bevels, double bevels, angles.... I'm confused

Discussion in 'Cooking Knife Reviews' started by butzy, Dec 19, 2010.

  1. butzy

    butzy

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    Been reading a lot about sharpening on this forum, watched the video's of chefsknivestogo etc etc.

    But I'm now also confused.....

    I'm about to buy a carbon steel knife with a double bevel 70/30.

    I've also seen a couple of drawings (posted by BDL amongst others) of a double bevel and I wonder if these are actually the same things.

    I'm not sure if I am describing this right, but the double bevel according to the pictures looks like the knife has 2 even angles.

    The 70/30 double bevel sounds more like the edge of the knife is asymetrically sharpened (like the cutting part of the knife is slightly off-set to one side.

    Sorry if this sounds clumsy, I'm lacking the vocabulary to describe it properly...

    With the 70/30 bevel, what are the angles to sharpen at for a Japanese carbon knife (the Fujiwara KFH)

    15 degree on one side and 10 on the other side or so?

    Or am I totally wrong here?

    I'm only getting the knife in January (haven't ordered it yet) and am busy trying to get my sharpening up to scratch before I get it on an old stone I found (don't know the grit).

    First trying with some small knives to get the idea right and will then go on to an old Henckels carbon (looks like a meat knife or a petty). These should all be around 20 degree angles each side if I'm not mistaken, then later on to my globals (@15 degrees?)
     
  2. boar_d_laze

    boar_d_laze

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    It's confusing because different people use the same words to say different things.  Some people use "double bevel" to mean that the knife is sharpened on both sides -- which is also called a "V" edge.  While others, including me, use the term to mean that each side of the knife has two different angles.  For instance, a 15* cutting (primary) bevel sharpened over a 10* thinning (secondary) bevel. 

    Here's a picture of some edge geometries which are labled with the terms as I use them:

    [​IMG]

    It's worth reiterating that although this picture illustrates the most common use of "double bevel," it's not the only right way.  You just have to make sure you nail down the terms every time you have a discussion. 

    I know.  Annoying.

    To make things even more confusing -- especially for someone who isn't a native English speaker -- sometimes the terms primary and secondary are used opposite to the way which I just described.

    Since you're more or less just embarking on freehand sharpening, you probably don't want to sharpen a double bevel.  It's actually pretty simple to lay in what's called a "micro bevel;" in general, double bevels make for a very nice, durable edge; but at this stage of the game it's a complication you don't need.  Once you can draw a burr and deburr, we'll talk more about it if you like. 

    BDL
     
  3. chrislehrer

    chrislehrer

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    Basically this isn't something you need to worry about very much. What you do is, you lay the knife on the stone and lift up on the spine, tilting the blade, until the edge just barely bites down on the stone. This is the easiest way to match an existing angle. Then you maintain that angle while you grind. The only reason to worry about angles beyond this is if you want to change something, which means a good deal of work (though it is usually effort worth the time) or because you're curious.

    I generally use the term "single-bevel' to mean what BDL calls a "chisel edge"; I don't like that term for reasons irrelevant here. It means that at least right down by the edge itself, the blade has one angled bevel and one that is straight up-and-down. This is a very abnormal way to sharpen a Western knife, and not a good idea on the whole.

    Everything else is basically double-beveled, and you can use BDL's chart to give you some idea of the possibilities. Asymmetry doesn't change anything: double-beveled simply means it's not chisel-edged.
     
  4. butzy

    butzy

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    Since pictures say so much more than words.....

    Can someone tell me where to find a picture of a this 70/30 double bevel of the Fujiwara?

    To me it looks like it is a V-edge (if I go by the drawing above) of which both sides are sharpened at a different angle. Now what would those angles be?

    I'm just a very curious person!!!!

    Thanks Chris for explaining how to find the right angle! That will definitely work in practise.

    I always work better if I know the theory behind things as well. It sort of makes me understand what I'm doing instead of just doing it (look at it as a character flaw /img/vbsmilies/smilies/rollsmile.gif
     
  5. phaedrus

    phaedrus

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    Here are a few pics.  The first is from the ZKnives blog.  The closest to the Fujiwara is going to be the 4th one from the left.

    [​IMG]

    Here's a smaller picture, but it's more like the actual geometry of the knife you're talking about.

    Please excuse my crappy Paint job.

    [​IMG]

    Ration can be confusing; it has nothing really to do with angles but rather how much of the cutting edge is on each side of the centerline of a line that bisects the knife vertically..  In my crummy pic there's a red line dividing the blade into two halves, left and right.  70/30 just means that 70% of the bevel is on one side of the line and 30% is on the other.  The little yellow mark is meant to show the angle of each side.  Now note that depending on the other dimensions of the blade, each side could have the same angle, or each a different one.  But angle isn't really related to ratio.  I hope I'm stating this clearly.  You can change either angle a bit but maintain the ratio so long as you adjust the thickness of the blade.

