Ideal Sword Design

[Liam Ryan]

I like the second one, but with a thicker blade like the top one.
Also a big fan of the gladius and the rob roy sword

 

[Wolf_1989]

Purely food for thought. My expectation is that none of us will likely use or face a sword in real combat.

Certainly. This is 2008 AD.

I'd only use a blade if my .45 was empty.

:thumbup:

 

[Watchful]

Although, defensively...there are a number of sword attacks occurring in the US, Canada, and Europe each year!

But offensively, or sword against sword... not me. Or anyone else I know.

 

[the possum]

For further clarification, the cop or harmonic nodes or whatever you want to call them are a different thing than the pivot points. (even though they may happen to coincide on a given sword) If we're talking about painful shock to the hand, then that's a function of the pivot points (poorly placed). "Vibrations" or sine wave like motion are associated with the harmonic nodes.

 

[Bors]

For further clarification, the cop or harmonic nodes or whatever you want to call them are a different thing than the pivot points. (even though they may happen to coincide on a given sword) If we're talking about painful shock to the hand, then that's a function of the pivot points (poorly placed). "Vibrations" or sine wave like motion are associated with the harmonic nodes.

That painful shock that’s felt in say baseball bats and crowbars for example are the result of harmonics. Simply it's high frequency high amplitude standing waves in the object. Because both are short and very stiff low frequency vibrations are suppressed in favor of high frequency vibrations. That’s why it feels like being shocked when it happens.

All objects when excited sympathetically or by force will vibrate at a natural frequency or set of natural frequencies the lowest of which is the fundamental frequency. These frequencies are associated with a standing wave pattern. Standing waves are described as reflected waves from one end of the medium that interferes with the incident wave and establishes specific points (nodes) along the medium that have the appearance of standing still. These patterns are only created at specific frequencies and are known as “Harmonic Frequencies” or simply harmonics. Frequencies other than these result in irregular non-repeating wave patterns.

Holding a sword vertical and striking the pommel or handle, we establish a harmonic pattern in the blade. Within the pattern we see two interference points or “Nodes” one is located in the upper third portion of the blade the other is located near the guard. The one in the upper third is often call the “sweet spot” or more commonly the center of percussion (COP).

To completely suppress harmonics is impossible however, careful thought to design can control or more specifically dampen the effects. Many factors influence how swords vibrate and what frequencies are favored such as shape, mass distribution, fuller design, heat-treating. How well a sword handles, how well it reacts during and after impact are influenced greatly by harmonics and how well they are dampened.

 

[Watchful]

Bors-- incredible post! I've got to copy that one as an excellent reference. Nice work, sir.

 

[the possum]

I disagree. If the COP and pivot points do not coincide, you can still get tremendous hand shock even if you strike at the COP. This is because the impact will naturally want to make the sword/bat/bar rotate. If it rotates around a point within your grip, the handle does not change speed/direction suddenly, so you don't feel the shock. If this point gets very far from the grip, the handle will want to change motion violently upon impact- leading to loose guards, broken tangs, and hand shock. This was one of the main problems with the khukri I modified. I fixed the hand shock issue by moving the mass around to effect the pivot points. I.E., the behavior was perfectly explaned by the pivot point principles, and I used them predictably to modify the blade to what I desired.

 

[Bors]

I disagree. If the COP and pivot points do not coincide, you can still get tremendous hand shock even if you strike at the COP. This is because the impact will naturally want to make the sword/bat/bar rotate. If it rotates around a point within your grip, the handle does not change speed/direction suddenly, so you don't feel the shock. If this point gets very far from the grip, the handle will want to change motion violently upon impact- leading to loose guards, broken tangs, and hand shock. This was one of the main problems with the khukri I modified. I fixed the hand shock issue by moving the mass around to effect the pivot points. I.E., the behavior was perfectly explaned by the pivot point principles, and I used them predictably to modify the blade to what I desired.

