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Vincent Le Chevalier




Location: Paris, France
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PostPosted: Fri 31 Mar, 2017 11:54 am    Post subject: Documenting the dynamics of swords         Reply with quote

Hello all,

During the preparation of the exhibit 'The Sword - Form & Thought', Peter Johnsson and myself worked on a tool that made it easier to document and display the dynamic balance of swords. We are finally ready to share it with the community at large!

You can read more about its context and principles on this introduction page. Then you can use the tool itself, with the help of the more detailed walkthrough.

I hope many people will enjoy working with it! If you have any question about it, do not hesistate to ask.



Best regards,

--
Vincent
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Thomas Riley





Joined: 11 Jul 2014

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PostPosted: Fri 31 Mar, 2017 12:21 pm    Post subject:         Reply with quote

I have been eagerly awaiting this! Thank you!
Dum Spiro Spero, Dum Spiro Scio
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Fisher Lobdell




Location: Kansas city
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PostPosted: Fri 31 Mar, 2017 4:02 pm    Post subject:         Reply with quote

All vendors and manufacturers should provide a cart like this with every sword.
1 Peter 5:8 - Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:

Absence of evidence is not necessarily the evedence of
Absence. Ewart Oakeshotte.
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Fisher Lobdell




Location: Kansas city
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PostPosted: Fri 31 Mar, 2017 4:50 pm    Post subject:         Reply with quote

The vibration nodes you are putting on the diagram are in the plain of the flat. Which is less important than the vibration nodes in the plain of the EDGE I believe, when it comes to force transferred in the cut. Though the nodes for the flat are extremely important.
The only person I have heard mention this is, Matt Easton.
But Is there an accurate way to measure the node in the plain of the edge, Other than hitting a piece of wood and feeling where it is?
I would really love to see this in the diagram. Big Grin

1 Peter 5:8 - Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:

Absence of evidence is not necessarily the evedence of
Absence. Ewart Oakeshotte.
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Timo Nieminen




Location: Brisbane, Australia
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PostPosted: Fri 31 Mar, 2017 5:17 pm    Post subject:         Reply with quote

Fisher Lobdell wrote:
But Is there an accurate way to measure the node in the plain of the edge, Other than hitting a piece of wood and feeling where it is?


I can't think of any easy way to measure it. One problem is that if you hit the edge to excite vibrations, some of that will go into vibrations in the plane of the flat. Because the blade is much less stiff that way, those vibrations are likely to be large enough to mask the edge-plane vibrations. (Without this, it would be easy enough with high-speed video.)

I don't think you'll accurately find it by hitting a piece of wood, either. The change in reaction force on the hand when hitting at or away from the "real" centre of percussion (AKA the pivot point, as found by the waggle test) is very feelable and will probably mask the feeling of edge-plane vibrations.

"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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Bram Verbeek





Joined: 27 Mar 2007

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PostPosted: Sat 01 Apr, 2017 12:02 am    Post subject:         Reply with quote

I will use this on everything. Expect graphs of crowbars, spades, LARP swords and, if they stay stationary, cats. Just for reference of course.
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Vincent Le Chevalier




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PostPosted: Sat 01 Apr, 2017 12:02 am    Post subject:         Reply with quote

I have actually thought about edge to edge nodes a little bit Happy Some remarks:

  • As Timo points out, they are quite hard to measure. Most swords are stiff enough edge to edge that the motion will be tiny, and any sound made will probably be masked by the flat-to-flat higher modes. It is very hard to stimulate only edge-to-edge vibrations.
  • Functionally, I'm not sure they have a noticeable effect. In handling you will never notice the vibrations, and in cutting the vibrations are not detrimental, you only get a small oscillation in the force applied on the edge. Flat-to-flat vibrations, on the other hand, can increase friction or disturb edge alignment (or at least they can be related to these).
  • I have actually been simulating swords with a finite element method, which bypasses the need to measure. It can be shown with this that the nodes are indeed different in the two planes. However they are often not that different, unless you have a sword with a strange profile (rat-tail tang) or very evolutive fullering. The nodes of the primary mode of vibration are heavily influenced by mass distribution, which is the same in both planes.

For all these reasons, I don't think it is useful to focus on edge-to-edge vibrations in the current state of our knowledge and methods.

Best,

--
Vincent
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Guillaume Vauthier




Location: France
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PostPosted: Sat 01 Apr, 2017 1:57 am    Post subject:         Reply with quote

Wow, this is so cool! Thanks for that. I guess I'll try it extremely soon Big Grin
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Fisher Lobdell




Location: Kansas city
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PostPosted: Sat 01 Apr, 2017 11:17 pm    Post subject:         Reply with quote

I just thought I'd mention it. Happy I personally am more focused on pivot points.
1 Peter 5:8 - Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:

Absence of evidence is not necessarily the evedence of
Absence. Ewart Oakeshotte.
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Bram Verbeek





Joined: 27 Mar 2007

Posts: 217

PostPosted: Sun 02 Apr, 2017 12:45 am    Post subject:         Reply with quote

Bram Verbeek wrote:
I will use this on everything. Expect graphs of crowbars, spades, LARP swords and, if they stay stationary, cats. Just for reference of course.