    [​IMG]
     
    Last edited: Dec 20, 2010
  6. phaedrus

    phaedrus

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    Last edited: Dec 20, 2010
  7. chrisbelgium

    chrisbelgium

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    Here's a real situation that may help a little more. Many Japanese knives are delivered just a little sharpened on one side and a minimal deburring on the opposite side.

    The picture on the left shows how this carbon knife came. You can clearly see it's almost 100/0, but was probably 99/1. This is factory sharpening on just one side which is called single bevel.

    Let's simply agree for clarity that a double bevel is sharpening on both sides. A V-edge is a double bevel with a 50/50 repartition and even less seen in Japanese knives than an albino rhino.

    Don't worry about the numbers 70/30, 80/20 or 99/1, they are no less than estimated values.

    The other 2 pictures are somewhat irrelevant for you right now. Let me add perhaps that this knife was "thinned", which means that the part that I marked with A and B has been grinded away. In this stage it's still single bevel sharpening, but, at a very low angle. Normally you would go to a 15° angle for Japanese knives. The moment you start to grind on the other side, it's turning into a double bevel.

    Let me also add that you will always end up with slightly convexed bevels. Simply because noone can ever hold a knife that fermly -while making sharpening movements- to get a 100% flat surface.

    [​IMG]
     
    Last edited: Dec 20, 2010
  8. phaedrus

    phaedrus

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    Nice pics!  Better detail than anything I could find.
     
  9. chrisbelgium

    chrisbelgium

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    Now, on the angles to produce. Many people will tell they sharpen at 15° or 10° or whatever. The very thruth is they have no clue at all! Not that it matters that much. Later on, when you have acquired some experience, you will automatically go to an angle that suits you best naturally, even without knowing the exact angle. I strongly suggest to keep that angle and none other. Consistency in sharpening is the key-factor for success!

    Anyway, I made this little chart a while ago, it has been posted on KF and FF too. A very simple thing to find out exactly at what angle you are sharpening at, or to adjust the angle for any particular knife. All knifes are all different. It's a good thing for sharpening novices to check how good you are at estimating sharpening angles.

    How does it work?

    Measure the height of your knife from the heel to the spine. Let's say a 240 mm knife you measure has 50 mm height at the heel. Look 50mm up in the left column. Now, follow the row to the right untill you reach the place where the top of the column appears 15°; you will find 12,9 mm. This is the distance the spine of your knife should be above the stones.

    You may have to click on the image to see it full size. Please feel free to download and print it. It's quite helpful.

    [​IMG]
     
    Last edited: Dec 20, 2010
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  10. butzy

    butzy

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    Thanks all, think I'm beginning to understand it.....

    The pictures are especially helpful!!!

    As far as angles are concerned,

    What I'm doing at the moment is making the angle I'm intending to use out of cardboard so I can easily check it.

    Definitely need to work on the method Phaedrus describes and learn to feel the right angle.

    This hasn't been possible with the knife I've just been working on as it had no angles and no sharpness left to deal with. Used a 20 degree angle on an arbitrary sharpening stone (doesn't have a brand name or grit on it) and managed to get it sharp.

    But not sharp enough yet!

    We'll keep on trying......
     
  11. phaedrus

    phaedrus

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    A cardboard angle gauge can really help- use it if you like it.  Sometimes I use a special device (aka "The Gizmo") like a Pana-Vise to hold the stone at an angle so I can simply sharpen horizontally.  Some people cut a block of wood for this; for example, you can make a wedge with a 15 degree angle and that's about ideal for many kitchen knives.  I also use an Edge Pro Professional model with a ton of custom stones.  And sometimes I find it enjoyable to sharpen freehand on stones, especially if I just have one or two to do and don't want to drag out all the stuff.  Plus I have some nice stones that aren't available for the EP.  Everyone has different methods but I really like soft stones because you can really feel the difference when a knife is digging in (too steep), skating over the top (too shallow) or biting right on the edge.  Soft stones refine your technique IMO. 

    You make one excellent point, Butzy- sometimes there is no real bevel to follow.  If a knife's edge is very worn you'll often just have to pick and arbitrary angle and have at it.  I do this all the time.

    Lastly, don't get discouraged if it takes awhile to learn.  In my case using many different techniques and tools really helped as they all reinforced each other.  Years of freehand sharpening really helped my technique on the Edge Pro, and being able to watch a burr being created stroke by stroke on the EP helped me achieve a higher level of understanding of the actual process of sharpening.  And both were helpful in making the leap to powered gear like my belt sander.  One nice thing is that nowadays there's a lot of good info out there; you might want to check out Dave Martell's videos on YouTube.  Mark Richmond has several sharpening videos geared for novice sharpeners on his site, ChefKnivesToGo.