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Thinning a knife?

Sat May 25, 2013 12:57 pm

last week my father gave me he's knife ,a 22 years old knife and last nighet I sharpened it and it works good
but today someone said to me that if I want to make the knife cut even better I shuld thin the knife and I want to know if I should thin the knife or not?
and if I do need to thin the knife how do I do it? (its a european 50/50 convex graind knife)

Re: Thinning a knife?

Sat May 25, 2013 9:14 pm

Without knowing the brand, knife type, or even seeing a picture its hard to give you a proper answer.

Re: Thinning a knife?

Sun May 26, 2013 12:25 am

First put a good edge on it. Then let us know how it cuts for you. A picture of your knife would help us give you better answers.

Welcome to the Forum!


Re: Thinning a knife?

Sun May 26, 2013 12:27 am

Its no brand knife... because my father received it as a gift form a blacksmith and the knife type is french shef knife.
I will send later on the day a picture.

Re: Thinning a knife?

Sun May 26, 2013 8:00 am

pictures will be best specially if it's a custom knife like that.

Re: Thinning a knife?

Sun May 26, 2013 10:07 am

Thinning is another name for creating a compound bevel.

There are two ways to explain what thinning does... each a different face of the same coin. (1) Thinning prevents wedging. (2) Compound bevels maximize perceived sharpness AND durability.

Whether or not thinning will make a big difference in performance depends a great deal on the knife. As a rule, very thick and very thin knives (for instance, meat cleavers and lasers, respectively) benefit less than those somewhere in the middle. If your knife is somewhere in the middle, and there's nothing really out of the ordinary about its face grinds, An ordinary chef's knife is just that... ordinary.

The general rule for thinning European made chef's knives, is to thin at half the angle of the cutting edge. Thus, a typical 20* edge bevel (40* included angle) would require you to "thin" the knife by grinding each sides at a 10* angle until the grind almost or barely reaches the edge. As a practical matter, the Magic Marker Trick is very helpful for knowing when to keep going and when to stop.

Because you have to move so much metal to thin, you'll want to use a belt sander or a very coarse stone to begin. Those tools leave the thinned section so scuffed, you'll want to polish the scuff out to some extent. It's not absolutely necessary to polish the thinned section beyond around 1K (JIS), but it's not a bad idea either.

Good sharpeners often blend the shoulder of the thinned section (secondary bevel) into the face, so that it's not easily visible or felt. Similarly, they often blend the shoulder of the cutting bevel (primary) into the secondary. Blending on European knives is most easily accomplished with sanding pads. [Note that the use of the terms "primary" and "secondary bevel" are sometimes reversed; and that it's always a good idea to ensure you're on the same page as the person with whom you're conversing.]

Because fast, coarse tools can do so much harm so quickly, it's not a good idea to screw around with a knife you care about until you're sure of your skills -- particularly angle holding. When it comes to a full-on compound bevel (as opposed to a micro-bevel), whether you have the appropriate equipment and skills is a much bigger worry than if your knife is a good candidate for that type of edge.

In my experience, a micro-bevel style compound bevel often works as well as a full-on thinning. I've found that a good micro-bevel for European knives which see a lot of heavy duty use and subsequent steeling, is 25* over 15* *(FWIW, the angle set I use for my 12" ordinary carbon Sab chef's knife I use as a chef de chef and 10" stamped Victorinox cimiter). Assuming you use the "burr method" to sharpen, a micro-bevel on a knife made from the alloys most commonly used for European knives, should have the primary and secondary polished to the same 2 - 6K finish.

It's very easy to sharpen a micro-bevel. Just sharpen the secondary as you would an ordinary edge. Then, use a medium/coarse or medium stone with very light pressure to sharpen the primary; drawing a burr, chasing it, and deburring as usual. If desired, polish the primary on a medium/fine stone, with as little pressure as possible, trying not to draw a burr.

People typically fall in love with micro-bevels the first few times they use them. Just as often, after a few sharpening sessions, they find that the benefits aren't worth even the slight extra trouble.

Finally: Whether your knife will work better with a particular type of compound bevel or any bevel at all, depends on the knife's alloy, geometry, and how it's used.


Re: Thinning a knife?

Sun May 26, 2013 2:02 pm

Thank you boar_d_laze
I think I will try to micro-bevel the knife instead of thin it

Re: Thinning a knife?

Sun May 26, 2013 3:58 pm

I would agree with BDL in the sense that thinning a bevel is exactly as he described and his approach is good. Thinning the entire blade is yet another matter and what I suggested you hold off on doing. Approaching the matter by thinning the bevel is, as BDL suggests, a first - and in all likelihood a more than adequate solution.


Re: Thinning a knife?

Sun May 26, 2013 5:31 pm

Ken, one of several things I love about you is that there's one person in the universe who makes me appear practical.

Rich (BDL)

Re: Thinning a knife?

Sun May 26, 2013 9:08 pm

Practical is a good thing -- In my personal, non-professional, experience, it is worth my time to grind something like a Forshner 10" down to steeper angles because it gives me a knife that I can split hard squash or hack off fish heads with and not worry about, as well as being reasonably sharp for when friends come over and are going to work in our kitchen (the good Japanese knives get put away then that happens). I say "worth my time" because there is little cash investment (less than $30 for the knife) and not too much time, as the stamped blade is pretty thin to start with, so I'm not on the stones for hours reshaping the blade.

Once you put a good edge on it, if the knife cuts well for you, I'd stop there! You've got a knife with a huge sentimental value and it may be hard to improve significantly on its edge without drastically altering the blade. If you or someone else takes a belt sander or grinder to it, there is even the possibility that it may ruin the blade (getting it too hot, for example), damage it visibly, or create other problems, and you may not end up with a knife that is any "better" for you to use even if you succeed in regrinding it.
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