Cutting power- cutting ability in swords- a Primer..

[Harald Rotter]

Please forgive the profanity of my post ... a lot of technical terms are being thrown around, but arent we basically saying that curved blades are better at cutting than straight blades because they can be better drawn through the cut? And isn't this usually the first thing that is mentioned when talking about the differences between swords and sabres?

[Thomas Brogan]

It depends on your viewpoint and how you cut with your sword. If you are comparing a rapier to a sabre of similar width and cross-section, they will both cut roughly equally when cutting straight into the material. Should you perform a draw cut with each blade, the sabre will cut better than the rapier. Should you pierce the material with the point, the rapier should outperform the sabre.

Should you compare the sabre to a sword with a straight, but broader blade, the comparisons will change again.

Should you perform any cut with a misericord or a kris, the fabric of the universe will unfold.

That is my highly superficial understanding, at least.

[Tomehr Jochnowitz]

This may be off topic, but I believe that there are additional favorable properties to curved cutting blades. Namely, better energy retention due to better stress distribution.
Curved blades distribute energy from the point of impact more evenly than streight blades. The violent surge of vibration that reaches the ends of the streight blade are "lost" kinetic energy. Therefore, all things being equal, a curved blade will cut deeper.

[Robert Lyle]

I think it is a mistake to generalize without considering the target material.

A curved sword refuses the blade, so it appears (from the target's point of view) to widen more gradually, like the swept-wing on a jet. This reduces drag leads to excetionally deep cuts in solft materials.

But you need the wedge angle to cause failure in rigid materials. So hitting anything at least as solid as wood (including bone and metal) is best done at 90o, so a straight sword does just fine.

[Tomehr Jochnowitz]

Robert,

I agree that from the target point of view, the curved blade widens and wedges with penetration. However, I'm not sure this means less penetration, as the energy is more concentrated at the point of impact. I mean, an ax or spike will eventually wedge, but they will still penetrate further than a streight sword. The way I see it, a curved blade is somewhere in between.

[Robert Lyle]

Originally posted by Tomehr Jochnowitz
Robert,

I agree that from the target point of view, the curved blade widens and wedges with penetration. However, I'm not sure this means less penetration, as the energy is more concentrated at the point of impact. I mean, an ax or spike will eventually wedge, but they will still penetrate further than a streight sword. The way I see it, a curved blade is somewhere in between.

I said that the curved blade appeared to widen more slowly than a straight blade as it penetrates, from the targets point of view. This reduces drag and gives better penetration in soft materials, like flesh.

But rigid materials like wood, bone, or iron have a different failure mode and suffer more from a less acute entering angle, These targets suffer most from perpendicular collisions and straight edges are just fine. I don't see that an axe would be appreciably different from a sword of the same weight, although a spike concentrates the blow.

In short, a curved blade cuts deeply against a man with little armor, but metal, bone and perhaps cuir boulli will turn it. A straight bladed broadsword or light axe bites into bone, mail or light scale armor*, but is not impressive against soft tissue unless it breaks a bone. Against plate you need a heavy halberd or a hammer/poll axe with a spike. Common sense, really.

"into, not through necessarily.

[Angus Trim]

Originally posted by Robert Lyle
I said that the curved blade appeared to widen more slowly than a straight blade as it penetrates, from the targets point of view. This reduces drag and gives better penetration in soft materials, like flesh.

But rigid materials like wood, bone, or iron have a different failure mode and suffer more from a less acute entering angle, These targets suffer most from perpendicular collisions and straight edges are just fine. I don't see that an axe would be appreciably different from a sword of the same weight, although a spike concentrates the blow.

In short, a curved blade cuts deeply against a man with little armor, but metal, bone and perhaps cuir boulli will turn it. A straight bladed broadsword or light axe bites into bone, mail or light scale armor*, but is not impressive against soft tissue unless it breaks a bone. Against plate you need a heavy halberd or a hammer/poll axe with a spike. Common sense, really.

"into, not through necessarily.

You know, my cutting experience hasn't borne this out. My experience is that the straight double edged sword cuts soft targets as well as, if not better than the curved swords.

