Please forgive what may be a rather stupid/obvious question; I'm in all senses a "newbie" seeking to learn.
I always assumed that a properly sharpened knife could be expected to cut perfectly vertically, without tilting its axis nor exerting any uneven force left or right. If that is correct, why would it make any difference if someone who was left handed used a knife that was supposedly designed for a right handed person -- or vice versa?
based on how the knife is ground say a 90/10 righty bias would cut the food a certain way since you are a righty, same thing as a lefty
Originally Posted by larrybard
Sorry, but I still don't understand. Are you saying my assumption is incorrect that a righty and lefty would each make almost perfectly vertical cuts, but rather either be naturally canting the blade to one side or the other, or pushing (consciously or unconsciously) the blade slightly to the left or right (while keeping its axis vertical)?
Originally Posted by CoqaVin
what I am trying to say is based on the way the knife is ground and if the person is lefty or righty, the food will cut a certain way due to the night being ground a certain way, think of a single bevel knife
I don't know if I can explain it properly, but I'll try.
In my experience it's not so much to do with the cutting edge itself (which is almost microscopic), but rather the angle of the bevels that cause steering. When you cut something with a knife you exert force on the food, and the food exerts force back. Now the food isn't just pushing up trying to resist the knife, it's also pushing sideways on the knife (blade face) as the knife travels through the food. So while you're pushing down with the knife, the food pushes back on the sides of the blade and that's what can cause steering. Asymmetric bevels do exert uneven force left or right. Grind can also cause steering mind you, as in the case of a yanagi.
A yanagi is an extreme example. It's single beveled, 100/0 grind. Yang's also have an ura (a concave or hollowed-out side). This makes them wicked sharp for slicing, but I wouldn't dream of cutting a big sweet potato with one. Just based on the way it's ground with 1 giant bevel and a hollow on the other side, it'll steer because of the way the food exerts force unevenly on the 2 different sides. Can a lefty use a righty knife? Absolutely. It just won't necessarily behave as intended and the user might have to anticipate and compensate for it.
If I'm off on this guys and gals feel free to correct me.
EDIT: Here's a pic that might help (or might not). Just picture food trying to exert force on each side, you can imagine how different the force on each side would be.
EDIT 2: Here's another one:
Your explanation helps me understand -- a little. I will accept that an asymmetric bevel will, as you state, exert uneven force left or right. But -- and maybe I have this backwards -- that would mean that a righty using a "righty" knife would find that even if holding the knife perfectly vertically and slicing down vertically the knife would tend to drift to the right (?) through the slicing action. But why wouldn't exactly the same effect be felt by a lefty -- i.e., the knife would tend to drift to the right for the lefty's as well? And if, as a consequence of this force, the righty would gently, and perhaps not consciously, exert an offsetting force to the left to counteract this drift, it seems to me the same thing would be done by the lefty using the very same knife.
It's maybe best to think about it in terms of biomechanics. When you push downwards in any cutting action, the hand is not moving completely vertical but instead is following an almost imperceptible inwards arc. In essence, a neutral ground knife would not have any effect, a knife ground for the appropriate hand would counteract the arcing and an opposite ground knife would accentuate it. This is of course assuming proper sharpening and it should be noted that with practice and modified technique it can be overcome.
You can modify your technique to make an opposite ground knife work for you, but if you just allow your hand to follow it's natural path then you will generally experience steering.
The exact same action would be felt by a lefty. After all, the same force would be pushing on the blade face regardless of which hand it's in. The problem is in how you'd expect a knife to behave. If a lefty is used to using a left-handed knife, and then picked up a righty, it would behave differently than they're used to. The lefty would be used to the left feeling knife, and so would have to compensate to accommodate the new feel. It would just feel off.
Like MAS4T0 said, there's a small twist of the hand when cutting. While not exactly what we're talking about (since the video describes serrated knives) it might help to explain through visuals what's kind of going on in regards to how the hand twists.
So imagine a single-bevel knifed which already has steering problems just based on design, used with the wrong hand it would compound the issue. A lefty using a righty wouldn't get the clean, consistent cuts as they would using the appropriate handed knife.
I'm grateful for your explanations, and I think I now get it. First, due to the geometry of an asymmetric blade, a lateral (horizontal) force naturally results from a purely vertical cutting motion through materials. (And, although I don't think you've specifically said so, there may also be a torsional/rotational force created by the geometry.) Second, as a result of what one might describe as human geometry/biomechanics, there is also a natural tendency of the individual to exert a similar torsion/rotation to the blade while cutting. Presumably any rotational force resulting from the blade geometry would, ideally, in a perfectly shaped asymmetric blade, exactly offset any natural tendency of the individual to rotate the blade. However, those two effects would instead likely reinforce and exacerbate the rotational effects in a asymmetric blade designed for a righty but wielded by a lefty (or vice versa).
I suppose that if steering is defined to mean any deviation from a purely vertical cut, then even if there were no rotational force resulting from asymmetric blade geometry, the purely lateral uneven force would also result in steering as the blade cut a path moving slightly but progressively towards one side -- but that too could be offset (or exacerbated) by a natural tendency of the hand to rotate a bit.
From a practical point of view, see Geoff's post nr 109: