Curved or Straight Blade?

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Curved or Straight Blade?

Postby Gordon H » 09 Oct 2012 21:33

I have had a few discussions with people over the weeks about this, I'm curious as to peoples perceptions of the straight sword blade and curved sword blade, in which areas do people think that one have advantage over the other and vice-versa.
I also wonder if anyone knows of any mention of this in historic sources as I'd be interested to read.
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Re: Curved or Straight Blade?

Postby admin » 09 Oct 2012 23:45

Curved blades cut better and straight blades thrust better. Simplistic I know, but after a couple of decades messing around with this question I think it basically covers it.
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Re: Curved or Straight Blade?

Postby Herbert » 10 Oct 2012 07:03

admin wrote:Curved blades cut better and straight blades thrust better.

I tend to disagree regarding the cutting. Test with similar cross sections, blade lengths, grip lengths and sharpness suggest that there is no real difference in cutting.
The thrusting is better with straight blades but decent enough with most curved ones. The end result will be much the same. The greater the curvature the bigger the chance of the blade turning when thrusting into a hard object (maille, shield etc.)

A greatly curved blade allows for a set of techniques that can't be done with a straight blade.

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Re: Curved or Straight Blade?

Postby admin » 10 Oct 2012 08:40

Herbert wrote:I tend to disagree regarding the cutting.


You're at liberty to, but a host of historical sources, including technical ones like Colonel Marey's treatise, plus general consensus, agree with me. :)
The fact is that given the same cross-section a curved blade hits, on average through a cut, the target at more of an angle, resulting in it effectively being 'sharper', because the angle of the gradient is in most cases halved. Think walking straight up a hill compared to walking at an angle up the same hill. Add to this vibrational effects on friction, which are a notable feature of straight blades but less and less so the more curved the blade gets. Add also that in pushing or drawing with the cut the curved blade has a far greater effect on the target because it accelerates the pressure (friction=slicing) exerted on the target.

Now, what many people confuse is impact energy on a target. Of course blade curvature makes no difference to that - if all you are doing is *hitting* a target then it makes no difference whether your blade is straight or curved (energy lost to vibration aside). However, cutting is entirely different, as you know, because the edge is entering the target and taking effect in different ways when passing through and out of the target.

Another advantage of curved blades in cutting is that they more easily cut *out* of the target - straight blades require a longer draw, or more angling of the wrist, to get free of the target after cutting into it.

EDIT TO ADD: Many people confuse curved and straight swords - the important part is the edge. A Type XVIII sword can in fact (and does by definition) have a curved edge. Most people would describe this as a straight sword, but the edge is in fact often as curved as some Japanese and Chinese swords, for example. Many European medieval swords are actually curved at their main cutting portions.
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Re: Curved or Straight Blade?

Postby admin » 10 Oct 2012 08:47

Check out the curve on the edge of Henry V's Type XVIII sword:

Image

Now a Japanese sword:

Image

Most cultures all over the world made their edges somewhat curved for a good reason.
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Re: Curved or Straight Blade?

Postby Andreas Engström » 10 Oct 2012 10:19

Putting cutting efficiencey aside for a while (though I do agree with Matt in that regard):

In sabre fencing I find that I can do some stuff more easily with a curved blade. Things like when you're bound in tierce, turn your wrist into seconde and thrust to the belly (a thrust that becomes quite difficult to parry). In essence you use the curve to "thrust around corners". You can do this to a lesser extent with a straight blade as well, but you don't get the "surprising" angle to the same degree.

Much easier to show than to explain in writing, I'm afraid. Basic concept is just "when in a bind, turn the back of the blade to the opponent's blade and use the interesting angle the curve gives you to thrust or slice him".

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Re: Curved or Straight Blade?

Postby Gordon H » 10 Oct 2012 12:56

I should have put this at the beginning of the thread, my apologies.
I am looking at wider technical aspect, not just cutting and thrusting.

1) Ease of forging: (Not speaking of modern techniques 20th-21st century)
2) Brittleness: eg: The Japanese Ken for example was straight and curved at the tip and double edged, though rumoured to be a very brittle blade and hence not very popular.
And most importantly:
3) Use in techniques: As Andreas previously mentioned.


In regards to straight and curved in regards to cutting and thrusting, how easy is to remove the blade from an opponents body in regards to cutting and thrusting with both types of blade.
As far as a curved blades in thrusting is concerned, i would of thought it easier to get under an opponents ribcage with a curved blade.
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Re: Curved or Straight Blade?

Postby Herbert » 10 Oct 2012 14:58

admin wrote:
Herbert wrote:I tend to disagree regarding the cutting.