Its been my experience, that its not the curve of the profile that counts {actually seems to count for nothing}, but the edge geometry, the width of the blade, the angle of the main bevels, the rigidity of the blade, and the length of the blade........ {also mass, depending on what one can get to "terminal velocity"}

{terminal velocity meaning in this case, the highest speed one can swing a given sword}........

Thus the curve of the sword, in practice, isn't as important in cutting as other factors.......

A broad bladed type X can hold its own {at the very least} against a saber in cutting.....

A cutting biased 15th century longsword will hold its own, cutting, vs a katana........

Depending on various qualities, one or the other may cut the better, but its not the curve that will decide the issue {which cuts better}.........

[Tomehr Jochnowitz]

Thanks, Angus!

[KayaHan]

Originally posted by Angus Trim

..... Its been my experience, that its not the curve of the profile that counts {actually seems to count for nothing} .....

Mr. Trim, does this mean your cutting experience proved that curves on blades are useless? Is this your personal feeling, or do you have some objective results from repeatable, controlled experiments?

[Angus Trim]

Originally posted by Kayahan HOROZ
Mr. Trim, does this mean your cutting experience proved that curves on blades are useless?

No, doesn't mean useless at all, that's not what I said or implied. I mean its not the curve that makes for great cutting ability. Cutting ability as it applies to swords has more to do with edge geometry, blade geometry, weight, dynamic balance, etc...... as well as the subjective things like what the sword handler brings to the party......

There will be some folks that prefer a curved blade, in varying different degrees, and there are some sword arts that really use a curve, but that has more to with swordsmanship than a sword's raw ability to cut.

There is documentary evidence, for both straight and curved swords, cutting a man in half...... There is modern documentation for deer carcasses {and similar} being cut in half thru the ribcage with curved blades, and straight blades....... Which blade has the advantage then in cutting?

[KayaHan]

Please excuse my poor english; when I read the expression {actually seems to count for nothing}, I thought it refers to the curves on blades, which seems to count for nothing as per your experience..

And to answer your question, my humble opinion is, the sword which requires less effort to cut has the advantage, thinking that the arm holding this sword needs to perform the same cutting movement hundreds of times in a battlefield..

[Luke S Havily]

yes i agree. theres a large factore in sword construction, that it needs to be strong enough to cope with a human executing force on the sword, as it impacts a surface, it needs to hold strong an transfer the energy from the MAN.. ( "persons" ) weilding it, you find with samurie swords, katana, they are optimised for this, they can be used delacatly to make precise cuts, on precise serfaces with a very precise amount of force, for a verry precice, result... verry precise.
but ALLSO they can hold up to an event such as
"OH MY GOD WERE DID HE COME FROM!"
*swings wildly at foe*
an still hold strong, an transfer all the energy bult up from the swing and then ON the impact the continuing energy from the push, of forcing the blade threw somthing. wich is were the trick is, making it able to supas its own potential.

so therefor a raipier (havent actualy ever seen one :S) i supose, though light an to fast, if it was strengthand, somehow, you could exert more pressure on it, an therefore give it more energy to slice threw matter, AFTER the enitial impact an pearcing.

been doing sword play for about 4 years btw peeps, ^_^ no im not trying to brag, i havent actualy ever done any cutting, but i DO kno about the relation to an impact an the force that you put into it after the initial impact.

(just btw, anouther lesser known reason / effect, of the katanas flexable back, asweel as making it obsorb enegry from a hard impact, it ALLSO can work the outher way allwing you to actualy transfer your pushing energy into the impacted area, threw the sword, seemlessly, (i.e. as opose to, "laying" a sword on a target an THEN pushing down on it lol, bad example)

what im trying to say is that your bodys energy in pushing the sword After the swing, is completly conected to the swords own energy.
i dont kno if you guys understand what im saying. the enrgy from the swing, is its own enegry, it belong to the sword, then after you make the swing an the sword aproches the targed, with the katana you then put your waight behind it, an PUSH into the swing yourself, an becouse of the flexabilty of the spine it allwes your force to join up with the swords force. thats as plain an simple as i can put it..

what do you guys think.

