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Thread: Gyuto and similar knife geometries.

  1. #1
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    Gyuto and similar knife geometries.

    I'm not sure if this is secret maker type info but I was wondering is there some visuals somewhere on what makes a knife made for a certain grind (50/50, 80/20 etc.) I'm familiar with the V shape and what I've seen on Jon's videos but maybe something isn't sinking in. My first thinking, with Gyuto, is that say a 50/50 would be about 50% metal on each side of the center line and 80/20 about the same.. 80%/20%? I know that sounds too simple but am I sorta on the right track ? And if that's so then a left handed would be opposite (20/80)? So then taking a 50/50 blade and making it say 80/20 would make it steer because of the larger amount of steel atop the 20 degree side making it shoot toward the 80 degree side ?

    I understand that there are other things affecting it like distal taper and (thin behind the edge) or 'wavy' like some or you get it.

    Yeah I may not have explained that all right but maybe someone could set me straight or at least get me not thinking about it

    Thanks

  2. #2
    Senior Member ThEoRy's Avatar
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    The whole 80/20, 70/30 thing really just refers to the way the edge itself is sharpened asymmetrically. It's not a 20 or an 80 degree side at all. Just a percentage used to describe the bevel height or which percentage of the total bevel (not angle) is on which side of the knife. If you look at both sides and they are the same height that's 50/50, if one side looks a little taller that's about 60/40 if it's a bit taller still 70/30 etc etc. Until you get to 99/1 which are honesuki or hankotsu knives or other knives that aren't a true single bevel with a hollow ground back. These knives have the majority of the bevel on the front side with just a tiny back bevel cut in. While true single bevel knives are 100/0 meaning the entirety of the bevel is on one side of the knife only. Since the back is hollow ground and laid flat on the stones, you aren't cutting in a bevel on the ura, merely deburring the blade basically.
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    Thanks, I follow you. I believe that the single bevel exists because of the ura and that set aside. I guess I'm looking for a bootcamp theory on why a blade is 80/20 or 70/30 besides 'that's how it's sharpened' I guess I keep seeing ppl describe geometry and I'm still looking for it. I have an old US carbon that I sharpened 70/30 and it seems fine. no real steering and good cutter. I just know I'm missing something.

  4. #4
    Dave recently posted a thread on this topic. If I can find it I'll link it here.

    ETA ~ Here it is:

    http://www.kitchenknifeforums.com/sh...-The-REAL-DEAL

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    Thanks figures it was there all along. I guess I've got my reading ahead of me

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    Charles ***[All statements I made here only my personal opinion and nothing more!]*** & Please bare with me for my crappy English!!

  7. #7
    its also possible for asymmetry to be a variation in angles on each side, but most often its a combination of angle changes and time/amount of grinding on each side

  8. #8
    Senior Member Benuser's Avatar
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    I sharpen my vintage French and Sheffield carbons slightly asymmetrical as well, and with me, they perform much better than with a strictly maintained symmetry. Is it because I'm used to it, my poor cutting or sharpening technique, or is it because of their inherent asymmetry?

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    I'm not sure the bevel matters as much as the grind on the blade face unless it's one of those large beveled ones (like a Yoshikane or Kochi etc). I've had enough time to experiment with various assymetries in bevels, but I can't feel the difference on most knives. The asymmetry of the grind seems to make a far larger impact.

  10. #10
    Quote Originally Posted by bkdc View Post
    I'm not sure the bevel matters as much as the grind on the blade face unless it's one of those large beveled ones (like a Yoshikane or Kochi etc). I've had enough time to experiment with various assymetries in bevels, but I can't feel the difference on most knives. The asymmetry of the grind seems to make a far larger impact.
    The bevel matters. Over the past year, I've been repeatedly sharpening my Global G-2, from what was originally, close to a 50/50, and slowly changing the bevels to more asymmetric bevels without thinning the blade above half a centimeter from the edge. The changes in resistance, initial wedging when cutting, and feel are noticeable.

    I had gotten the knife to a point where it cut really well, with something like the 70/30 or 80/20 shown here. But, in the same sharpening session, with what I considered to be very similar edges, a slight change in the bevels (again, I did not thin behind the edge), actually noticeably worsened the feel and performance of the knife.
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