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TOPIC: *warning* deep discussion on microbevels

*warning* deep discussion on microbevels 5 months 5 days ago #14843

  • razoredgeknives
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OK guys... I recently thinned my first kitchen knife down to a zero grind and then put a microbevel (20* per side I think) on it... This thing is a slicing machine now. This was sparked after my question on the sushi knives and seeing how well they cut, so I decided to thin down my kitchenaide (or whatever the name brand is). So even though it slices well, it seems like the edge is denting /rolling after it contacts the cutting board a few times. When I try to put lateral force on the edge with my fingernail, I can visibly see it flex... So this got me thinking: how do the microbevels/grinds relate to edge strength?

For example... If I put a 2*/side full flat zero grind on the blade, and then put a .001" shoulder behind the edge with the edge finished at 20*/side, how does this differ and how will the durability differ from one that I have a FFG with a .040" thick edge at 15*/side with a 20*/side final micro bevel?

I hope you guys are getting my drift... How does the metal behind the edge affect durability even though the edge of the edge is finished the same (at 20*/side). I can't find any scientific or geometric research that reversals any knowledge on this point, but surely there is a mathematical way to determine the percentage of strength?
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*warning* deep discussion on microbevels 5 months 5 days ago #14849

  • zig
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If I'm understanding you correctly Josh, my first take is that the blade to metal ratio is just too thin and it won't hold no matter what.
The steel is not up to snuff.

Did you try it first without a micro bevel?

If you think of a straight razor and how thin it is, how much chopping can you do before it gives?

my 2 cents
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*warning* deep discussion on microbevels 5 months 4 days ago #14852

  • LeoBarr
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The quality of the steel is what it is all about if the blade is too thin then it will roll I rolled the blade on my shun santoku using it that've off strips of Serrano ham from the bone using the knife for something it was not designed for .
This is why a chef has different knives a boning knife is much thicker than a filleting knife .
Maybe you were a little over zealous with the thinning in this knife not to say it is unusable it will slice raw fillets or soft vegetables beautifully . I think you are on the right track further experimentation will help some times the thinning is only necessary to take the shoulders off the v grind if you can feel them when you pinch the blade edge I would thin them off the same can be done for a convex once again if the curve of the convex is really easy to feel it may again need thinning unless this curve is been used to remove meat from bone then the curve helps to stop the edge shaving the bone.
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*warning* deep discussion on microbevels 5 months 4 days ago #14854

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razoredgeknives wrote:
I hope you guys are getting my drift... How does the metal behind the edge affect durability even though the edge of the edge is finished the same (at 20*/side). I can't find any scientific or geometric research that reversals any knowledge on this point, but surely there is a mathematical way to determine the percentage of strength?

Interesting question! I'm afraid we'd need a metallurgist and a physicist to andwer this question in properly. Unfortunately I'm neither...

But on an inuitive level I'd say both Zig and Leo are right. The quality and hardness of the steel do matter.

And so does the thickness of the blade. Not only at the edge of the edge, but also (sometimes far) behind that. Imagine that you've thinned a blade such that it is only one micron thick at the edge and maybe a few microns behind the edge. If you now put a microbevel on this blade, it will still be a few microns thick at or just behind the edge. That could cause it to chip or roll.
Last Edit: 5 months 4 days ago by mark76.
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*warning* deep discussion on microbevels 5 months 4 days ago #14858

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LeoBarr wrote:
The quality of the steel is what it is all about if the blade is too thin then it will roll I rolled the blade on my shun santoku using it that've off strips of Serrano ham from the bone using the knife for something it was not designed for .
This is why a chef has different knives a boning knife is much thicker than a filleting knife .
Maybe you were a little over zealous with the thinning in this knife not to say it is unusable it will slice raw fillets or soft vegetables beautifully . I think you are on the right track further experimentation will help some times the thinning is only necessary to take the shoulders off the v grind if you can feel them when you pinch the blade edge I would thin them off the same can be done for a convex once again if the curve of the convex is really easy to feel it may again need thinning unless this curve is been used to remove meat from bone then the curve helps to stop the edge shaving the bone.

So apparently the thickness of the bevel behind the edge of the edge does matter.... What is ideal? Obviously not too thin, but nothing too thick either (I have heard .010 is ideal for most kitchen knives). So Japanese high rc knives can be thinner and still hold up I guess, whereas western knives won't?
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*warning* deep discussion on microbevels 5 months 4 days ago #14860

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razoredgeknives wrote:
So apparently the thickness of the bevel behind the edge of the edge does matter.... What is ideal? Obviously not too thin, but nothing too thick either (I have heard .010 is ideal for most kitchen knives). So Japanese high rc knives can be thinner and still hold up I guess, whereas western knives won't?

These lead to more questions from me. Hope not to confuse the issue.
Like what applies, if thickness behind an edge is the issue, to a hollow grind?
For example, isn't the edge angle thinner behind the relief and cutting edge?