I have the following things lined up (in rough order of seriousness), which I will test next week (this weekend was a little short).

Hanwei Tinker Bastard sword with fuller
1930's long bayonet (about 50cm total length)
Cold steel kukri
One handed modern axe
big file of about 50cm (that I still want to turn into a blade in the future)
Crowbar
one handed LAPR sword with carbon core
one handed LARP sword with fiberglass core
two handed LARP sword with carbon core
two norwegian forest cats (thogh getting vibration nodes with all the purring might prove challenging)

I'll try to get my hands on a flat iron bar of over 1m length, as reference for a basically shapeless piece of steel.
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Alan Gideon




Location: Virginia
Joined: 30 Jan 2012

Posts: 3

PostPosted: Sun 02 Apr, 2017 12:39 pm    Post subject: Experimental Protocol         Reply with quote

Bram Verbeek wrote:
Bram Verbeek wrote:
I will use this on everything. Expect graphs of crowbars, spades, LARP swords and, if they stay stationary, cats. Just for reference of course.


I have the following things lined up (in rough order of seriousness), which I will test next week (this weekend was a little short).

Hanwei Tinker Bastard sword with fuller
1930's long bayonet (about 50cm total length)
Cold steel kukri
One handed modern axe
big file of about 50cm (that I still want to turn into a blade in the future)
Crowbar
one handed LAPR sword with carbon core
one handed LARP sword with fiberglass core
two handed LARP sword with carbon core
two norwegian forest cats (thogh getting vibration nodes with all the purring might prove challenging)

I'll try to get my hands on a flat iron bar of over 1m length, as reference for a basically shapeless piece of steel.


First, thanks to Vincent for pushing this idea of discussing swords in terms of quantitative data, rather than "it felt good" and to you for adding to the database. As an engineer, one thing that stands out though, is that for the numbers to have value, one to another, we need repeatable protocols: Accuracy of static length measurements (+/- 0.5mm, perhaps? Mass (+/- 1 gram?) And how does a person quantify the degree to which the grip is pinched when trying to determine the pivot points and blade vibration node? My first thought would be to have multiple people in your circle of friends each make multiple tries at this as a way of eliminating measurement bias. Yes, your group could be consistently heavy-handed, resulting in very fuzzy answers, but it's an idea.
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Vincent Le Chevalier




Location: Paris, France
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PostPosted: Sun 02 Apr, 2017 1:09 pm    Post subject: Re: Experimental Protocol         Reply with quote

Alan Gideon wrote:

First, thanks to Vincent for pushing this idea of discussing swords in terms of quantitative data, rather than "it felt good" and to you for adding to the database. As an engineer, one thing that stands out though, is that for the numbers to have value, one to another, we need repeatable protocols: Accuracy of static length measurements (+/- 0.5mm, perhaps? Mass (+/- 1 gram?) And how does a person quantify the degree to which the grip is pinched when trying to determine the pivot points and blade vibration node? My first thought would be to have multiple people in your circle of friends each make multiple tries at this as a way of eliminating measurement bias. Yes, your group could be consistently heavy-handed, resulting in very fuzzy answers, but it's an idea.

Hi Alan,
I agree that a further step would be to add an accuracy value to all the measurements. For length and mass, easy enough. For nodes and pivot points... quite hard. One of the goals of taking several pairs of pivot points is precisely to assess the accuracy. For the nodes, you have to estimate based on what you've seen. The blade node is often better defined - thin blade, and a bigger amplitude. The hilt node can be a lot harder to locate with accuracy.

The idea with the correct waggle test is that the observed result does not depend on the user that much. But you have to learn not to pinch too hard, and yet waggle the sword with a high enough frequency. Heavy-handed users will probably not get consistent pairs from several locations.

Regards,

--
Vincent
Ensis Sub Caelo
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Fisher Lobdell




Location: Kansas city
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Reading list: 14 books

Posts: 65

PostPosted: Sun 02 Apr, 2017 9:45 pm    Post subject:         Reply with quote

Something I thought of is to hold the sword with some sort of callipers for accuracy in the waggle test.
1 Peter 5:8 - Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:

Absence of evidence is not necessarily the evedence of
Absence. Ewart Oakeshotte.
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Peter Johnsson
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PostPosted: Mon 03 Apr, 2017 10:26 am    Post subject:         Reply with quote

Any tool for doing the waggle test must be capable of taking both fully mounted swords and the naked tang of well preserved originals. And do this without leaving any marks. Such a device must also be so simple in construction that it can be built by all who are interested in taking this kind of measurements in a standardised way.
If everyone will use his or her own tool we still have a situation with data that is not necessarily complementary.
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Vincent Le Chevalier




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PostPosted: Mon 03 Apr, 2017 10:55 am    Post subject:         Reply with quote

I think that when a tool to measure swords is developed, it would be better to just abandon the waggle test and go for a pendulum test. I have cobbled together such a setup before, I just need to streamline the design in such a way that other can build their own. It would be safe enough to use on original swords.

