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Post by kclee008 on Jun 2, 2023 16:35:34 GMT
What are the benefits of a hollow grind blade? I assume more rigidity for thrusting. Any other major benefits over other blade geometries? Or mostly aesthetics?
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Post by AndiTheBarvarian on Jun 2, 2023 17:04:39 GMT
Less weight compared to a diamond cross section or convex forged blade with the same width and thickness. Not more rigidity than those but more rigidity than a blade with the same mass but the other blade types. And a sharp edge angle for cutting.
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Post by mrstabby on Jun 2, 2023 17:56:14 GMT
A hollow grind has less resistance when cutting, theoretically. No idea if you would really feel it. Theoretically the concave blade has less thickness most of the way to the middle ridge or fuller than a flat ground one, you can definately feel the difference on a knife when cutting fruit or vegetables, but as I mentioned I can't say for swords. You would need to have the same sword, once flat, once hollow to really tell. It would also depend on the depth of the grind. I have seen blades sold with an advertised hollow grind where it is like a hair when you put a ruler on top.
I have read the opposite, that hollow ground blades are more flexible than straight grinds. Diamond and octagonal are the most rigid.
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Post by AndiTheBarvarian on Jun 2, 2023 18:07:39 GMT
The important point is "same mass". A blade with diamond or convex cross section and (!) the same mass is less wide and broad, and less rigid. A blade with diamond or convex cross section with the same width and thickness as a hollow grind blade is more rigid but much heavier. It's the same with fullers, hollow grind blades just have four fullers instead of two.
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Post by mrstabby on Jun 2, 2023 19:32:22 GMT
Fullers are a bit different because of their shape and placement (they need to be quite deep to have a measurable effect on stiffness). I doubt a hollow grind will stiffen a blade to the extent a deep fuller does, but you would need the exact same sword, with the same weight, one hollow, one flat to prove that. More like it won't hurt performance vs a straight diamond. You also have to keep in mind not every hollow grind is done well.
One thing that I am positive about, they are easier to damage than flat grinds, especially if they are very thin behind the edge. Better cutting performance, higher risk of rolling or breaking. Also hollow ground and fullered blades are easier to twist than a diamond.
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Post by AndiTheBarvarian on Jun 2, 2023 19:56:47 GMT
Stiffness has a direct relation to the square area but to the width in 3rd power afaik. Double wide, eight times stiffer. Of course a thin sharp angled edge is more fragile than one with niku. But those swords were designed to thrust through mail and hurt a man with cutting also.
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Post by mrstabby on Jun 2, 2023 20:06:09 GMT
I only know it is related to thickness perpendicular to the force (just looked, thats the x^3 formula you mentioned). And a fuller will double the ridges, its like having two rods connected side by side instead of one slightly thicker one, which will be stiffer. Do we speak side to side or paralell to the edge? I think we might be talking about different stiffness. For me it means how hard the blade is to flex when thrusting. And the thrusting blades are more likely diamond to concentrate mass at the center, like an ice pick, while cutters are more likely to have fullers to widen the blade like a knife.
EDIT: there is also a difference if we are talking double or single edge. On a single edged weapon the grind will probably have less effect on stiffness than spine thickness.
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Post by AndiTheBarvarian on Jun 2, 2023 20:27:01 GMT
You're still ignoring the mass problem. A tube or a cross are stiffer than a solid round rod with the same square area, or the same mass of a certain length.
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Post by mrstabby on Jun 2, 2023 20:29:58 GMT
You're still ignoring the mass problem. How so?
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Post by AndiTheBarvarian on Jun 2, 2023 20:30:51 GMT
My edit.
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Post by mrstabby on Jun 2, 2023 20:34:45 GMT
But a hollow grind is neither an x or a tube. Its a slight curve at best. To stiffen the blade it would have to be thinner in the middle than on the edge, which is just not the case for most hollows.
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Post by AndiTheBarvarian on Jun 2, 2023 20:42:15 GMT
In principle a hollow grind blade is a +. In real life it's rather diamond, that's why there's not much difference. At least on my Windlass Erbach.
The idea is very old btw, bronze swords had a mid ridge on the blade for the same reason. And also not very old, smallswords had threefoil blades for stiffness combined with extreme lightweight.
Or look at H-beams.
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Post by mrstabby on Jun 2, 2023 20:52:55 GMT
It is mostly done to get a wider blade with the same mass and maximum thickness for better cutting with the same stiffness, but a real cross shape would hinder cutting more than anything. There are cross shaped blades, bayonets mostly, but you wont be able to cut with them even when they have a sharp edge. There is a minimum radius the grind/fuller needs to be to be stiffening. I very much doubt a hollow grind, that wasnt at least a fifth of a circle would add stiffness. You can try it with paper, it will only stiffen up when you bend it to a certain degree.
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Post by AndiTheBarvarian on Jun 2, 2023 20:54:59 GMT
"same stiffness" is the magic word. The cross/+ is a physical principle for stiffness. Forging a sword blade has more aspects.
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Post by mrstabby on Jun 2, 2023 20:57:16 GMT
In principle a hollow grind blade is a +. In real life it's rather diamond, that's why there's not much difference. At least on my Windlass Erbach. The idea is very old btw, bronze swords had a mid ridge on the blade for the same reason. And also not very old, smallswords had threefoil blades for stiffness combined with extreme lightweight. Or look at H-beams. Yeah, but a mid ridge isn't technically a hollow grind. And triangular is something different entirely. An H beam comes up again on both sides, this makes it work, like a fuller, but no hollow grind will be that deep, except on blunt training swords, that have a strenghened edge profile.
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Post by mrstabby on Jun 2, 2023 20:58:04 GMT
"same stiffness" is the magic word. The stiffness here comes from the middle ridge thickness, not the hollow grind. You need to either thicken the ridge or add ridges for strength, a fuller does the second, a hollow grind does not.
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Post by AndiTheBarvarian on Jun 2, 2023 21:02:27 GMT
You can see the cross or the missing squares, it's the same. A hollow grind thickens (or should thicken) the ridge of a blade with the same mass/square area.
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Post by mrstabby on Jun 2, 2023 21:20:59 GMT
You can see the cross or the missing squares, it's the same. A hollow grind thickens (or should thicken) the ridge of a blade with the same mass/square area. Yes, either you thicken the spine for added stiffness at the same width or widen the blade for cutting power with the same stiffness, but its not the grind that stiffens it alone, its the change in thickness. When you widen the blade, you gain no stiffness. Fullers will stiffen up the blade by their geometry alone (speaking of everything being done well). But a diamond that is of the same mass, but less wide will be as stiff as the same thickness hollow grind, but the diamond will be better at penetrating armor than a hollow grind (less resistance).
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Post by AndiTheBarvarian on Jun 2, 2023 21:27:49 GMT
Sorry, I'm tired, you're right, hollow grind makes absolutely no sense, that's the reason why hollow grind blades never existed.
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Post by mrstabby on Jun 2, 2023 21:32:22 GMT
Sorry, I'm tired, you're right, hollow grind makes absolutely no sense, that's the reason why hollow grind blades never existed. Not what I say at all, just stiffness does not depend on the edge geometry but the spine thickness. And you said something about same thickness, so I assumed same thickness. But yes, it is late and I might have misunderstood something.
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