Yojimbo 2 wharncliffe with straight edge vs. curved sword cutting philosophy

[chiselman]

From countless cutting tests and discussions over the years, it's generally believed that the wharncliffe style blade in the Yojimbo 2 (Yo2) maximizes cutting ability for the blade length because force is imparted to the target all the way to the tip of the knife. In a knife with a curved blade, the curved tip of the blade may tend to slip off of the target.

Yet, it is also accepted that curved swords generally cut better than straight swords. There are lots of reasons for this:

- Adding curvature to the blade provides a way to add mass towards the end of the sword without overly thickening blade stock. As the center-of-balance moves away from where the hand, chopping ability improves. The Yo2 adds mass to the blade by having a thick blade stock (tapering to reasonably thin at the edge) and being tall, which helps with chopping power.

- Curvature places the center-of-balance behind the swing which improves edge alignment due to momentum. Having a tall and stiff blade also certainly improves edge alignment in the Yo2 when cutting into a target.

- A curved blade naturally follows the arc of the arm as well as the wrist, which allows for a slicing path that follows natural bio mechanics when a person swings their arm. At least in a sword, having some of the force directed away from the target is actually desirable to cause "intentional" slipping. This is because a slice is much more effective than a chop at cutting. For example, if you want to cut a steak, it's much easier to cut if you draw the blade across the meat applying a shearing force vs. pushing straight down on the steak with the blade and applying a compression force.

I accept that the wharncliffe blade in the Yo2 is superior for cutting. BUT, I also accept that a curved blade profile in a sword is superior for cutting.

How do we reconcile the two? Does a difference in size change the fundamental physics of cutting? Since the hand moves in an arc around the wrist, isn't the wrist like a "mini-arm" where a curved blade aligns with the bio mechanical movement of slicing? In the Yo2 superior in certain cuts such as the comma cut, chop cuts, and tip cuts, but less effective at full arm swing slicing?

[chiselman]

bump

[Ez556]

I’m no expert by any means, but I think the key does lie in the blade length. The benefit the Wharncliffe blade gives really shines when you are looking at shorter blades that otherwise wouldn’t have the cutting power behind it. Box cutters are extremely effective at cutting. Knives like the Squarehead which is basically a box cutter in terms of edge shape and size are great cause all the power put into that short blade is focused at the tip. As you go up the chain though, I think the benefit starts to decline. Dragonfly, Delica up to the Yojimbo still can benefit from the shape due to their relatively small size but to me, at the point you get to the Yojimbo you start to have a loss of return. If you are talking slash cuts with a larger blade like a Endura, how much of the blade are you really using? As you stated, slicing is much more effective than chopping, and once the blade travels deeper into whatever material is being cut and the arc puts the knife more perpendicular to the material being cut, you start to get more into the realm of chopping rather than slicing, whereas the first 2-3 inches of blade benefitted from the extra slicing power. Now look at that same Endura length blade with a curve to it, and as the blade travels deeper into the material being cut, the curve allows the blade to keep its slicing motion throughout the arc rather than becoming perpendicular to the material at the same depth. I’m a huge fan of the Wharncliffe blade but to me, anything larger than say a Delica with a Wharncliffe blade kind of loses the benefit unless you are just looking for extra reach alone. Dragonfly Wharncliffe good. Military Wharncliffe bad.

[Evil D]

Well, one is 3.5 inches and the other 3.5 feet. I'd also add that swords like the katana are highly romanticized and there are plenty of straight edged swords that can hack a man in half with ease. Nova/PBS did a special on a Viking sword and there was an interesting bit in the beginning talking about the katana vs a broadsword and the guy demonstrated that a blunt broadsword would still slice through rolled up straw mat just the same as a katana.

Anyway knives are just a different world. Look up some of the pork man cutting tests.

[Ez556]

The Viking Seax is a kick butt looking blade.

[sal]

Hi Chiselman,

Welcome to our forum.

This is an interesting subject and worthy of discussion. I'm snowed right now, but will share my thoughts later this weekend. The short story, in my opinion, is the function and physical motions used in cutting.

sal

[Wartstein]

....
Yet, it is also accepted that curved swords generally cut better than straight swords. There are lots of reasons for this:
....

