Convex Edge Geometry Slide Show

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Convex Edge Geometry Slide Show

Postby KyleyHarris » Sun Jun 20, 2010 9:52 pm

Hello Everyone.
In relation to my comments on the other post Sharpness & Application Previous Post I wanted to make a slide show to open a dialog about different edge geometries of swords. I have not handled any Authentic Chinese Period swords, but I do know a lot about edges :) so.. Hopefully with this information we can create an interesting topic and look at many different swords of the past, and future to generate conclusions as to how they might have been used.

Here is a link to the video slideshow. Blade Geometry Slideshow on youtube which I will also link here as photos for ease of reading. The slide show is just a nice quick way to see where I am heading. Original Image gallery because the forum is chopping the sides off where the text is.

Enjoy, and discuss. Thanks.

One important thing I wanted to broach was comments read regarding the risk of deflection on a convex edge in cutting. Which is very true. Normally we practice cutting as close to 45 degree angles as we can because its natural, and its the path of least resistance in targets such as bamboo. Much harder to cut it on the horizontal plane. but with heavier convexes, especially armor piercing ones the convex bevels can be heavy enough to prevent a 45 degree cut and you end up with an action like throwing a pebble on a lake.. instead of sinking the smooth surface can bounce off. This means that we need to adjust our cutting angles and techniques for different blade styles.

Thanks for reading.
Please take a good look at the zoomed in angles of the cut. All of these are at exact 45 degree entry. As the Acute angle of the cutting edge gets wider and more durable you can see that there is a disproportionate amount of steel on the top bevel egress compared to the lower bevel. This is why deflection is worse with thicker edges. The Cutting angle must be reduced from 45 degrees to make the entry angles of both bevels more proportionate and reduce the risk of deflection.

On a target like a real human being, or Armor (which is the real purpose of a sword) the Angle of attack is arbitrary because what we are cutting does not have a grain which is tougher in any particular direction (until you hit a bone).

When cutting wood, and bamboo the bamboo and wood has a cross sectional grain that is incredible tough to cut. when splitting wood we always go down the grain, rather than across because of this toughness. This leads to the assumption that a convex edge requires more force to cut.. in fact.. the reality is more (i feel) that we have to lower the angle of the edge and go more against the grain in the bamboo, which is inherently harder to do and leads to the feeling that its less sharp.

By testing on Carcasses and other objects that do not have a grain then we can get a better understanding of how the edge geometries will really perform in real use. (not that this is too easy to do unless you work for Cold Steel)



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KyleyHarris
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Re: Convex Edge Geometry Slide Show

Postby Scott M. Rodell » Tue Jun 22, 2010 9:15 am

KyleyHarris wrote:.... I have not handled any Authentic Chinese Period swords, but I do know a lot about edges ...


Thanks for the excellent graphics & overall presentation... In regards to Chinese Swords, both jian & dao, we encounter all three types of convex grinds. Naturally, we assume this has to do with different jobs in mind, i.e. battlefield use where one expects to encounter armor to civilian use where one would prefer a "sharper" edge that could more easily slice thru cloth.

Some ideas about how one might have wanted to cut are discussed in the thread - Some Thoughts on Liao.
http://forum.grtc.org/viewtopic.php?f=4&t=285&hilit=Some+Liao+some+thoughts+on+liao

KyleyHarris wrote:.... One important thing... the risk of deflection on a convex edge in cutting. Which is very true. Normally we practice cutting as close to 45 degree angles as we can because its natural, and its the path of least resistance in targets such as bamboo. Much harder to cut it on the horizontal plane. but with heavier convexes, especially armor piercing ones the convex bevels can be heavy enough to prevent a 45 degree cut and you end up with an action like throwing a pebble on a lake... can bounce off...


Thanks for reminding readers of this possibility. Before anyone begins work with hard targets, like bamboo or hard wood, they should spend many, many hours with soft target to make sure they have "mastered" control of the entire cut. The follow thru after the cut is generally the hardest part of the cut to control & I have unfortunately, repeatedly, observed that almost no one pays any attention to the blade action after the cut has past thru the target. If you can not control the after-cut swing of your weapon, you will likely cut your leg if the blade skips off the surface of a hard target.

KyleyHarris wrote:.... By testing on Carcasses and other objects that do not have a grain then we can get a better understanding of how the edge geometries will really perform in real use. (not that this is too easy to do unless you work for Cold Steel)


Indeed! I hope they have barbecue after there cutting sessions... :wink:
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Re: Convex Edge Geometry Slide Show

Postby KyleyHarris » Tue Jun 22, 2010 10:51 pm

Thanks for that Link. I'll read it carefully later, but it seems to corroborate much of my own thoughts and testing.

Thanks for reminding readers of this possibility. Before anyone begins work with hard targets, like bamboo or hard wood, they should spend many, many hours with soft target to make sure they have "mastered" control of the entire cut. The follow thru after the cut is generally the hardest part of the cut to control & I have unfortunately, repeatedly, observed that almost no one pays any attention to the blade action after the cut has past thru the target. If you can not control the after-cut swing of your weapon, you will likely cut your leg if the blade skips off the surface of a hard target.

Yes, I agree. Cutting Bamboo is really not hard, as long as your focus and precision are on.. but (as I know myself) even a small lack of focus and it will bounce or derail down the centre. This is why I am a big fan of impact forms testing using a wooden sword against a tree so that your arm creates the ability to hold clear angle at impact.

I've added another video, and linked it under maintenance also. Finding and Honing the Convex Edge but it kind of goes
hand in hand here also. as by determining the edge acuteness of the convex and the spine height at contact you can also get a good feel for how the edge will perform.

The video mixes the Slides with demonstration, but I'll include the images here also. These presentations do take an hour or two to make, so I sure hope they are of value to people here. Primarily I made this one for my youtube viewers and owners of my own work, as its all convex. In application with a sword its no different at all, except for the extra care and handling required of a long double edged blade.

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Re: Convex Edge Geometry Slide Show

Postby KyleyHarris » Tue Jun 29, 2010 4:46 am

I read this very good Article yesterday about Niku on Japanese swords.. Niku refers to the thickness and body of the blade.. in effect.. the Convex nature of the body.. more Niku means more Convex and more steel.. so stronger.

Good Article

Although its in reference to Japanese Swords, the issues and practical application are the same. It refers to the differences between Flat grind (no niku) and convex (niku) and clearly explains a point I made in another thread. That point being that flat ground blades create more Drag from friction than they do improvements in sharpness.. so although they are sharper in soft small targets.. in bigger targets the friction slows the blade down more than the sharpness compensates. where-as the convex has less drag, so cuts more easily even though the initial entry may be more difficult for some.
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