You're at liberty to, but a host of historical sources, including technical ones like Colonel Marey's treatise, plus general consensus, agree with me. :)
The fact is that given the same cross-section a curved blade hits, on average through a cut, the target at more of an angle, resulting in it effectively being 'sharper', because the angle of the gradient is in most cases halved. Think walking straight up a hill compared to walking at an angle up the same hill.


This is one of the aspects I challenge - and so far no one has shown it conclusively to me (maybe I am a bad learner, maybe I am stubborn, but maybe…) Given the fact that one should make a cutting motion with both blades, the curvature is really just minimal regarding the point of contact, time spent in the medium and path travelled. My guess is that the curvature is not reducing the angle all that much.
Did you ever cut with a banana with a curved blade and one with a straight or almost straight blade? I could never feel a difference if the cross section, blade length, weight etc. were similar.
But also when you look at the angles involved, the difference is really negligible - or purely academic.

admin wrote:Add to this vibrational effects on friction, which are a notable feature of straight blades but less and less so the more curved the blade gets.

Now that is true and may make a noticeable difference. Thanks for pointing it out! This can of course be cancelled out by a good placement of the blade but who has such a perfect use, especially under difficult circumstances? Thanks!


admin wrote:Add to this vibrational effects on friction, which are a notable feature of straight blades but less and less so the more curved the blade gets. Add also that in pushing or drawing with the cut the curved blade has a far greater effect on the target because it accelerates the pressure (friction=slicing) exerted on the target.

Another advantage of curved blades in cutting is that they more easily cut *out* of the target - straight blades require a longer draw, or more angling of the wrist, to get free of the target after cutting into it.


You lost me here with these two. I don't get you. Care to elaborate?


admin wrote: Many people confuse curved and straight swords - the important part is the edge. A Type XVIII sword can in fact (and does by definition) have a curved edge. Most people would describe this as a straight sword, but the edge is in fact often as curved as some Japanese and Chinese swords, for example. Many European medieval swords are actually curved at their main cutting portions.

Good point - and you are right about that.


Gordon H wrote:As far as a curved blades in thrusting is concerned, i would of thought it easier to get under an opponents ribcage with a curved blade.


The ribcage is much less of a problem than people usually think. Ribs give and are slippery. To get stuck in a rib is quite unlikely, at least in my experience from working with dead pigs.

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Re: Curved or Straight Blade?

Postby admin » 10 Oct 2012 15:33

Herbert wrote:
admin wrote:Add to this vibrational effects on friction, which are a notable feature of straight blades but less and less so the more curved the blade gets. Add also that in pushing or drawing with the cut the curved blade has a far greater effect on the target because it accelerates the pressure (friction=slicing) exerted on the target.

Another advantage of curved blades in cutting is that they more easily cut *out* of the target - straight blades require a longer draw, or more angling of the wrist, to get free of the target after cutting into it.



1) When passing along or through a material that is being cut, the curved edge 'bites' in more than the straight edge, because of the curve. Hard to explain.. As an extreme example take a kukri or one of those wavy-bladed swords. Curved edges slice better than straight ones - this can be seen on kitchen knives.
2) Because a curved blade curves away from the target, it is easier to draw the blade out of the target once entered - the curve follows more closely the path of your cut (that path being essentially an arc). In other words, curves fit better into circles than straight lines.
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Re: Curved or Straight Blade?

Postby Mink » 10 Oct 2012 18:37

Herbert wrote:
admin wrote:The fact is that given the same cross-section a curved blade hits, on average through a cut, the target at more of an angle, resulting in it effectively being 'sharper', because the angle of the gradient is in most cases halved. Think walking straight up a hill compared to walking at an angle up the same hill.

when you look at the angles involved, the difference is really negligible - or purely academic.

I agree with Herbert on this one.
A curved blades provides two things that can help during cuts. One is an automatic slicing effect, even if you just swing around without any angle at the wrist, the blade will hit at an angle, which means the edge is effectively dragged across the surface. It is for the same reason that a guillotine blade is not a rectangle. See that "virtual guillotine" in this illustration, assuming the sword is rotating around the pommel:
Image
This slicing effect is especially significant on soft targets, and can be replicated with straight blades with a more complex cutting technique. It is the cumulative curvature that counts too, not the local one.

The second effect is that blade alignment is easier to get right, and more stable, because the center of gravity is actually in front of the point of contact during a cut. You can experience what I mean by just laying a curved blade on some horizontal object as if you were cutting it: if you relax the blade will naturally align with the edge vertical. A symmetrical blade does not do that. That makes the curved blade more forgiving, as edge alignment problems will correct themselves upon impact.

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Re: Curved or Straight Blade?

Postby Megalophias » 10 Oct 2012 18:55

A curved blade has less reach than a straight blade all else being equal. I'm not sure that makes much difference until you get into rapiers and such.
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Postby Ulrich von L...n » 10 Oct 2012 18:59

Andreas Engström wrote:... In sabre fencing I find that I can do some stuff more easily with a curved blade... "thrust around corners"... Basic concept is just "when in a bind, turn the back of the blade to the opponent's blade and use the interesting angle the curve gives you to thrust or slice him".