One more point/theory why curved swords cut better than straight ones:

Due to the curvature, a bit less edge comes in contact with the target (the more curved, the less edge).
Consequently the force is concentrated on a smaller amount of edge, which will penetrate better due to that.

No idea if that's true (might be NOT, since it's the slicing motion that counts for a good cut, but just by physics the theory is quite logical). Just read that in articles about sword fighting and HEMA (historical european martial art). I never actually practiced that, but for example lonerider does, maybe he'll chime in...

[chiselman]

....
Yet, it is also accepted that curved swords generally cut better than straight swords. There are lots of reasons for this:
....

One more point/theory why curved swords cut better than straight ones:

Due to the curvature, a bit less edge comes in contact with the target (the more curved, the less edge).
Consequently the force is concentrated on a smaller amount of edge, which will penetrate better due to that.

No idea if that's true (might be NOT, since it's the slicing motion that counts for a good cut, but just by physics the theory is quite logical). Just read that in articles about sword fighting and HEMA (historical european martial art). I never actually practiced that, but for example lonerider does, maybe he'll chime in...

Right, in theory it makes sense - the curvature causes force to be imparted to a smaller surface area, at least on initial contact and prior to any push / draw cuts.

I too am not certain about how that theory translates into practice. On one hand, the human body is round and soft, so flesh would compress and possibly make the difference minimal for the amount of edge in contact with the target. On the other hand, I've read HEMA accounts that a cut to the arm may cause more injury than a cut to the stomach area due to more force being distributed with a sword impacting the stomach area. I am not a HEMA or sword fighting expert, so this is all conjecture.

I suppose for knives, the practical way we cause less edge to come in contact with the target is by decreasing the edge angle or making the blade thinner behind the edge.

[chiselman]

Hi Chiselman,

Welcome to our forum.

This is an interesting subject and worthy of discussion. I'm snowed right now, but will share my thoughts later this weekend. The short story, in my opinion, is the function and physical motions used in cutting.

sal

Thanks for the welcome Sal! I'm looking forward to your thoughts.

[chiselman]

Well, one is 3.5 inches and the other 3.5 feet. I'd also add that swords like the katana are highly romanticized and there are plenty of straight edged swords that can hack a man in half with ease. Nova/PBS did a special on a Viking sword and there was an interesting bit in the beginning talking about the katana vs a broadsword and the guy demonstrated that a blunt broadsword would still slice through rolled up straw mat just the same as a katana.

Anyway knives are just a different world. Look up some of the pork man cutting tests.

Yes, and what's interesting is that straight swords are often more curved than we imagine, and curved swords are often more straight than we imagine.

When looking at examples of high-quality historical katanas, one will notice that many examples are only slightly curved.

And when looking at a double-edged symmetrical longsword, we imagine in our heads that it's straight. Curvature is added to the blade through tapering from the base to the tip of the blade. The angle of the blade relative to the handle is constantly changing depending on where the angle is being measured.

[chiselman]

I’m no expert by any means, but I think the key does lie in the blade length. The benefit the Wharncliffe blade gives really shines when you are looking at shorter blades that otherwise wouldn’t have the cutting power behind it. Box cutters are extremely effective at cutting. Knives like the Squarehead which is basically a box cutter in terms of edge shape and size are great cause all the power put into that short blade is focused at the tip. As you go up the chain though, I think the benefit starts to decline. Dragonfly, Delica up to the Yojimbo still can benefit from the shape due to their relatively small size but to me, at the point you get to the Yojimbo you start to have a loss of return. If you are talking slash cuts with a larger blade like a Endura, how much of the blade are you really using? As you stated, slicing is much more effective than chopping, and once the blade travels deeper into whatever material is being cut and the arc puts the knife more perpendicular to the material being cut, you start to get more into the realm of chopping rather than slicing, whereas the first 2-3 inches of blade benefitted from the extra slicing power. Now look at that same Endura length blade with a curve to it, and as the blade travels deeper into the material being cut, the curve allows the blade to keep its slicing motion throughout the arc rather than becoming perpendicular to the material at the same depth. I’m a huge fan of the Wharncliffe blade but to me, anything larger than say a Delica with a Wharncliffe blade kind of loses the benefit unless you are just looking for extra reach alone. Dragonfly Wharncliffe good. Military Wharncliffe bad.

