

I felt the same way as you Peter until recently. After watching this discussion over the years and participating when my meager knowledge could contribute I decided to reassess as much as I could with a desire to more fully integrate my practical knowledge with that of scientific community that studied these types of things. It could continue as it is now (and will as there is momentum behind a shared belief or terminology that resides in any population and there is no decree strong enough to change that) but I thought back over the years and remembered my struggles to inform customers that "no my swords where not to light, a sword should not weight ten pounds" or that "a fuller has nothing to do with letting blood" or no "a Katana could not cut through any other sword". These seem outrageous I know, but I have spent huge amounts of time educating people out of these beliefs in my career. So to tie myself down by not being more accurate and with a clearer understanding of how a sword works would mean I had lost something in my drive to understand. I am not ready for that as yet Happy

Vincent I should have mentioned Kyle H. as well as his comments are so well stated and clear. In fact I need to quote him here, as this was one of the key points I acquired through the discussions. The words in parenthesis are mine to clarify what I believe to be Kyle’s meaning.

"In terms of the (historical) fiasco with sword terminology, I think I have a solution that should make everyone more or less happy. Since many sword smiths now list various parameters about their blades, for cases where the "CoP" and "node of vibration" are effectively in the same location, why not simply list "CoP & Node" as one number? This serves two functions: The first is that regardless of what definition of "CoP" you use, you can recognize that the thing listed under "CoP & Node" will have the number you're looking for, which will cut back on initial confusion. The second is that it raises awareness that there are, in fact, two independent points here of interest. I get the sense that many individuals simply aren't aware that "hand shock" is the product of two separate sources, and highly respected individuals in the sword community, like sword vendors, can do a lot to help make people aware of what these points actually are, and why they matter. Likewise, it would help if websites changed their definitions of CoP to match the definitions proposed initially by those studying the oscillations of pendulums and swords in the mid-1600's (aka the physicists). Here's a semi-formal example:

Center of Percussion: the point where a perpendicular impact to the blade will produce rotational and translational forces that will cancel out at some other point of interest, causing the blade to pivot about that point. Usually this other point of interest is taken to be the location of the hand on the sword.

Those of us who are more mathematically inclined should likewise do their part by explaining what the CoP and Node actually are, whenever it comes up, bearing in mind that clarity is as important as correctness (with the former often being harder than the latter.)"

Peter I would agree that we can not discard out right what has been done in the past the articles by Peter and Tinker are crucial to understanding swords in fact we would not be having this discussion if it was not for them. I as well as they are neither a structural engineer nor a physicists. Correct me if I am wrong guys Happy So in these technical discussions the terminology used was what was to hand and mind, this should not be discarded but can be improved to describe more clearly what we are trying to communicate.

It is to much to say we have to rewrite everything but to continue our growth in understanding would it not be better to define what we know as clearly as possible. Something that was assumed to have one casual element but can clearly be demonstrated as having two should be recognized and appreciated for the increase in knowledge on our part that it is.

For many this maybe so fine a difference as to be meaningless, that is fine. For me personally I would like to have as full an understanding as my poor brain will allow. Which I fear is less than I think it is Laughing Out Loud

Keep well
Craig
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Jared Smith




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PostPosted: Sat 08 Mar, 2008 8:02 am    Post subject: Re: CoP and Balance figuring Oh my!         Reply with quote

Craig Johnson wrote:
Hi Guys

The use of CoP as other studies of physical objects use the term will allow our discussions to be more accessible to those outside our field of study and allow those other disciplines to consider our commentary without us having to explain why we have a different definition for the term than everyone else. This will hopefully allow others to view our discussions with the seriousness and contemplation they deserve.


I agree with you Craig. There are lots of similar perspectives here. I am an engineer and occasionally have to use the term as the scientific community expects it to be used. The CoP should be close to the primary vibration node, or else the sword may be inefficient, or even unpleasant, to use. The simple fact is the vibrational node does not have to coincide with CoP, and when measuring with precision (mm on bats and such) seldom are in exactly the same place. Sweet spot is also subjective according to an individual's grip method. When a bat manufacturer tests (hundreds of trial hits by athletes) a tournament bat it often turns out that sweet spot, CoP, and vibrational nodes are judged to be three separate things. Saying that they are the same thing, or that locating the primary vibration node along the flat of the blade positively identifies CoP is a generalization that satisfies those who are content to know "approximately where it is" on a nice handling straight blade. It would be more valid to point out that for any straight (not having much taper in profile or thickness) rod, the CoP is 2/3 of its length away from the grip/ pivot point. If the blade or rod has lots of taper (getting smaller towards the tip) then the CoP moves closer to the grip. Without touching the blade, one with a little bit of practice or experience through calculation should be able to estimate CoP to within an inch just by looking at the sword.

