[Eric G.]

Hello friends,

I have a question that I think could turn into an interesting discussion here. I have been thinking about this for a while. To begin, my premise is that the distinction that makes a blade a good cutter or good thruster depends largely on its cross-section. For the sake of simplicity, let’s limit this to double-edged straight blades only, no katanas, flachions, falcatas, yataghans etc. I know that there are other factors to consider (many many factors, I’m sure) but I think that I am correct in saying that the cross-section is the number 1 factor when determining the cut and thrust capabilities of the sword. Is that correct? So what cross section makes the most effective cutter and why? When I first thought of this I listed the first ones that came to mind in order from best to worst. My list looked like this:

1) lenticular
2) flattened diamond
3) hollow ground

But then I realized that I left out the hexagonal cross-section. At first I didn’t know where to put these, but then I remembered that most atrims (which are renowned for their cutting awesomeness) are hexagonal in cross section. Again, I know that there is more to it than cross section, but under my premise that the cross section is the factor that gives the most weight to the cutting ability of the blade I could re-do my list like this:

1) hexagonal
2) lenticular
3) flattened diamond
4) hollow ground

Feel free to make your own list to correct mine. I know that many of you have much more experience than I do.

So my main question is this: why? Why do these different cross sections make such a difference? I would be interested to hear your thoughts on how the blade interacts with the target from the moment that it makes contact until it ceases to make contact, and how the cross section makes that seemingly critical difference.

Thanks all.

[Nathan Robinson]

Cutting what? What are you cutting? What's the medium? Swords are designed for different purposes and part of this is the medium against which they're intended to cut.

[Luka Borscak]

There is much more to this. Lenticular slides through target easier, but hexagonal and diamond are stiffer and stiffness is underestimated factor in cutting potential... Ideal blade for cutting would be thin, lenticular and very stiff, but that is unfortunately not really possible so we have to do with trade offs. So good cutting is either achieved with as thin as possible but still stiff enough hexagonal or diamond section or with thin and lenticular but flexible blade. And that all is without including in the mass distribution, mass itself, point of balance, percussion point and so on...

[Bartek Strojek]

[Timo Nieminen]

The question of "why is the katana the best sword, ever" has generated many replies to the question of what is the best cross-section for cutting. Apart from the obvious points like "thin is good", the katana-question tends to focus on the practical value of the ridge-line.

The question focusses on the cutting of flesh or similar tissue, and substitutes used in cutting exercises. In this case, viscous drag is a major loss of energy as you cut through the target. How to minimise drag?

Thin is good, because you need to displace less material sideways. But narrow (i.e., the front-to-back width of the blade) is good too, since this also reduces drag (witness Turkish and Korean use of short arrows - shorter than the draw length - for long range). So, the best profile would be a narrow, thin razor blade. But with the limits of steel, this is too floppy and weak. So you need enough thickness and width for strength.

Tissue and substitute cutting media are not liquid, despite being wet. Supposedly, the ridgeline allows the blade, past the ridgeline, to avoid contact with the cutting medium, and thus reduce drag. Ridgeline too close to the edge will meant that the edge angle will be large, so the blade won't be sharp enough. So, the compromise is to have the ridgeline back far enough to have an acute enough edge angle for good sharpness, but no further.

Anyway, that is the standard wisdom, aimed at justifying the superiority of the katana. Seems like the kind of thing that might be testable, with a high speed camera, or perhaps computationally.

Applying these ideas to a straight double-edged blade, hexagonal section looks best, out of non-fullered blades. Lenticular with a shallow broad fuller should be good, too, maybe better.

A convex edge ("niku" on the katana) might help, but this is usually explained as strengthening the edge. But consider the convex nose of the tuna, an excellently low-drag fish. (For cutting through liquids, the tuna-section blade would be ideal.)

[Eric G.]

[J.D. Crawford]

[Vincent Le Chevalier]

The two basic variables that I'm aware of are edge angle (a more acute angle will be sharper, more efficient in slices, but more fragile) and blade thickness (the thicker the blade, the more energy will be needed to move it through). These two have direct local effects on the cutting behaviour. The influence of drag according to the shape is of second order in my opinion, possibly negligible compared to the angle at which the blade hits, which creates a "guillotine effect"...

Concave faces (hollow grinding, fullers) in my understanding are mostly there to play with stiffness and mass distribution. Of course both have an influence on cutting, but you can't just consider the local cross-section where the blade meets the target; it's the evolution of the dimensions and shape of the whole blade that determine these factors. Not all blades have uniform cross-sections, practically none have constant thickness, so it becomes complicated real fast

Regards,

[Timo Nieminen]

[Michael Edelson]

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<----does this avatar make me look fat? How about cocky and obnoxioius? I think so.