Those are some great points. I think I would be extremely excited if something like a 4.5" wharncliffe was in the works! In the closed position maybe the length would be 5.5". If you think about how the knife occupies pocket space, an increase in blade length takes up more height but not necessarily any more width. Most pants pockets (at least for men) are deeper than 5.5" and the space in the pocket directly below where the knife is clipped is probably unused anyways. But I'm sure Sal & team have given production of larger knives plenty of thought and maybe there isn't the market for it given numerous regional blade length restrictions, lack of desire from consumers for something taking up a given amount of pocket space & weight to carry, and oversized blades not really aligning with the Spyderco brand. Or maybe that's why we have the Resilience.

[chiselman]

The Viking Seax is a kick butt looking blade.

It sure is!

[Michael Janich]

Interesting topic... thanks for posting.

First of all, there is a significant difference between the cutting mechanics of a sword and a knife. Once you have enough mass in a blade, it is capable of chopping cuts that work more like an axe--with the edge passing perpendicularly or nearly perpendicularly through the target. This is mechanically different than drawing the length of the edge through the target.

Because straight blades transfer energy into targets at right angles or nearly so, there is very little energy bleed. That also means that the impact shock of the cut is transferred completely into the wielder's arm. If you look at the history of swords, you'll see that many early swords were straight. This was partly due to the limited technology at the time, but also because those swords were used by men on foot. Once cavalry was introduced, straight swords gave way to curved ones, which dissipated the force of cuts delivered from horseback to allow the wielder to keep his arm attached when cutting from a moving horse.

Many styles of straight swords were also designed specifically for thrust-oriented tactics. Thrusting with a straight weapon provides greater accuracy. Thrusting with a curved weapon is certainly possible, but requires more skill and different mechanics.

Another deceptively simple reason for curved swords is that they allowed the user to draw a longer blade. Try to draw a long, straight sword our of a scabbard and you soon run out of arm. A curved blade complements the range of motion of the arm and allows the drawstroke. This was particularly important in the rise of iai-jutsu (the Japanese art of drawing and cutting in a single motion) and the transition from the dangling edge-down carry of the tachi sword to the more secure edge-up carry of the katana and wakizashi, thrust through the obi (sash).

One traditional straight-bladed weapon--the Filipino Kampilan--solved the problem of "drawing" in a unique way. Many kampilan scabbards consisted of two pieces that were held together by a thin cord wrap. Instead of drawing the blade, the user simply delivered the first "cut" with the blade in the scabbard. The edge would cut the cord so the scabbard pieces would fall away and it was "game on" from there.

Thanks again for a cool discussion.

Stay safe,

Mike

[sal]

Thanx Mike.

I might add that curved swords like a Katana depend more on the arc of the arm and the strike, as mentioned, offers a single point contact on the edge. A straight warncliffe blade with a sharp point is used more in a thrusting cut and the spine of the blade pushes the edge down widening the cut.

On the new "Swick" 5 design planned for production, I have opted to follow Mike's lead in using a warncliffe blade.

sal

[Tucson Tom]

Ignoring the business of swords. I am curious about this business of curved geometry versus a warncliffe like the Yojimbo in a small knife. I watched a video where Ernest Emerson is talking about the virtue of a knife with belly for cutting people and found what he said convincing -- and then I ran into the Yojimbo and found the arguments put forth there equally convincing. So at this point I am unsure what to think.

[Michael Janich]

Ignoring the business of swords. I am curious about this business of curved geometry versus a warncliffe like the Yojimbo in a small knife. I watched a video where Ernest Emerson is talking about the virtue of a knife with belly for cutting people and found what he said convincing -- and then I ran into the Yojimbo and found the arguments put forth there equally convincing. So at this point I am unsure what to think.