Vincent's model of sword harmonics somewhat illustrates how one of the nodes for a typical flat type cross section blade falls out at a location similar to the CoP. It would be nice to see some other cases (heavy pommel/ heavy guard, etc.) To some degree, the nodes can be shifted with furniture, fullers, etc. I suspect a tuck or bizzare cross section could turn out significantly different! http://www.myArmoury.com/talk/viewtopic.php?t...ight=model

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Angus Trim




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PostPosted: Sat 08 Mar, 2008 11:31 am    Post subject: Re: HI Peter and Vincent         Reply with quote

Craig Johnson wrote:
Morning Guys

"In terms of the (historical) fiasco with sword terminology, I think I have a solution that should make everyone more or less happy. Since many sword smiths now list various parameters about their blades, for cases where the "CoP" and "node of vibration" are effectively in the same location, why not simply list "CoP & Node" as one number? This serves two functions: The first is that regardless of what definition of "CoP" you use, you can recognize that the thing listed under "CoP & Node" will have the number you're looking for, which will cut back on initial confusion. The second is that it raises awareness that there are, in fact, two independent points here of interest. I get the sense that many individuals simply aren't aware that "hand shock" is the product of two separate sources, and highly respected individuals in the sword community, like sword vendors, can do a lot to help make people aware of what these points actually are, and why they matter. Likewise, it would help if websites changed their definitions of CoP to match the definitions proposed initially by those studying the oscillations of pendulums and swords in the mid-1600's (aka the physicists). Here's a semi-formal example:

Center of Percussion: the point where a perpendicular impact to the blade will produce rotational and translational forces that will cancel out at some other point of interest, causing the blade to pivot about that point. Usually this other point of interest is taken to be the location of the hand on the sword.

Those of us who are more mathematically inclined should likewise do their part by explaining what the CoP and Node actually are, whenever it comes up, bearing in mind that clarity is as important as correctness (with the former often being harder than the latter.)"

Peter I would agree that we can not discard out right what has been done in the past the articles by Peter and Tinker are crucial to understanding swords in fact we would not be having this discussion if it was not for them. I as well as they are neither a structural engineer nor a physicists. Correct me if I am wrong guys Happy So in these technical discussions the terminology used was what was to hand and mind, this should not be discarded but can be improved to describe more clearly what we are trying to communicate.

It is to much to say we have to rewrite everything but to continue our growth in understanding would it not be better to define what we know as clearly as possible. Something that was assumed to have one casual element but can clearly be demonstrated as having two should be recognized and appreciated for the increase in knowledge on our part that it is.

For many this maybe so fine a difference as to be meaningless, that is fine. For me personally I would like to have as full an understanding as my poor brain will allow. Which I fear is less than I think it is Laughing Out Loud

Keep well
Craig


The reason you see the term "COP" being listed again, is that potential customers ask about it.

Separating the terms CoP and Blade Node has already happened in discussions, yet in practice, the two are always found in the same location . I can't think of one time I've found different, though I suppose its theoretically possible. I don't want to handle the sword that exhibits this though....{separate locations}

The thing is, a medieval type, double edged sword is not really all that rigid, most of the time. And the exact placement of the nodes can be influenced by the amount of distal taper, the character of distal taper, profile taper, and character of profile taper, length of tang, width of tang, and tapers of tang, blade geometry { crossection, thickness at edge, etc}......

Then you have some interesting variables......... for instance.......why does a double fuller arrangement quite often move the blade node down the blade an inch, from where it would be on an identical blade with just one fuller?

The next is, that with the modern choice of targets, the location of the node is almost immaterial except in a sword geek's interest. In reality, with soft targets like water filled plastic bottles, pool noodles, and tatami mats, the sword blade should be able to cut just fine tipwards from the blade node {or cop}.......

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Jared Smith




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PostPosted: Sat 08 Mar, 2008 12:03 pm    Post subject:         Reply with quote

I have an earnest question; how do you, the manufacturer, find this blade node or CoP?

If one looks at the Albion article on sword Dynamics http://www.albion-swords.com/articles/images/sword-dynamics.pdf
there is an illustration of a hilted and unhilted blade. The hilted blade indicates a "hilt node 2" that I would assume to be very close to the pivot point of the sword if flexing the wrist and rotating it.

From a kinematics perspective, in the hilted sword, there is a CoP somewhere down by what the illustration calls BN2 or FP2. If we drilled a hole through the location "hilt node 2" (HN2) and allowed the sword to swing on a metal pin like a pendulum, in direction of cuttting, there is a spot where if the blade struck another pendulum, the sword would stop and transfer all of its energy into the struck pendulum. Optimally, the pommel would minimize any "kcik" or shock near HN2. In such as case, that spot found through impact and transfer of the energy is a scientific CoP that is specific only for this case where HN2 was arbitrarily chosen as a pivot point.