The COP is a quite zone where both waves the incident and the reflected are canceled. The shock is the result of a high amplitude high frequency wave generated from a high force point of impact either above or below the COP that stimulates one of the “higher” harmonic frequencies. This wave travels parallel to the axis of the blade.

Striking the exact point but with less force will also stimulate the higher harmonic frequency however, because less force was used the amplitude of the wave will be less.

Striking at a point other than ones that stimulate harmonic frequencies will generate random vibrations which are not to be confused with “harmonic frequencies”.

Some of the things that can help manage the harmonics are handle material, blade shape, fullers and mass distribution. Handle material and how it’s fitted can greatly reduce how much of the vibration is transferred from the source in this case the blade to the hand.

The main issue in swords are low frequency harmonics because they tend to be thin wide and long. With short knives like Bowies and khukri’s the the harmonics are at much higher frequencies. A tight fitting shock absorbing handle will dramatically reduce shock on short knives..

There is a second force generated as well. This is a leverage force. Using a straight steel bar say 3' long strike a hard round object directly on the COP. All the energy is transmitted to the target with no shock and no vibration like a dead blow hammer. Now we strike the same hard object again but this time we strike it halfway between the guard and the COP. This time you will feel a jolt to the hand and a upward force perpendicular to the axis. This is a result of leverage pivoting force and not Harmonics. If we strike again this time with just the point the force will be downward perpendicular to the axis. The bar will try to jump out of you hand.


Both of these forces can act at the same time during impact. You can have a “high frequency” harmonic wave traveling parallel to the axis and a leverage rotational force generated perpendicular to the axis.

I once had a Viking sword climb out of my hand do to the leverage rotational force during cutting when I inadvertently struck the 2x4 target base.
It can be quite a surprise LOL. Fortunately no one was hurt and the sword was fine.

 

[the possum]

Some of the things that can help manage the harmonics are handle material, blade shape, fullers and mass distribution. Handle material and how it’s fitted can greatly reduce how much of the vibration is transferred from the source in this case the blade to the hand.

From what I gather of the makers who like to play with this concept (Gus & Tinker mostly), they far prefer to manage them with blade properties so they don't have to worry about shock absorbing handle materials.

With short knives like Bowies and khukri’s the the harmonics are at much higher frequencies. A tight fitting shock absorbing handle will dramatically reduce shock on short knives..

Again, I don't like referring to issues with vibrations as "shock", since they don't seem nearly as important in that regard as the lever/rotational force. If I had just rehandled my khukri with rubber or something, maybe it wouldn't have numbed my fingers any more, but it still wouldn't have solved the root of the problem.

There is a second force generated as well. This is a leverage force. Using a straight steel bar say 3' long strike a hard round object directly on the COP. All the energy is transmitted to the target with no shock and no vibration like a dead blow hammer.

Again, this is assuming the COP and pivot points line up. Also, the ideal location to strike with depends on the swing and target resistance. The sword transfers max energy to the targe with a blow that stops both the linear and rotational motion. I.E., stops it cold. This may be at the COP for some targets, and elsewhere for others.

Now we strike the same hard object again but this time we strike it halfway between the guard and the COP. This time you will feel a jolt to the hand and a upward force perpendicular to the axis. This is a result of leverage pivoting force and not Harmonics. If we strike again this time with just the point the force will be downward perpendicular to the axis. The bar will try to jump out of you hand.

Yes, this is what I was mainly talking about. Let me rephrase your example another way. Take that straight rigid steel bar, and put a bearing somewhere in the middle, and attach it thus to a firm base so it can pivot up and down just like a teeter-totter. You hold one end level with your hand, while I whack the other end with a big hammer. Now, is the "shock" you feel in your hand mostly due to vibrations traveling in a sine wave through the bar, or simply from the fact that the bar is pivoting upward into your hand with the force of a hammer blow?

 

[Watchful]

Damn fine thread, and thanks to Bors and The Possum for making it so.

I have a question, though, and hope either of them can answer it.