[Tomehr Jochnowitz]

We are all imagining the same target, are we not? An armored or unarmored human. There is a reasonable compromise, around which we may debate; that is, the same type of test targets seem to appear regularly on SFI. Let us lay historical context aside, and appropriately judge all blades by the single standard of performance.
I suggest the following theoretical experiment (hopefully to be executed by a SFI member):
1) A free-hanging target (something that will take a while for people to begin arguing its validity, like animal carcass)
2) A scale
3) A ruler that measures degrees in a circle (sorry, don't know what it's called in English)
4) A velocity meter, like the kind used for measuring projectile speed of firearms (it would have to be the kind with two sensors, not three)
5) Test swords

A test sword is weighed. The target is weighed. A test cut is performed on the target with the sword, while measuring the wielding velocity, and the maximum angular deviation of the hanging target that results from the strike.
By calculating the kinetic energy of the wielded sword (using its velocity), and that of the target (using its angular deviation), we may discover the level of energy retention of the given test sword. The level of energy retention, along with the depth of penetration, will disclose the best sword.

[D. Opheim]

Originally posted by Luke S Havily
what do you guys think.

Hi Luke, I think you’re making things more complicated then they have to be. A sword cuts simply because it has and edge and is used on a target that is less dense. A good sword cut does not require a lot of force, just good handling and control of the cut itself. Transfer of force energy as you put it is not practical for a swords function. A blunt weapon like a club is a perfect example of what you’re saying, but not for a sword. The whole idea about cutting is to do it well and often if required without wasting a bunch of energy doing it. Edge geometry also plays a big roll, and there are plenty of topics that discuss this here on SFI.

[KayaHan]

Combining the information from Mr. Pearce’s and Mr. Lyle’s posts, can we assume that the curved sword is a result of the effort made to improve both the cutting ability and durability?

Beside the addition it makes to the sectional density, from the targets point of view, the curvature also provides a relatively more acute wedge angle at the POI than the edge that the blade actually has. This helps making a blade with a less acute edge (= improved durability) perform like a blade with a more acute edge (= improved cutting ability).

[Douglas S]

"Sectional density", that's as close a term as I can come up with as well. With a straight sword you can increase the Sectional Density (SD) by moving closer and offering a different angle of incidence (?) as well. IMHO, the curved sword lets you increase the SD without getting closer. No?

[C Henderson]

These principles also explain why broad headed axes have such awsesome cutting power, also the cutting angle of katanas could be applied to bearded halberds since the whole purpose of the beard is for over head strikes which usually hit at a 45 degree angle. anyways kudos on the disertation.

[Andy Vida]

Originally posted by Federico Fain
Michael,
I am not sure I understand why sectional density should increase if I cut at a 45 degree angle versus at a 90 degree angle (as you mention in the katana example).
This if sectional density can be summed up as the ratio of mass behind a unit of edge thickness at least, which is how I interpreted it.

One way of thinking about the effect of sectional density is to consider the force equation, F=ma. For any arbitrarily chosen cut to be made by a tool of a given geometry, a minimal amount of force will be required for successful execution. That force can be attained by either increasing the mass or the acceleration, or both. I can make two swords of identical physical geometry, one made of steel (sword 'S') and one of a magic metal called Unobtainium (sword 'O') which has 10% the mass of steel and all other characteristics including hardness, yield limits, etc. identical with steel.

Let us now assume that to successfully execute cut 'X' with either sword we must develop a force of 10 units. We can successfully execute X by using sword O at 10 units of acceleration or with sword S with 1 unit. Either way the force generated is 10 units, sufficient for the cut in question.

The practical reason why sectional density is important for swords is that humans are physically limited in terms of how much velocity they can impart to the blade in the execution of a cut. If we could make a 1 oz. blade that was as rigid and strong as its steel counterpart, the wielder would have to execute his cut with inhumanly high velocities in order to succeed. Since this is not readily possible, the swordsman uses a greater mass in order to be able to execute cuts at velocities that are not only humany attainable, but that allow him to maintain accuracy.