In practical terms, there is no exact pivot point that perfectly models all different styles of cuts (Oberhaue, Zornhow, etc.) and various grips (hand and a half versus single, etc.) The sword maker has to impart the final handling according to his experience, and tweaking to their own preference. I accept your preference and experience. However, I would like to know what these statistics routinely published to a precision of 0.01" actually are trying to convey!

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PostPosted: Sat 08 Mar, 2008 12:53 pm    Post subject:         Reply with quote

Jared Smith wrote:
I have an earnest question; how do you, the manufacturer, find this blade node or CoP?

If one looks at the Albion article on sword Dynamics http://www.albion-swords.com/articles/images/sword-dynamics.pdf
there is an illustration of a hilted and unhilted blade. The hilted blade indicates a "hilt node 2" that I would assume to be very close to the pivot point of the sword if flexing the wrist and rotating it.

From a kinematics perspective, in the hilted sword, there is a CoP somewhere down by what the illustration calls BN2 or FP2. If we drilled a hole through the location "hilt node 2" (HN2) and allowed the sword to swing on a metal pin like a pendulum, in direction of cuttting, there is a spot where if the blade struck another pendulum, the sword would stop and transfer all of its energy into the struck pendulum. Optimally, the pommel would minimize any "kcik" or shock near HN2. In such as case, that spot found through impact and transfer of the energy is a scientific CoP that is specific only for this case where HN2 was arbitrarily chosen as a pivot point.

In practical terms, there is no exact pivot point that perfectly models all different styles of cuts (Oberhaue, Zornhow, etc.) and various grips (hand and a half versus single, etc.) The sword maker has to impart the final handling according to his experience, and tweaking to their own preference. I accept your preference and experience. However, I would like to know what these statistics routinely published to a precision of 0.01" actually are trying to convey!


Hi Jared

If you're addressing this to me, I'm not sure I really understand. I don't really worry as much about cop as I used to.....

Back in the day, when I was pretty new at all this, I used 1/4 inch plywood to cut into, to test all this. This is where the base of my knowledge really came from. Tinker added to it with his talk of "harmonic balance"... but for me, it was this cutting action into the 1/4 inch plywood, how deep the blade bit cutting with which part of the blade, and the action of the blade when the cut stopped abrubtly.

This, as well as certain handling characteristics I was looking for, is what most influenced my early designs. In those days I could give you a real good idea of why and what I was looking for in relation to the CoP.

Then I went to my first WMA event, the second Livermore {put on by Brian Price}. Here I met some real knowledgeable longsword guys, Bob Charron, and Christian Tobler. Here it was that I found out I still had a lot to learn on how certain swords needed to handle vis a vis certain martial arts.

I also met two guys attending this event, who also happened to work at Livermore. Discussing the node stuff, I wound up picking up a few more terms that became more in vogue over the next year, things like demi-nodes.

Over the next six months, I wound up finding out, thru experience, and feedback, that all of this was related. Worrying solely about the cop meant ignoring the way a blade handles opposition, for instance. Its all related.

Swords don't really work like baseball bats or tennis rackets. Yeah, there's some similarities, but mainly swords are unique. And sharp swords react just a bit differently than blunts. Oddly enough......

So...... I can't tell you what you're asking {if I understand it right}..... Different swords will have different requirements, and one will wind up compromising one thing to make another stand out.

Is the CoP important? To some customers, but I think in terms of the nodes. And not just the two nodes that are most commonly referred to.

I hate to use the term "lining up" to refer to the placement of the nodes and demi-nodes, but I can't think of another term. Depends on what I'm trying to accomplish, and what the sword will be intended for.

A bare blade will likely have the "blade node" pretty close to where it will be when the sword is mounted. But frequently, the node that becomes the "handle node" will be an inch or two actually on the blade. Its not until mounted, that the node gets "pulled" onto the tang.

In discussing cop though, if its just the main blade node you're looking for, its almost always close to the 2/3 spot of the blade, measured from the cross to the tip {on a double edged blade}. There are some heavily tapered blades {like some XVs} that may have the cop closer to the 1/2 way point, but 2/3 is most common. Some single edged blades, can have the cop out to 3/4......

The blade node is only a part of the harmonious whole...........

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Vincent Le Chevalier




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PostPosted: Sat 08 Mar, 2008 1:09 pm    Post subject: Re: HI Peter and Vincent         Reply with quote

Hi Gus!