Now, is the "shock" you feel in your hand mostly due to vibrations traveling in a sine wave through the bar, or simply from the fact that the bar is pivoting upward into your hand with the force of a hammer blow?

Wouldn't it be both? The vibrations represent the energy of the blow, but the force is transferred via the fulcrum.

One is the manifestation of the kinetic energy, but the other is the mechanism of the force.

Or, to put it in a simpler analogy, if I close a door, the mechanism of the force is the door swinging on its hinges, whereas the creak of the hinges is the manifestation of the energy. Both are related to the same event, and neither excludes.

The Possum raises a fascinating idea, though, on how the effects of COP differ on blades like a kukhuri or a falcatta, where you don't have a straight edge.

I liken this to the sometimes intriguing aspects of a full axe, where the center of percussion requires that the axe handle be curved with belly to make that sweet spot exist where the hands are held... otherwise, the node would be a few inches off the back of the knob!

 

[Bors]

From what I gather of the makers who like to play with this concept (Gus & Tinker mostly), they far prefer to manage them with blade properties so they don't have to worry about shock absorbing handle materials.

Over the many melania wood has been favored for its ease to work with and it’s ability to act as an insulator. These properties haven’t changed. Gus and tinker blades tend to be on the thin side which makes them just a little more lively in the hand. If the impact is correct on soft targets they cut very well however, the blades can resonate quite a bit if the blade (some of them) is off axis at impact. This can be good and bad depending on how you look at it. Some swords will break or take a set under these conditions however, Atrim’s swords tend to be very forgiving which makes them very good swords for beginner and advanced alike.

Again, I don't like referring to issues with vibrations as "shock", since they don't seem nearly as important in that regard as the lever/rotational force.

I see you point here but In many cases the high amplitude vibrations are compared to an electrical shock in feeling. That's why I used the word shock in this case. The importance of harmonics both high and low are very important.

Low frequency harmonics can make it hard to recover the sword after impact, especially in a glancing blow on a hard target. This generally is a characteristic soft heat treating although not always however, mass distribution, fuller design and placement also contribute.

High frequency harmonics have a different effect. If the handle is poor the sword can be dropped from the vibration/shock transmitted to the hand. They can crack handles and I suppose under the rite conditions the blade could crack or break much like a crystal glass.

Harmonics can only be dampened and how well this is done depends on materials, design, heat treating protocol and the makers level of understanding.

Again, this is assuming the COP and pivot points line up. Also, the ideal location to strike with depends on the swing and target resistance. The sword transfers max energy to the targe with a blow that stops both the linear and rotational motion. I.E., stops it cold. This may be at the COP for some targets, and elsewhere for others.

The COP and pivot point/lever point will “always” line up together at the COP. When struck exactly there are no rotational forces and no harmonics exerted in or on the bar/sword at the COP.

It’s when the impact is to either side that these two forces split up and begin to react.
For example striking half way between the COP and gripping point may not stimulate a harmonic frequency but may generate random vibration which is much less in amplitude and how it is “felt” in the hand, however this can set into motion strong rotational forces which can “Shock/Jolt” the hand.

Impact at the COP causes the least reaction in the sword and transfers the most energy to the target so it’s always the optimum place to strike. But you can’t always strike there an example would be cutting a thick target. Starting the cut at the COP may mean that you only cut halfway through the target so in this case the point of impact will have to be moved closer to the handle to allow enough blade length to completely cut through the target.

This will in turn set into motion rotational forces. Depending on sword design and sharpness In a soft target like mats you may not notice much at all. With a hard target the shock/jolt to the hand will be more. Vibrations (harmonics) won’t be stimulated as long as the blade impacts on axis and remains on axis through the target.

Yes, this is what I was mainly talking about. Let me rephrase your example another way. Take that straight rigid steel bar, and put a bearing somewhere in the middle, and attach it thus to a firm base so it can pivot up and down just like a teeter-totter. You hold one end level with your hand, while I whack the other end with a big hammer. Now, is the "shock" you feel in your hand mostly due to vibrations traveling in a sine wave through the bar, or simply from the fact that the bar is pivoting upward into your hand with the force of a hammer blow?