Anywho...

I don't think cross section is the end all and be all. Mass behind the cutting edge plays a big role (though some might consider that the same thing). Cross section is tricky. As others may have said (I am far too lazy to read the entire thread), thin is good, but stiff is better, thin and stiff is best.

e.g.:
XVa are stiff but lack mass behind the cutting edge and are thick
XIIa and XIIIa are thin and have mass but flex too much which robs energy

An ideal super duper sword would have a good deal of mass behind the cutting edge, be stiff as a board, be thin enough to easily pass through the target and have a nice sharp edge.

[Nat Lamb]

“Blade Harmonics” are another (very important) thing to consider, and they are going to be very dependent on cross section ( and related to, but not the same thing as stiffness). I don’t have all that much cutting experience, but it doesn’t take much experience to have encountered a cut against a slightly less forgiving medium where the edge alignment was good, swing “felt” solid, but you contact with the wrong part of the sword and “boing” you just bat the thing out of the way or get a jarring mis-hit. Where the relative sweat-spots are on a blade will rely on cross section, but in a way that is really hard to calculate without some pretty advanced engineering software. I have a suspicion that even 2 swords of identical weight distribution will behave differently with a hit at point x depending on cross section, and vice versa, that 2 swords with identical cross sections but different weight distribution will function very differently, even striking with comparable points on the blade.

[Aleksei Sosnovski]

A lot has been said here about mass, thickness, stiffness and acuity being far more important than blade cross section. But here are my 2 cents.

IMHO lenticular, diamond and hexagonal cross sections are more or less equal in performance if their thickness and edge acuity are comparable. Take a diamond cross section, round the ridge and you get a lenticular cross section. Grind the ridge flat and you get a hexagonal cross section. Choice of these cross sections (in case of cut-oriented swords) seems to depend more on desired width and thickness of the blade rather than anything else. Making a wide thin blade with diamond cross section with well-defined center ridge would be quite difficult so lenticular cross section is the choice. Or, if one wants a less acute but more durable edge, he would go for hexagonal cross section, possibly with somewhat smoothed ridges. However if the blade should be narrow making it lenticular or hexagonal will result in edges less acute than desired, so diamond is the choice. For a blade of average width and thickness any cross section can be chosen depending on whatever looks better.

Now a hollow-ground cross-section is entirely different. The more such blade goes into the cutting medium, the more resistance it faces. Not a good thing. From my personal experience knives with hollow-ground blades cut worse than knives of otherwise comparable geometry but with triangle cross section (and of course some secondary bevel). The reason for hollow-ground blades is to create a very stiff but light (in case of rapiers and smallswords) or wide (in case of a cut-and-thrust swords) blade. So generally hollow-ground sword blades would be thicker than blades with other cross sections. However hollow-ground sword blade would be wider than equally thick blade of other cross section and therefore would cut better. Another purely aesthetical reason for hollow grinding may be to create a wide cutting blade with well-defined central ridge (something very difficult to achieve with diamond cross section as I already stated above).

And about drag. It sure does have some effect. Just try cutting some large piece of meat with a wide chef's knife and then do the same but using a narrow fillet knife. However I don't think it would make much difference unless one tries to cut very thick but soft target which can't be found in a normal human body.

[J.D. Crawford]

[Gary Teuscher]

[Luka Borscak]

[Chad Arnow]

[Michael Edelson]

[Matthew P. Adams]

Michael,
Are you sure you would "never" post? I would think that if you found a topic interesting and or had strong feelings about it, that you might post. You'd be on surer ground if you said "rarely" or even "less likely too," or better yet, "probably would not." The only absolute in most of this is that speaking in absolutes is dangerous.

Chad,
Sorry, I just couldn't resist. You are, of course, "absolutely" correct!

[Chad Arnow]

[Nat Lamb]

with regards to the disagreement (obviously friendly) between Chad and Michael, I would like to weigh in and say you are both right. As someone with a background in philosphy and hermeneutics (though not spelling...) I would say that it is indeed usually worth the extra words to increase precision, but in this particular case Michael said Type XVa are stiff" not "XVa's are stiff", meaning that his statement should most properly be interpreted as discussing the "type" not "examples of the type. This may seem like a very, very small distinction, but because swords are representitives of a type to the extent they match what is "typical" of that type, such a statement can be considered to include they qualifyer as a given. [/b]