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

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

#21

Post by chiselman »

Thanks to everyone, and especially Sal and MJ, for their insights!
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Re: Yojimbo 2 wharncliffe with straight edge vs. curved sword cutting philosophy

#22

Post by TomH »

Lots of good info here. Thanks, Michael Janich.

Also looking forward to the Swick 5.
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Re: Yojimbo 2 wharncliffe with straight edge vs. curved sword cutting philosophy

#23

Post by Pelagic »

The belly of a blade decreases the amount of surface area (apex) making contact with what you're cutting, increasing pressure. Same as a pointy tip: less surface area, more PSI is applied, which means less pressure exerted by the user. Cuts become significantly easier. The same happens with the tip of a reverse tanto, sheepsfoot, or wharncliffe blade. When you're using the tip (like when opening a package), due to the straight edge shape of the blade, only the very tip is touching what you're cutting, increasing pressure, thus less pressure for you. It's also easy to apply more pressure if necessary (press down on spine or thumb ramp) due to how you'd be holding a knife. Try this on a K2 for example, and the presence of a large belly don't make this nearly as easy.
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ferider
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Re: Yojimbo 2 wharncliffe with straight edge vs. curved sword cutting philosophy

#24

Post by ferider »

Michael Janich wrote:
Tue Jul 23, 2019 7:52 am
.... 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.

: : :

Mike
Interesting discussion. Mike, I always wanted to ask you the following: say you have a Wharncliffe and a Bowie, with similar edges and spine thickness and similar tip angles. You see any difference in penetration capability ? Seems to me the Bowie would penetrate a little deeper, while the Wharnie would penetrate a little less but also slice down.

Thanks,

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

#25

Post by Ngati Pom »

Interesting thread, it seems to me, after looking at Mr Janich's post on the 11 Bravo knife and reading Sal's on the Yojimbo design, that the broad head arrow relies on a similar geometry to achieve pretty much the same effect. All be it more focused/localised.
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Re: Yojimbo 2 wharncliffe with straight edge vs. curved sword cutting philosophy

#26

Post by Michael Janich »

ferider wrote:
Wed Jul 24, 2019 9:42 am
Interesting discussion. Mike, I always wanted to ask you the following: say you have a Wharncliffe and a Bowie, with similar edges and spine thickness and similar tip angles. You see any difference in penetration capability ? Seems to me the Bowie would penetrate a little deeper, while the Wharnie would penetrate a little less but also slice down.

Thanks,

Roland.
A number of years ago, I tried to compare the penetration abilities of various blade shapes (and wrote a column about it for the now-defunct Tactical Knives magazine). To do it as empirically as possible, I made a ballistic pendulum from a length of heavy PVC tubing and used a T connector at the end to fashion a fixture to hold the knives. I hung the pendulum from a rafter in my garage and used a foam mannequin dummy secured to a Black and Decker Workmate base as a target. The dense foam of the mannequin provided a consistent, homogeneous, but dense target material that would stop the penetration of the blades within a few inches.

I made sure to always raise the pendulum to the same height before releasing to ensure a consistent impact force. I also made sure to hit a fresh spot on the mannequin, so there as no way the blade would hit an existing puncture channel that would reduce the resistance of its penetration. When the blade stuck, I'd mark it at the surface of the dummy, withdraw the blade, and measure the depth of penetration. I repeated the test multiple times with each blade style and calculated an average.

Most of the testing involved fixed-blade knives with blades roughly six inches in length. I found the dagger (a Gerber Mark II) penetrated deepest. Conventional blade designs with some belly, like Bowies (with unsharpened swedges, not false edges) and a Japanese aikuchi, came in second, and American-style tantos with ultra-strong points offered the shallowest penetration.

Just for the **** of it, I also decided to try a Wharncliffe--a first-generation Yojimbo that was my carry knife at the time. I chucked it up in the pendulum fixture, raised it up, let go, and watched as the knife appeared to "bounce off" the mannequin. Closer examination of the mannequin showed that there was indeed a puncture hole, but the blade did not "stick" and stop in the target like the others I had tested. To try to determine the depth of penetration, I colored the blade with dry erase marker and tried again. When the blade bounced back, the marker was wiped clean all the way to the front of the handle. The Wharncliffe blade was penetrating so cleanly and with so little resistance it was hitting the front of the handle and bouncing right back out. Unfortunately, I didn't have a six-inch Wharnie blade in my collection to do a straight-up comparison with the other knives, but clearly, the Wharnie penetrates extremely well.

As I noted in a previous post, medical studies using actual human cadavers, as well as tissue analogs like pig skin, have shown that the force needed to penetrate skin is directly related to the acuteness and surface area of the knife's point. Any blade design that "leads" with the cutting edge will experience greater resistance. Since a Wharncliffe does not lead with the edge, it arguably has the most acute point of any conceivable knife design. Other point profiles can approach it, but not equal it.

Even then, the force necessary to penetrate skin--even with less efficient, less acute blade shapes--is far less than most people think and a fraction of the force most people are capable of generating. As such, your ability to perceive subtle performance differences is limited. Once you add clothing to the mix, however, the dynamics change again. In my experience, the Wharncliffe once again rises to the top.

I hope this helps.

Stay safe,

Mike
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ferider
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Re: Yojimbo 2 wharncliffe with straight edge vs. curved sword cutting philosophy

#27

Post by ferider »

Thanks a lot for the thorough reply, Mike, and a great experiment !
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Re: Yojimbo 2 wharncliffe with straight edge vs. curved sword cutting philosophy

#28

Post by Donut »

I wonder if this is more related to: Is your sharpened edge better at push cutting (a straight edge would push cut better) or slicing (a curved edge would slice cut better).

In reality, this is just the Yojimbo 2 versus the PPT.
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