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 Post subject: Does an asymetric edge matter for lefties?
PostPosted: Sun May 12, 2013 1:02 am 
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I am interested in a Masamoto VG. You don’t mention it on your website, but it is my understanding that they have a right-handed 70/30 bevel. How hard would it be for an intermediate sharpener who is left handed to change the bevel? Not even shure at this point which side the 70 is on and which side the 30 is on. Would that be obvious. Thanks.

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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Sun May 12, 2013 1:03 am 
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The bevel on the edge won't matter to your use of it. You can sharpen it evenly and you will eventually even it out if you like.

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Mark Richmond
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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Sun May 12, 2013 1:04 am 
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Wouldn’t it be better to reverse the bevel? They must have a reason to make it that way for right handers.



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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Sun May 12, 2013 1:06 am 
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Theoretically yes but in the real world you can't tell the difference when you cut with the knife if the edge is asymmetric or not. They do the edge this way to increase the cutting performance of the knife slightly. I've had this question a thousand times and it frightens lefties but I'm telling you if you blind fold yourself and cut with an edge that is asymmetric on the left or right side you won't be able to tell the difference at all. (don't try it blindfolded).



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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Sun May 12, 2013 2:54 am 
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There's a difference of opinion on this. What I'm going to write about might seem like disagreement, but as far as I'm concerned Mark's right and I'm going to bring up some nuances which may or may not be important depending on your level of skills as knife user and knife sharpener, and depending on a few other circumstances.


What is asymmetry?
Let's start with some definitions.

For our purposes the right side of the knife is the right side when the handle is pointed toward the user and the edge is pointed down. Left side, of course, vice versa.

Right handed asymmetry is accomplished by sharpening the bevel on the right side of a "V" edge so that it's wider than the left. The "ratio of asymmetry" numbers are a function of the difference of bevel widths. There are a couple of ways to express this. The clearest is as a simple ratio, like 2:1. A blade with 2:1 right handed asymmetry has its right side bevel twice as wide as the left.

The other way, somewhat less intuitive but more commonly used is as a fractional quotient. A blade which is 90/10 righty, has the right side bevel nine times as wide as the left. This method is somewhat more difficult to use when the ratios don't come out so evenly; for instance, 60/40 (6:4) or 70/30 (7:3).

Don't be tricked by published asymmetry numbers or by some of the talk you see in the knife forums. Ratios of asymmetry are almost never exact. Without very sophisticated measuring tools even professional sharpeners can't accomplish perfect ratios. The usual measuring device for professional and home sharpeners alike is the US GI Mk IV Eyeball. Thus, 70/30 and 60/40 are so close that they might be confused for one another. I usually think of them as 2:1 and sharpen accordingly.

What does asymmetry do?
An asymmetric knife will tend to steer straight in the hands of a correct-handed user, but steer and/or torque away from the wide bevel in the hands of a wrong handed user. The more asymmetry, the tighter the grip, the more it will tend to steer.

Everything else being equal, a more asymmetric edge will have more "perceived" sharpness than a less asymmetric edge, because the edge itself is thinner up to the point where the shoulder of the bevel of the off-side meets the face.

However, everything else being equal a more asymmetric edge will not be as durable -- especially when it comes to resisting bending burrs caused by impact.

Knives which are very thin, lasers for instance, tend to benefit less from asymmetry than knives which are somewhat thicker; but it still makes a difference. The sharpest knives I've ever used were highly asymmetric lasers.

What should you do?
Sharpening almost always represent some degree of compromise between sharpness and durability.

Harder, stronger knives can hold more asymmetry than softer, tougher knives and still stay less susceptible to impact burring; and more asymmetric knives seem sharper. So it seems reasonable that you should sharpen your knife to the highest ratio of asymmetry it can handle.

However, if you live in a household which includes both right and left-handed users, you have another area which requires some degree of compromise.

I'm left handed. For years I sharpened my knives 2:1 right so that my wife would enjoy the benefit of correct handed asymmetry. That level of asymmetry wasn't a problem for me, partly because it's so mild, and partly because I use such a soft grip. That level of asymmetry wasn't a problem for the knives either, and they were all fairly soft, tough Euros.

Western sharpeners shaped their edges to 50/50 symmetry since forever. And somehow, everyone still managed to cut onions. So... don't lose your perspective and get nuts about asymmetry.

For a great many, normal, V edged knives the 60/40 - 2:1 - 70/30 range is an ideal compromise. Now that my wife and I have our own sets, I sharpen mine to left handed asymmetry. She still uses my knives sometimes. Because she uses a naive grip, they fight her. And because I'm not quite as dumb as I look, it's not something I point out.

How do you sharpen asymmetry?
Simply by grinding one face more than another.

As a practical matter, if you use the "burr method" of sharpening, and always sharpen the first burr on the outside face (left side if you are left handed, right side if you're a righty), your knife will eventually develop something close to 2:1 without a lot of adjustment.

You don't want to take more metal from the knife than you have to, but you do want a knife which works for you. If you're a lefty and buy a right handed knife which fights you, profile it to 50/50 as soon as you realize the problem. After that, just start and finish your sharpening sessions on the left face of your knife, and you'll get to 2:1 soon enough.

An even better way, if you buy from a retailer which provides good sharpening services (like CKtG) is to have the knife profiled by a professional sharpener. It's not a big deal.

What about angles?
There's some disagreement about this.

Some people suggest sharpening the different sides at different angles which (sort of) complement the ratio of asymmetry. For instance Dave Martell might sharpen an 80/20 right handed knife with a 10* bevel on the right side and a 30* bevel on the left. Dave argues that if the angles do not reflect the asymmetry the knife will tend to steer.

