[Lancelot Chan]

https://youtu.be/ZojpAF572A4
Using Longship swords to test out a combat cut on forearm difficulty target (thin wall PVC cored newspapers roll)

[Jean Thibodeau]

Impressive cutting skills, my personal experience is limited to only a few occasions when my defunct HEMA group went to a farm belonging to relatives of one of our instructors to do some fun cutting on mostly pumpkins .... So not very challenging targets since even the blunted swords could cut the pumpkins.

So with the above disclaimer about my personal skill level or experience with test cutting this does seem rather efficiently well done ..... Well, I've seen your test cutting videos before, so I's not really surprised.

Now, I think that a lot has to do with getting edge alignment perfect and it's smooth acceleration and speed that does the cutting as well as letting the sword's built up inertia and weight do the cutting as opposed to muscling a cut using too much power, this fails as it turns into a power push with insufficient speed ?

Oh, and sharp and durable edges certainly also help !

Even when I test an edge that I just sharpened on a piece of paper held in one hand with sword or knife in the other, getting the right edge alignment is critical as well as the angle of the cut so that the thin sheet of paper doesn't fold because the edge didn't start the cut into the paper properly, a good razor sharp edge can still fail to cut if one does it badly and defining how one does a good hand held paper cut is hard to define ..... Years of practice can make even a so-so edge still cut the paper, and a badly controlled cut with a razor edge still fail ..... It all seems to be in the smoothness of the acceleration I think, and to a degree believing that the cut will succeed, with self doubt smoothness can go south so there is a psychological element to a successful cut because hesitations due to lack in confidence can lead to sabotaging one's cuts ?

[Lancelot Chan]

Thanks for watching. There are several factors weighing in the equation. Above all is the blade alignment. As you've mentioned, with perfect blade alignment, even a so-so sharpness will cut paper. On the other hand, with bad blade alignment, not only will one not able to cut with the sword but more importantly one will damage the edge and the blade in the bad cut. Such damage may not be repairable, like twisting the blade.

The second important factor is sharpness. Sharpness came in 2 forms. One is geometrical sharpness, which is the cross section shape and edge angle. The other is the degree of polish. The higher degree of polish, the keener the apex would become. One can have a very aggressive edge angle (like 10 degree per side) but still get away at cutting bone-like subjects as long as there's a larger degree micro bevel (30 to 40 degree per side) at the apex done at very high polish to make sure it's keen yet robust. On the other hand, one could have a slightly larger degree of edge angle (20 degree per side) but not as much a micro bevel (25 degree per side), and still get damaged in the same target while suffering more resistance in the cut. So if you ask me, I would go for the former setup than the later one. I tried both and figured that out.

The third important factor is the sword's balance. Balance comes in the third place, or to be more accurate, the moment of inertia. Since swords with the same balance point can still have different moment of inertia. Given the same sharpness, the more forward the inertia, the more likely the sword will cut through something resisting since it has more inertia to store up your power at the acceleration stage, and more momentum to go through the target after the impact. A lighter faster sword will accelerate faster, but get itself stuck in a substantial target like Tengu did, while the heavier sword will take longer to get the speed up but maintain it better cutting through the target, thus more likely to cut through completely. That's not to say cutting into the bone isn't an effective strike in itself.

The forth important factor is the "slice". As you also mentioned, a powerful push into the target isn't going to cut. Actually, even a fast and powerful push wouldn't work. It takes a little bit of "slicing" to make the cut feels a lot less resisting. A curved blade will help in this matter but a straight blade can do too if the user know how to make the "slice" happen. One has to resist from pushing the blade into the target or throwing the tip out as some suggested in "casting the sword out" cuts, but lead with the hilt and drag the hilt to the finishing point. The blade will still hit the target but at a slicing angle this way, causing a much smoother and stronger cut, despite carrying less impacting power. One need to leave room around the body for the hilt to move into quickly, in order to facilitate the "slice". I don't see this being commonly done in other styles.

The fifth important factor is the "speed". Speed is less important if the target is very sturdy and resisting, but very important if the target is light and would fly away upon impact. For a realistic human like target, you don't have to push ur speed to the max in order to make a cut happen. But most of us are cutting much lighter weight targets, thus the emphasis on speed become more than a real life application would be. Heavier swords would have less top speed and longer acceleration distance. These swords would not do good in modern cutting activity, but would do a lot better in actual combat due to the target's weight and resistance difference. A lighter, very sharp and fast moving sword will still get stopped by heavy clothing on a person, while the heavier slower moving sword with the same sharpness, will carry enough momentum to go way deeper. Modern targets on cutting stand would just get toppled over under the same strike, though. To be energy saving, the top speed zone should be placed on just before the moment of impact, for a better cutting through opportunity. For that, you can see many swordsmanship strikes with the top speed zone located on top of the head, or even behind the head (like zwerchhau was), were not meant to be a decisive cut.

Hope you enjoy the long reply. LOL.