The common belief is that the longer the edge, the deeper the cut. Since belly allows more edge length to be included in a particular blade length than a straight edge, the common "wisdom" is that blades with belly cut more efficiently. I used to believe that too--until I stopped repeating the common wisdom and started actually doing cutting tests on relevant materials, like Pork Man. Depth of cut is a combination of drawing the edge through the target and the pressure applied into the target. This is particularly true on tissue, which compresses as you apply pressure to it, dissipating the force of the cut. Since the body generally moves in arcs, you have to look at the arc of motion of your hand and compare it to the arc, if any, of the cutting edge. The closer those two arcs are to parallel, the less pressure you apply and the shallower the cut.

Granted, my tests were on a pork target, which lacked blood pressure and the ability to contract like live muscle--both of which increase the firmness of the tissue and ease with which it is cut. Interestingly, during the 20 years that I wrote for Tactical Knives magazine, I had the opportunity to review several knives designed by Dr. Miguel D. Montagnese. Montagnese is a former Army infantry soldier turned surgeon turned knifemaker. When he was injured on active duty, he left the military, went to medical school and ultimately became a surgeon. Along the way, he did his residency at Akron City Hospital in Ohio, where he treated countless knife and gun wounds and became intimately familiar with the effects of weapons on the human body.

When the lingering effects of his military injury made it impossible for him to endure long hours in the operating room, Miguel took up knifemaking, choosing to design and make fighting knives suitable for today's infantrymen. Since he had LOTS of experience with knife and gunshot wounds and LOTS of experience cutting living human tissue, he also had some very strong opinions about what blade shape cuts tissue most effectively. The inspiration for his "11 Bravo" (11B--the MOS for infantryman) fighting knife was a #11 scalpel, the most precise and "aggressive" cutting tools he'd used in his medical career.

Here's a link to an excerpt from that article, which includes photos of his 11 Bravo design:

https://www.tactical-life.com/tactical- ... -11-bravo/

Since personal-defense knives may also be used for thrusting tactics, good blade designs should also allow the efficient penetration of skin and outer clothing. There have been numerous medical studies done analyzing the amount of force necessary to penetrate skin (here's one example: https://link.springer.com/content/pdf/1 ... 1702-7.pdf). Invariably, they have concluded that the ease with which a knife penetrates is determined by the radius of the tip. Knives with lots of belly try to penetrate with the leading edge of the blade--a large surface area. Wharncliffes have very acute points and penetrate almost effortlessly. As Sal noted, the "ramp" on the back of the blade also directs force toward the edge, opening the wound channel very efficiently by using the full length of the cutting edge as the blade goes deeper.

When it comes to fighting knife design, there is a lot of theory, common wisdom, and long-held belief that tends to shape people's ideas. Unfortunately, the accuracy of that body of information varies greatly. When in doubt, cut stuff, and figure our for yourself what works and what doesn't.

Stay safe,

Mike

[Tucson Tom]

When it comes to fighting knife design, there is a lot of theory, common wisdom, and long-held belief that tends to shape people's ideas. Unfortunately, the accuracy of that body of information varies greatly. When in doubt, cut stuff, and figure our for yourself what works and what doesn't.

Stay safe,

Mike

I appreciate you taking the time to answer in such a detailed way. As you say, a lot of "conventional wisdom" is just people repeating what they have heard and things cycling around. It is great to get real data and experience. Thanks very much.

[jdw]

My question would be why do we see historical swords from different world regions designed so differently? Is it the development of technology, different methods of warfare? Attack vs defense? This a fascinating thread.

Edit: And who came up with the idea of a fuller?

[Evil D]

My question would be why do we see historical swords from different world regions designed so differently? Is it the development of technology, different methods of warfare? Attack vs defense? This a fascinating thread.

Edit: And who came up with the idea of a fuller?

Probably all of those reasons from time to time and as technology advanced. For example once armor came into play, a sword that could thrust and penetrate became more important than a slashing/hacking weapon. It may also have had as much to do with your enemies as it did your own fighting style.


This is getting a little off topic but if anyone is interested in swords and swordfighting, you may find this interesting.

https://youtu.be/afqhBODc_8U

I've so read that in a lot of places swords were actually quite rare and/or generally extremely poor quality, and those who had them and had good ones were either wealthy or it was handed down through generations.

[mb1]

Interesting thread. Always enjoy reading your detailed and informative posts Mr. J.

Looking forward to the Swick 5!