I disagree with Dave and sharpen both sides to the same bevel angle. Most factories which ship asymmetric edges, also sharpen both sides to the same bevel angle. But it is not unanimous. I'm not sure how the pros who post here sharpen. I suspect that most use equal angles on both sides.

Other questions?
Ask.

BDL


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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Sun May 12, 2013 3:34 am 

Joined: Thu Jan 03, 2013 3:09 am
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Lets face it, all of us on this forum are pretty anal about getting the perfect knife with the perfect edge. If Masamoto sharpens 70/30 for right handers then I want a 30/70 for a left hander. There are a number of suppliers that will change the bevel for a left hander for an extra charge. If we are going to buy $200+ knives we want them just the way the manufacturer intended. It's easy to blow this off and say it really doesn't make any difference, but I don't believe it. It probably doesn't make any practical difference that anyone would notice (so Mark is right), but that is not really the point is it.


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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Sun May 12, 2013 6:01 am 

Joined: Wed Apr 25, 2012 10:29 am
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Location: Philippines
BDL is a lefty. I too am a lefty.

I don't really get bothered too much with righty knives except when it's single bevel. 30/70 righty is the max for me. beyond that i get steering issues.

I got a few righty knives. Most of my chef knives are righty. I'm in the process of ever so slowly converting them to lefty. why I am taking it slow? i wouldn't wanna waste the metal away too much to get it to how i want it as soon as possible. since it doesn't bother me, i'll just sharpen away what i need til it becomes completely lefty. all the knives i buy will become lefty so, whatever i buy, i make sure that they'll stay with me a long long time. gotta make the right choices for knives if you do it my way.

everyone does things how they want them so, do things at your own pace.


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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Sun May 12, 2013 4:05 pm 

Joined: Thu Jan 03, 2013 3:09 am
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Just to add to the confusion here is what Masamoto says in regard to this question with their VG knives.

For sharpening Double bevel edge 30/70 edge (the knife is left handed version edge), we recommend the sharpening angle approxiamte 12’ for sharpening left sider of blade edge, we recommend the sharpening angle approxiamte 15’ for sharpening opposite side of blade edge. We recommend you to sharpen the left side of blade edge more than right side blade edge. If total sharpening stokes are considered as 100%, you sharpen left side of blade edge for 70%, you sharpen right side of blade edge for 30%. These sharpening instructions are recommended for keeping the original edge shape.


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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Mon May 13, 2013 3:16 pm 
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Masamoto's advice isn't much different than mine. Except:

  • If you can accurately freehand sharpen a 15* bevel on one side, and a 12* on the other, more power to you;
  • If you can feel the difference in use between equal bevel angles and slightly different bevel angles, ditto; and
  • Counting strokes sucks as a method. Better to learn to feel and see what you're doing and adjust accordingly. Eyeballing asymmetry is bad enough. Hoping you get it right simply by counting strokes is beyond optimism.

BDL


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 Post subject: Re: Does an asymetric edge matter for lefties?
PostPosted: Thu May 16, 2013 12:01 pm 
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I'm a confused mix of right and left handed in a task specific sort of way. Sometimes I dice food, cutting rows righty and columns lefty :)

BDL, you saved me a LOT of writing. Brilliantly clear posting. Only one minor point of disagreement. Saying that Dave might sharpen at one angle on the right and another angle on the left presupposes that he actually measures angles :) He really has no idea what angles he uses and his explanations of sharpening angles on asymmetric blades defy any logic. His rants on the subject are best simply ignored. So yes I completely agree with your explanation of this consistently obscured topic. I don't change angles on the two sides, just the amount ground on each side. And if one wishes to also make a more acute edge on both sides and preserve the asymmetry ratio, the explanations for how to change these angles on the two sides becomes hopelessly confused, exposing the utter nonsensical discussion of determining how to set two different angles on an asymmetric edge. Just go back to basics - compare the size of the right bevel to the left bevel as a ratio.

So let's go on from here. Ignoring traditional single bevel knives for another topic, let's talk about double bevel Japanese knives. Many Japanese knives are made asymmetric - and ideally you want the edge to mimic or mirror the ratio of the knife's asymmetry. This let's the knife come straight down on the edge and it gives you a neutral steering knife. If you are lefty, you COULD reverse the edge asymmetry to a left bias, but you are still stuck with a biased blade asymmetry. This is what is typically done to 'convert a knife' to a lefty knife. Personally I would simply suggest converting to a 50/50 grind as a most reasonable and versatile compromise. For a lefty, making a double bevel knife with a lefty bias and a matching grind might be ideal, but this might be pretty rare. I do know of a left handed Japanese knifemaker (Nubatama) and could inquire further about this point.

Another related point is the handle. Many handles are symmetric. No problem. Some are 'D' shaped handles. I find a right handed 'D' shape a bit awkward in my left hand. With a loose grip, it can be ignored, but for dedicated use lefty, get a neutral or left handed handle.

So let's get to the practical aspects of this discussion. If the knife cuts straight in your hands, leave it alone and don't screw with it. If it pulls too much in one direction or another adjust this out by altering the edge asymmetry by grinding more on one side of the blade or the other. A good test is cutting a melon in half. If you can cut straight down without it arcing or pulling you are good to go. Cutting green onions or small diameter objects - doesn't matter.

If this sounds like adjusting the wheel alignment on a car, then you understand the issue quite well.

If you want to see a video about this click here :)





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Ken



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