Another way to think about this is to think about a 1 pound force applied to two 1.4 inch metal rods against your skin. The first one is faced square on the end against your skin and the other sharpened to a very fine point. the 1 pound force on the first par will certainly be noticeable, but should not prove particularly problematic. The other rod, on the other hand, will probably be somewhat less welcome. Same force but differing areas of application will produce widely varying results.

Does this make sense?

-Andy

[Michael Tinker Pearce]

Good post Andy- very informative and correct but doesn't directly answer Federico's question.

The reason that the 45 degree cut increases sectional density is simple. The line directly across the width of blade is nearly half-again as short as the line crossing the width of the blade at a 45 degree angle. The longer line means more of the mass of the blade is directly behind the line of impact.

With regards to the Katana I have an illustration of this somewhere... Hmmm... can't find it- OK, here's a 'quicky' recreation- I took the line at 90 degrees, then the line at 45 degrees. I built a realistic cross section for a katan on the shorter 90 degree line, then copied and 'stretched' it to match the length of the line taken at 45 degrees. As you can see the length of the centerline has increased dramatically without increasing thickness. This will yeild a higher sectional density- a higher ration of length and width to mass. You will note that it also reduces the angle of the main bevels, IOW improves edge geometry.

[Andy Vida]

Originally posted by Michael Tinker Pearce
Good post Andy- very informative and correct but doesn't directly answer Federico's question.

The reason that the 45 degree cut increases sectional density is simple. The line directly across the width of blade is nearly half-again as short as the line crossing the width of the blade at a 45 degree angle. The longer line means more of the mass of the blade is directly behind the line of impact.

There is another dimension to this: slicing, which can be made to take advantage of sectional density properties to increase cutting ability.

Slicing relies on two principles, that of the wedge and usually to a lesser degree, that of sawing due to microscopic serrations at the cutting edge. The action of these serrations renders the sword as an impulse weapon like a club. The difference is the area to which the impulse is focused. Because that area is so small, we call the net effect a "cut" rather than blunt trauma, but the physics of the action are principally identical. All kenujustsuka on the edge of passing out should start breathing into a paper bag immediately.

Before you poo poo this, consider the effects of a snapped arrestor cable on an aircraft carrier. I've seen the results of this action and the two halves of the body are cleaved every bit as tidily as would be the case with a katana. The results are largely a matter of the precise manner in which force is applied.

Take, for example, a wood plane. If I align the plane such that the cutting edge is square with the line along which the cut is made (e.g. going straight across the edge of a board), cutting will require more effort on the part of the hands doing the pushing or pulling of the tool than if they were to cant the edge at, say, 45* to the line of the cut. The wedging action will actually impart greater ease and control to the wielding hands. Add to this the saw-like action of the micro serrations at the edge and the cutting becomes much more powerful.

The precise same principles are made use of in a Globe meat slicer that you find at your local deli, only those rely more on the micro-serrations. Were the blade not in rotation, making a neat cut would prove a problem, but the addition of a gentle angular motion allows the blade to slice through cold cuts (and body parts) with almost imperceptible ease.

A hydraulic paper cutter takes advantage of serrations. The blade makes contact with the stack of paper parallel to its upper surface, but as the blade is pushed downward there is also a lateral motion, the cut being about 45* as I recall.

In another world, a squaring shear (used to cut long runs of steel sheet and plate) usually has the blade canted at about 1/2* to the surface of the material so that the cut starts at one end and travels toward the other end, effectively increasing the sectional density of the cutter by applying force to a smaller area, rather than attempting to bully the blade through the entire breadth of the material.

The same may be said for the katana. And angular, drawing cut will have more power than a simpler chopping motion. This is one of the main reasons the Japanese adopted the incorporation of sorii in their blades, the original being increased ease and safety of the draw. Sorii made the blade easier to draw without mangling one's own hand in the process. The added bonus they discovered was that a curved blade demonstrated notably superior cutting mechanics. This pretty well spelled the end of the <mumbledypeg> straight swords. Damn my memory...