Angus Trim wrote:
Separating the terms CoP and Blade Node has already happened in discussions, yet in practice, the two are always found in the same location . I can't think of one time I've found different, though I suppose its theoretically possible. I don't want to handle the sword that exhibits this though....{separate locations}


The problem I have with what you are saying (and that's what Jared is also talking about if I'm not mistaken) is that, when using CoP with the definition from other fields that Craig quoted earlier, the location of the CoP changes according to which point of reference you choose. If you take the picture of the mounted sword in the document linked to by Jared:
- if the reference point is AP, the CoP is AP2
- if the reference point is FP, the CoP is FP2
- if the reference point is HN2, the CoP *could* be BN2, or something near. No way to know without accurately measuring...

I'm nearly certain the blade node is the CoP of some point of the sword. I'm quite sure this point should be in the hilt. But where exactly on the hilt is it? Which point of reference are you choosing that allows you to say that the CoP and the blade node are the same?

I think, and you are quite welcome to correct me if I'm wrong, that you use CoP with the meaning 'place most efficient when cutting against hard targets' instead. It is not what is discussed here, nothing in the definition says it should be the best place to cut anything... and this is quite hard to measure in an objective way anyhow. In other words it can tell us little about the properties of the sword on its own.

On the contrary, having a measure of one reference point *and* its CoP gives the moment of inertia, which is the key to all the movements involving rotations. The vibration nodes won't give that with any accuracy. That's the difference.

--
Vincent
Ensis Sub Caelo
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Jared Smith




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PostPosted: Sat 08 Mar, 2008 1:27 pm    Post subject:         Reply with quote

Yes Vincent, that is pretty much what I am trying to convey.
I have total confidence in established makers to establish some point on the blade as having great significance. That said, the way that consumers wield the sword will always result in a variety of CoP's. Bat makers refrain from publishing a CoP, and instead mark a region about 3" to 4" long (75mm to 100mm) as a place where it is a good idea to make hard contact strikes. Within that region, you will generally find several scientifically specific traits (CoP as is very specific to grip, acoustic sweet spot, and a vibrational sweet spot....all 3 being distinctly different.) CoP being defined to within 0.01" is basically not plausible unless you define an ideal grip and form of rotation to within the same tolerances. The sweet spot marked on a bat does have a specific center, which usually does not conform exactly to any of the three quantifiable measurements.

Absence of evidence is not necessarily evidence of absence!
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Angus Trim




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PostPosted: Sat 08 Mar, 2008 1:38 pm    Post subject: Re: HI Peter and Vincent         Reply with quote

Vincent Le Chevalier wrote:
Hi Gus!

Angus Trim wrote:
Separating the terms CoP and Blade Node has already happened in discussions, yet in practice, the two are always found in the same location . I can't think of one time I've found different, though I suppose its theoretically possible. I don't want to handle the sword that exhibits this though....{separate locations}


The problem I have with what you are saying (and that's what Jared is also talking about if I'm not mistaken) is that, when using CoP with the definition from other fields that Craig quoted earlier, the location of the CoP changes according to which point of reference you choose. If you take the picture of the mounted sword in the document linked to by Jared:
- if the reference point is AP, the CoP is AP2
- if the reference point is FP, the CoP is FP2
- if the reference point is HN2, the CoP *could* be BN2, or something near. No way to know without accurately measuring...

I'm nearly certain the blade node is the CoP of some point of the sword. I'm quite sure this point should be in the hilt. But where exactly on the hilt is it? Which point of reference are you choosing that allows you to say that the CoP and the blade node are the same?

I think, and you are quite welcome to correct me if I'm wrong, that you use CoP with the meaning 'place most efficient when cutting against hard targets' instead. It is not what is discussed here, nothing in the definition says it should be the best place to cut anything... and this is quite hard to measure in an objective way anyhow. In other words it can tell us little about the properties of the sword on its own.

On the contrary, having a measure of one reference point *and* its CoP gives the moment of inertia, which is the key to all the movements involving rotations. The vibration nodes won't give that with any accuracy. That's the difference.


Hi Vincent

I'm not going to correct you, because at least in this conversation I think we're talking about two different things. I'm not certain exactly what the original question was about, but if it was the CoP as originally talked about, since the 19th century, then the blade node is it. If not, then it could be the theoretical point that you're talking about.

Since a sword is meant to be used with a hand on the grip, and a single hand sword is likely to have said hand against the guard, that's how I reference things. I really don't think, for instance, that an opponent is going to stand there and let you drop the sword on his head, at the balance point, for instance, referencing another such converation. Yes, I can understand someone wanting to know that, but I don't think a sword is going to be used that way......

Where the theoretical "COP" is on a blade? I don't know, I'm not sure I care frankly. Today, when I get involved in these conversations, its usually to try and bring things to the practical again. If you're cutting thick cardboard tubes, where's the best spot on the blade to use? If you're cutting tatami, where's the best spot on the blade to use? How does this affect the martial use of the sword? Etc.........

No, I'm not going to correct you Vincent, just throwing another view on this........

swords are fun
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