What you have described is a basic lever and you are quite rite that is “Shock” however shock is one of those multi meaning words. It can be used to describe blunt force as generated by lever rotational forces or it can be used in an electrical sense which is the sensation you get from High frequency harmonics.



Good discussion by the way :thumbup:

 

[Bors]

Damn fine thread, and thanks to Bors and The Possum for making it so.

I have a question, though, and hope either of them can answer it.
Quote:
Originally Posted by the possum View Post
Now, is the "shock" you feel in your hand mostly due to vibrations traveling in a sine wave through the bar, or simply from the fact that the bar is pivoting upward into your hand with the force of a hammer blow?
Wouldn't it be both? The vibrations represent the energy of the blow, but the force is transferred via the fulcrum.

Possum is referring to rotational (fulcrum) forces and not the sine (harmonics) vibrations.
The fulcrum rotational force will transmit a shock/jolt to the hand in the form of blunt force. The sine (harmonics) wave will also transmit a shock but it will have the “feeling” of an electrical shock. I know it can be confusing......

One is the manifestation of the kinetic energy, but the other is the mechanism of the force.

Or, to put it in a simpler analogy, if I close a door, the mechanism of the force is the door swinging on its hinges, whereas the creak of the hinges is the manifestation of the energy. Both are related to the same event, and neither excludes.

Both can effect felt vibration (amplitude) and fulcrum rotational force. But you can have one without the other.

High frequency harmonics may only become an issue while striking a hard target and then only if the strike is above or below the COP. Low frequency harmonics will be an issue if the strike is off axis regardless of where the impact is.

The Possum raises a fascinating idea, though, on how the effects of COP differ on blades like a kukhuri or a falcatta, where you don't have a straight edge.



I liken this to the sometimes intriguing aspects of a full axe, where the center of percussion requires that the axe handle be curved with belly to make that sweet spot exist where the hands are held... otherwise, the node would be a few inches off the back of the knob!

Yes he does, putting a curve/bend in something does change things. For example a curve can have a dampening effect on low frequency harmonics.

Reply With Quote

 

[the possum]

Now that I see we were just using the terminology in different ways, I can agree with much of what you're saying, except this one part stands out to me:

The COP and pivot point/lever point will “always” line up together at the COP. When struck exactly there are no rotational forces and no harmonics exerted in or on the bar/sword at the COP.

It’s when the impact is to either side that these two forces split up and begin to react.

So, how are you defining COP and the pivot/lever points? When those guys are discussing harmonic nodes as they relate to the COP, they are talking about a harmonically "dead zone" (node) hopefully somewhere in the handle right behind the guard, and another corresponding one out on the blade roughly 1/3 of the way back from the tip. But there are infinite pairs of pivot points all along the blade and handle, or even out into space beyond. If one pivot point is right behind the guard, the corresponding blade one may be at the COP, (Gus has said he does this intentionally on some (many?) models) or it may be well behind it, or it may be several feet out beyond the tip of the blade, depending on the mass distribution throughout the piece.

The center of mass/gravity should be the only location where an impact will not cause the sword/bar to rotate. Anywhere on either side of the CoM (not COP) will cause rotations.

 

[the possum]

Damn fine thread, and thanks to Bors and The Possum for making it so.

I wouldn't have bothered responding to a thread titled "Ideal Sword Design" if AfterTFD hadn't brought up some good points that interest me. And now I notice Mr. Camerer is lurking- hope he can add something as well.

 

[Bors]

Now that I see we were just using the terminology in different ways, I can agree with much of what you're saying, except this one part stands out to me:

We’re on the same page.

Originally Posted by Bors View Post
The COP and pivot point/lever point will “always” line up together at the COP. When struck exactly there are no rotational forces and no harmonics exerted in or on the bar/sword at the COP.It’s when the impact is to either side that these two forces split up and begin to react.