It should be noted that using wedging principles increases the power of an implement but decreases efficiency somewhat. There are no free lunches. For example, lets say we wish to make a hole in a piece of steel plate and all we have is a tool steel bar and a lathe abd the plate has a small hole in it already. We can approach the opening of that hole in one of two ways. We could attempt to drive the squared-off end of the bar straight through the plate in the manner of a punch press or we could "drift" the hole by tapering the rod using the lathe. Since we do not have a punch press we will not be able to avail ourselves of the first option. We therefore turn a very slight taper on the rod and hammer (yes, we DO have a hammer, too) the bar trhough the small hole, widening it as we proceed.

This is a somewhat silly example, but it illustrates the principle of the wedge and just how powerful mechanical advantage can be. Ancient people such as the eqyptians quarried huge stone blocks using notihng more than feathers and wedges driven into cracks or holes in the stone.

Anyway, it all about leverage and taking the best advantage of it.

-Andy

[Michael Tinker Pearce]

Is 'Chokuto' the word you are looking for?

All sword cuts draw to some degree due to the arc of the cut and microserratons are present in all sharpened steel edges. Some more micro than others...

Curved blades do increase the drawing effect by presenting the edge at an angle, but comparing them directly to straight swords is tricky. In actual practice katanas don't necessarily cut better than Euro-swords designed for cutting. I prefer not to compare- both work and a good sword is a good sword.

[Michael Mason]

Mr. Pierce and Co.,
This is really a question for smarter heads than mine, more than a statement of any kind of scientific principle.
(sorry, I realize it's been awhile since this thread was active)

Rather than use words, I have attached a small diagram which (I hope) summarizes my primitive understanding of curved edges vs. straight ones...
(VAST OVERSIMPLIFICATION WARNING AHEAD)
The short version rests on the idea of "contact area size" vs. sectional density.

(All images uber-simplified to illustrate point...)

#1 - Curved edge : Small contact area
#2 - Straight edge at 90 degrees : LARGE contact area
#3 - Straight edge at angle NOT 90 degrees : SMALL contact area

My crude understanding would be that smaller contact area size would increase effective sectional density for cutting purposes, notwithstanding ALL the other factors which affect this. Is this correct?

Really, what I think I'm saying is that curved blades offer a mechanical advantage, but that mechanical advantage can be offset (perhaps completely) by a very slight angle adjustment with the straight blade. Am I even close?

1) Does the "draw" cut return some of this advantage to the curved blade
2) if so, is this due to "contact area" issues, or is it something else (micro-serrations, edge geometry, or most likely, a combo of 19 different things)?

Luckily, thanks to the efforts of folks like Mr. Pierce and Mr. Trim (and thousands of others, throughout history), I don't really need to worry about this stuff. I can focus on safety & technique. The sword will do it's job if I do mine.
Thanks to all the smiths out there.

[D. Opheim]

This is really a question for smarter heads than mine, more than a statement of any kind of scientific principle.

To simplify there are several factors in the art of cutting.

Edge; blade geometry; and type (or angle) of contact on the cutting medium.

First, all blades with an edge will "cut", so the question is how to do it best.

Every blade will have micro serrations along the length of the edge and when enough pressure is applied and drawn across the medium, it will "cut", plain and simple.

In your diagrams, #3 is the most common angle for cutting with sword blades, the exaggerated #1 for say a curved blade will still yield the same results; #2 is more of a chopping angle like and Axe. It can still cut, but is less likely to go through the whole cutting medium.

I hope that clears some things up, but this subject will have multiple answers.

[Andy Vida]

Is 'Chokuto' the word you are looking for?

Yeah. My memory seizes up sometimes.

[Al Massey]

You have to also take into account what angle the blade strikes at. Many straight cutting swords I've seen had a grip which in effect prevented the wrist from fully pronating in a strike, thus insuring the blade edge would strike the target at an optimum angle for penetration. Think in terms of cutting a tomato with a non-serrated knife, the difference between bringing a blade straight down or cutting at an angle.