The waggle test would then remain the gearless, accessible method it already is. People who are unsure of their accuracy, or need more precision, would use the pendulum test. The online tool could easily be adapted to treat measurements via a pendulum test too.

It is all in the pipeline Happy

Regards,

--
Vincent
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Fisher Lobdell




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PostPosted: Mon 03 Apr, 2017 11:22 pm    Post subject:         Reply with quote

I agree, the waggle test should stay the waggle test. It is accurate enough for pretty much everything, save reproduction. Wink
1 Peter 5:8 - Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:

Absence of evidence is not necessarily the evedence of
Absence. Ewart Oakeshotte.
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Simon McKenna




Location: Huddersfield, UK
Joined: 25 May 2016

Posts: 17

PostPosted: Tue 04 Apr, 2017 1:40 am    Post subject:         Reply with quote

I'd agree with Vincent's view that a pendulum test is the way to go for a reproducible, dare I say 'scientific' approach.

I have a relatively simple set-up that I've been using (see attached). The components (excluding tripod) only cost me about 15 and whilst I got the body machined by a colleague, the only important feature of the body is a straight bore of the right size to take the roller bearings.

This set-up seems to work reliably and the clamp copes well with a variety of sizes and can grip a bare tang without any difficulty. I'm still not sure whether it would be considered sympathetic enough to be used on an original museum piece though - others (Peter?) would have a much more informed view on this?



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Vincent Le Chevalier




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PostPosted: Tue 04 Apr, 2017 12:11 pm    Post subject:         Reply with quote

Given the surge of interest in the matter, I'm going to share my own pendulum setup sometimes next week. I just have to build it anew Happy

Here are the constraints that I've set for myself:
  • Low cost, low practical skill needed (if I can build one, anyone can Wink )
  • Low weight, portability
  • No calibration needed
  • Can adapt to any sword (or non-sword) shape, without putting too much stress on the object
  • Can measure oscillation period from several precise points (just as can be done for the waggle test)

The main problem I have with your device, Simon, as far as I understand it correctly, is that you will need to calibrate your measurements to take the inertia of the rotating part into account. Also, in what way do you measure with precision where the axis of rotation falls on the weapon?

I might be wrong, and we can certainly live with several alternatives for that setup anyway!

Regards,

--
Vincent
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Simon McKenna




Location: Huddersfield, UK
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PostPosted: Tue 04 Apr, 2017 12:54 pm    Post subject:         Reply with quote

Those are valid questions Vincent.

The inertia of the gripper is clearly small in proportion to that of the sword but I admit I haven't calculated it yet. As regards the axis of rotation, the design/dimensions of the gripper means that it can be made to fall on the central axis running down the length of the sword in most cases, which is what I wanted, but would work less well with different types of object. I've not yet quantified the measurement uncertainty associated with this issue.

You could add to the list the friction in the bearings that I'm using in the housing, and any error induced by the clamp/housing not being absolutely level - I use a spirit bubble to level the device but there's more uncertainty there.

I will have to put some values to these but I'd be surprised if they are significant compared to the uncertainty associated with measuring the period of oscillation and the simplified physics model being used to calculate moment of inertia, percussion length etc.

I'm currently exploring the potential use of reverse engineering/CAE methods to generate much more sophisticated results, but that as they say is another story and clearly not something that would be practical for widespread/general use.

Waiting with interest to see your set-up,

Cheers
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Alan Gideon




Location: Virginia
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PostPosted: Tue 04 Apr, 2017 1:38 pm    Post subject:         Reply with quote

Simon McKenna wrote:
I'd agree with Vincent's view that a pendulum test is the way to go for a reproducible, dare I say 'scientific' approach.

I have a relatively simple set-up that I've been using (see attached). The components (excluding tripod) only cost me about 15 and whilst I got the body machined by a colleague, the only important feature of the body is a straight bore of the right size to take the roller bearings.

This set-up seems to work reliably and the clamp copes well with a variety of sizes and can grip a bare tang without any difficulty. I'm still not sure whether it would be considered sympathetic enough to be used on an original museum piece though - others (Peter?) would have a much more informed view on this?


The YouTube channel Medieval Reviews presentation on this topic used a pair of high backed chairs as the pivot for the crossguard of an arming sword, with instructions on how to adapt another point near the grip if that location should prove troublesome for a given sword. It would be interesting to compare the repeatability of your jig to his.
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