A couple of weeks ago I had an opportunity to do some light freeplay with an instructor of Ars Ensis: a rapier against a replica sabre (820 g, 80 cm blade, POB 16 cm, curvature 7-8 cm). After parrying and having a good bind it was quite easy to perform those surprise thrusts, and even cuts as described by Andreas.
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Postby Ulrich von L...n » 10 Oct 2012 19:06

Megalophias wrote:I'm not sure that makes much difference until you get into rapiers and such.

Interestingly enough in my case the rapier was 10-15 cm longer than my sabre. Naturally it would be foolish to draw serious conclusions based on one occasion, but nevertheless it was very surprising and interesting experience.
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Re: Curved or Straight Blade?

Postby admin » 10 Oct 2012 19:15

Megalophias wrote:A curved blade has less reach than a straight blade all else being equal.


Hmm, that's a bit like saying that 10kg of feathers is lighter than 10kg of rock. A 34 inch blade can reach a maximum of 34 inches, regardless of whether it is straight or curved (curved blades being measured in a straight line, not a curve).
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Re: Curved or Straight Blade?

Postby admin » 10 Oct 2012 19:20

Mink wrote:I agree with Herbert on this one.
A curved blades provides two things that can help during cuts. One is an automatic slicing effect, even if you just swing around without any angle at the wrist, the blade will hit at an angle, which means the edge is effectively dragged across the surface. It is for the same reason that a guillotine blade is not a rectangle. See that "virtual guillotine" in this illustration, assuming the sword is rotating around the pommel:
Image
This slicing effect is especially significant on soft targets, and can be replicated with straight blades with a more complex cutting technique. It is the cumulative curvature that counts too, not the local one.


Whilst you say you are agreeing with Herbert, everything you write above supports the fact that curved blades do in fact have an advantage in cutting, due to their curvature. Even your illustration shows it quite nicely! :D

The second effect is that blade alignment is easier to get right, and more stable, because the center of gravity is actually in front of the point of contact during a cut. You can experience what I mean by just laying a curved blade on some horizontal object as if you were cutting it: if you relax the blade will naturally align with the edge vertical. A symmetrical blade does not do that. That makes the curved blade more forgiving, as edge alignment problems will correct themselves upon impact.


Yes, this is another advantage of curved blades. I think of it like 'drag' on an aeroplane or suchlike. It's not the same, but it's similar in result. In contrary to this advantage, a disadvantage is that when you suddenly stop a curved blade, or change direction, the trailing 'tail' has a tendency to try and carry on going in the direction you were previously moving in, causing the sword to twist in your hand. Straight swords are IMO easier to stop and easier to change direction of attack with.
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Re: Curved or Straight Blade?

Postby Mink » 10 Oct 2012 20:30

admin wrote:Whilst you say you are agreeing with Herbert, everything you write above supports the fact that curved blades do in fact have an advantage in cutting, due to their curvature. Even your illustration shows it quite nicely! :D

Oh yes, I should have made it clear: I agree with him that the explanation with the edge angle (in cross-section) being diminished by the curvature is wrong :)

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Re: Curved or Straight Blade?

Postby Herbert » 10 Oct 2012 21:17

Usually the point of contact and the distance the blade travels in or through a target is so mall, that it hardly counts. The difference in within millimeters.

However - the differences in vibrations that Matt mentioned are worth a thought.

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Re: Curved or Straight Blade?

Postby Mink » 10 Oct 2012 21:33

About ease of manufacture, I've heard it said that it was easier to temper a curved blade than a straight blade, because there is a risk that the straight blade ends up slightly curved, whereas the curved blade just ends up marginally more or less curved. Makes sense I guess...

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Re: Curved or Straight Blade?

Postby Mink » 10 Oct 2012 21:37

Herbert wrote:However - the differences in vibrations that Matt mentioned are worth a thought.

I've always thought that the differences in vibration were due, in part, to the fact that a curved blade is ordinarily single edged with a back thicker than the middle of a straight double edged blade with the same edge angle. Has this been tested with swords of identical stiffness?

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Re: Curved or Straight Blade?

Postby Herbert » 11 Oct 2012 06:55

Mink wrote:
Herbert wrote:However - the differences in vibrations that Matt mentioned are worth a thought.

I've always thought that the differences in vibration were due, in part, to the fact that a curved blade is ordinarily single edged with a back thicker than the middle of a straight double edged blade with the same edge angle.

I think both are playing together. The fact that a curved blade has less vibration than a straight one AND that they usually are single edged. Although straight, single edged blades also vibrate - just not as much.

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