So, how are you defining COP and the pivot/lever points?

COP:
This is a fixed point about 1/3 of the way down from the point. This point can vary a little based on blade geometry but is always a fixed point.

COG:
Center of gravity/mass. This position varies based on mass distribution.

Rotational point or Fulcrum rotational point:
Any point of impact along the object (bar/sword) the value is infinate.

When those guys are discussing harmonic nodes as they relate to the COP, they are talking about a harmonically "dead zone" (node) hopefully somewhere in the handle right behind the guard, and another corresponding one out on the blade roughly 1/3 of the way back from the tip. But there are infinite pairs of pivot points all along the blade and handle, or even out into space beyond. If one pivot point is right behind the guard, the corresponding blade one may be at the COP, (Gus has said he does this intentionally on some (many?) models) or it may be well behind it, or it may be several feet out beyond the tip of the blade, depending on the mass distribution throughout the piece.

The center of mass/gravity should be the only location where an impact will not cause the sword/bar to rotate. Anywhere on either side of the CoM (not COP) will cause rotations.

The fundamental harmonic frequency is the lowest frequency that the blade favors. Hold the blade vertical and strike the pommel. The resulting sine wave (harmonic) is the fundamental one.
This one is the important one. It shows you where the two nodes are. The first node is the COP the second node is at 180 degrees or usually somewhere around the guard this is just a quite zone and pertains to harmonics. The first and second nodes are always 180 degrees apart at the fundamental frequency.

I’m not exactly sure what Gus is talking about. If they are calling the node (quite zone) at the guard a pivot point then the COP has to be 180 degrees or ½ of the wave in front of it.

I’m not at all sure what Gus’s definition of “pivot point is”. I don’t think it the same as what we are talking about.

The center of mass/gravity should be the only location where an impact will not cause the sword/bar to rotate. Anywhere on either side of the CoM (not COP) will cause rotations.

What you say would be true if the sword was not traveling in an arc however, when you swing a sword it’s in an arc the radius of which is centered at the elbow (for the sake of this discussion) and extends to the point of the sword.

The moment the sword makes contact that point becomes a fulcrum. Striking the sword at the COG while traveling in an arc the momentum will want to carry the sword forward, that is the point pivoting forward. This sets up a rotational force into the hand that will be a jolt/shock.

If you strike the sword at the COP there will be no jolt/shock and no harmonics because the quite zone imparts no rotational or harmonic actions.

 

[Bors]

Ok so I did a little poking around at SFI and found a pic that tinker put up.
There is a typo he uses COG (center of Gravity) to describe COP (center of percussion).
Take note of the placement of the node at the handle.

I agree that this is "Balancing" that is getting the placement of the nodes correct, also I add dampening the wave amplitude as part of the "balancing"



It depict's the Fundemental Frequency rather well.

Very good picture

 

[Bors]

Here is a second one on "complex" harmonics. It depics the effects of a heavy pommel.

 

[the possum]

You can get some more of Tinker's thoughts on that subject much more recent than those illustrations, in this thread about harmonic nodes. There is some more interesting info on that subject scattered through the later pages of this thread.

You've probably already seen the article on the ARMA site, but others reading may be interested. sword impacts & motions
I still think this is the place to start for understanding the pivot points.

There's a great spotlight thread over on MyArmory discussing all this stuff.
Balance points, pivot points, and nodes on the sword

 

[the possum]

Ah! Finally found the other thread I was looking for-

Simulation of blade properties

In many cases in these threads guys are making the assumption that the pivot point associated with the crossguard (or just behind- Cliff called this the "dynamic balance point") is at the same location as the harmonic node or COP. I gather this makes things much easier for calculations and such, but this is by no means absolute. The COP must always (obviously) be on the blade. The forward pivot point corresponding to the cross may well be off the end of the blade. I have such a sword.

 

[Fenris131]

I myself prefer my Seax. 28'' overall. perfect short combat sword, although....i must say... I truly do desire a Templar Longsword. Always been a fan