I'm referencing Jay Fisher's page and image for info and food for thought, I hope Jay doesn't mind:

Ex1:


"Initial knife edge geometry
This graphic illustrates the initial geometry of a functional edge. Before an edge can be applied, the thickness of the blade must be relieved. The relief face is ground at a maximum of 20 degrees to the blade center line, and properly thins the metal behind the cutting edge. The relief face can be easily seen on the knife blade without magnification, and on knives with blade relief, this appears as a bright line of ground steel that may be 1/16" wide on a typical blade. Remember, the 20° is a maximum angle, and lower angles create a sharper edge and perform better, but are somewhat thinner in cross sectional area, thus affecting blade strength at the edge. "



"Hollow ground knife blade cutting edge geometry

More typical of the cutting edge on my knives is represented by the graphic shown here. Relief face angles are often 5-10 degrees, sometimes less, cutting edge face angles are 7 to 15 degrees. In order for low relief and edge angles to work, the blade grind must be significantly thin. This is where good grinding form, practice, and skill are demonstrated in handmade and custom knives. Factories and CNC machines can not grind blades that are thin at the edge. It takes a great deal of time, practice, and control, and can be dangerous for the inexperienced. Usually, factory knives are left thick, and are edged with one wide relief/edge face combination, which only allows a few sharpenings before the blade is too thick. Some makers and factories sharpen with a convex edge, which they sometimes call a rolled edge, because they roll the knife blade around while sharpening it. This is not a good edge because it is not clearly defined with accurate face angles, is thick and has high edge angles. and is not sharper no matter what you may read. The reason for a convex cutting edge is one of skill. It takes accuracy to create a cleanly beveled edge, and factories just round over the edges with power tools to quickly get the knife out the door."

Another thought I had was watching Sushi Chef's slice.
Is it me or do they slow down and seem to lessen the pressure on the board just before the cut is finished?, maybe saving the edge from rolling, unlike American/Euro style cutting and chopping.



Sorry for info overload and curveballs :)
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*warning* deep discussion on microbevels 5 months 4 days ago #14861

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I think the real answer is not absolute I would like to say it depends perhaps there is an ideal thinness relative to RC but the real answer is to thin it gradually over sharpenings rather than all in one go what will ultimately create a blade roll is hitting bones , cutting hard root vegetables and to a certain extent the way it is wielded so start thinning at the shoulders where it is possible overly thick and take less away as you approach the edge.
You can always thin it more another time if it is overly thin then some of the blade will have to be sacrificed to thicken it up.
I think feed back from the steel as it sharpens is probable an important factor if it sharpens very quickly then the steel is probable soft where as if it is slow to sharpen it is probable very much harder steel. This can only be gained over experience I think the further we go into sharpening the greater that feeling becomes this is not quantifiable in measurement be it thickness or hardness .
Even take two average chefs the likely hood is that the pressure and blade technique will differ from the other.
I am not sure that it is possible to be that scientific about it .
Perhaps someone else may be able to quote figures I would like you be interested to know .

Jon of JapaneseKnifeImports actually puts a micro micro bevel on top of the micro bevel so say his micro bevel is 15Ëš then he will do about 3 light passes with the finishing stone on one side at 25Ëš which strengthens the edge up (the side would be the right on a right hookers knife this can be done on a conventional "V" bevel).
Last Edit: 5 months 4 days ago by LeoBarr. Reason: additional point
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*warning* deep discussion on microbevels 5 months 4 days ago #14862

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zig wrote:
Remember, the 20° is a maximum angle, and lower angles create a sharper edge and perform better, but are somewhat thinner in cross sectional area, thus affecting blade strength at the edge. "

This is what I'm wondering about... How does the blade thinness affect the strength of the edge?

Those charts are very helpful, thanks ziggy!
Last Edit: 5 months 4 days ago by razoredgeknives.
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*warning* deep discussion on microbevels 5 months 4 days ago #14864

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That final bevel angle is still relative to the thickness and could be quite visible on a thick blade where as on a very thin blade two things happen the bevel is almost invisible and it is that easy to do that often it can be done with one or two of the finishing grits .
If the blade if overly thin for the steel then even a conservative bevel angle say of 20Ëš will still be delicate .
So I think I get back to my point in my last post .
If you have over thinned and the blade damages easily then it is a worthy lesson and perhaps for the benefit of all post a picture .
A comparison for me would be like riding a motorbike if you never come off you are probable not such a good rider and you do not know the limit of the bike.
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*warning* deep discussion on microbevels 5 months 4 days ago #14866

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LeoBarr wrote:
That final bevel angle is still relative to the thickness and could be quite visible on a thick blade where as on a very thin blade two things happen the bevel is almost invisible and it is that easy to do that often it can be done with one or two of the finishing grits .
If the blade if overly thin for the steel then even a conservative bevel angle say of 20Ëš will still be delicate .
So I think I get back to my point in my last post .
If you have over thinned and the blade damages easily then it is a worthy lesson and perhaps for the benefit of all post a picture .
A comparison for me would be like riding a motorbike if you never come off you are probable not such a good rider and you do not know the limit of the bike.

Good point Leo, a lot of this will be trial and error and see what works... I will try to get pics up soon
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