Thickness before putting sharp edge on chef knife?

A

AndrewC

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Nov 14, 2017
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Sure this has been asked before (yes, did a search! - this is particular to steel, HRC, and type of knife...)

Making chef knives for pro chefs and pro-am home cooks - 210mm gyutos and 180mm santokus. They're 80CrV2, HRC 60-61, according to my temper charts and a green HRC60 file from a decent Japanese mfg. I generally do symmetrical 17° edge-angle sharpening to K.I.S.S. Not quite sure what edge thickness I want to take 'em down to before putting a final edge on.

My concerns at that hardness are, I think, more about chipping and wear than edge roll? I'm shooting for a very hard/sharp blade with (modified) French geometry for push-slicing technique rather than rock-chopping. I have customers who're willing to maintain a hard, non-ss blade (bless 'em) - and learning to keep it sharp. So, if it's too fat behind the edge, they'll suffer trying to keep it sharp; too thin and it'll chip and have all kinds of other problems. Thoughts? Thanks!
 
Unless you are using for cutting things like bone (I am sure you are not), I have yet to find a practical limit to edge thickness that is too weak. I have done a number of nakiri and guyto in 1095 and 52100 at 62-64 HRC. Edge thickness at .002-.003 and have not had a problem with chipping. I tested a 1095 (at 62-63 HRC) Guyto blade (no handle) prior to sharpening by dropping it point first onto 1/2" steel plate from chest height (the blade was over length for my knife block and I needed to grind off 1/2" anyway). The blade was a FFG with a full distal taper. The final 1/8" or so of the tip snapped, but there was no damage otherwise (etched afterwords to see if there had been any fractures). It might have been worse if there had been a handle, but I figure that is more abuse than the blade would ever take slicing veggies.
 
Thanks - that's useful as kind of a worst-case, but I'm looking more for what thickness do I want to take the edge down to in my grind, before I sharpen it....
 
I suggest at least getting a bit below 0.01" before sharpening. Some would say below 0.005" or even less. (I think that was what Joe was trying to tell you)
 
I have been using S35VN and taking it down to approx. .005 and sharpening it at 15 degree per side. It is Rc60. I am going to try Nitro V at .003 behind the edge and sharpening it at 15*/side. It will be Rc64. We'll see what happens.
 
scott.livesey said:
close to zero as you can on edge, as important, shoot for 0.03 or less 1/2" above blade. for slicers, sharpen less than 10 per side
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Thanks, that's what I was meaning (I know I need near-zero at the edge... :-) My fault for not asking the right question. What I was looking for was "how far do I taper the blade, thickness-wise, near the edge, before putting the edge on?".
 
AndrewC said:
Thanks, that's what I was meaning (I know I need near-zero at the edge... :) My fault for not asking the right question. What I was looking for was "how far do I taper the blade, thickness-wise, near the edge, before putting the edge on?".
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Andrew I think the responses in this thread are telling you what they think are good thickness "at the edge"
I think you asked the question good enough but may not have understood the answers you were getting. Look over the responses again
 
If I may confuse things a little more how far behind the edge are you talking. I would assume approximately 1/8”-1/4” back?
 
I take calipers and measure as close to the edge as I can as I grind in my bevels. I generally take a kitchen knife down to less than .005 across the entire edge at 120 grit, then move up from there. I generally end at .002 or so by the time I am up to my finished grit. I don't worry about thickness farther up on most any kitchen knife as I don't use thick spines on kitchen slicers and I prefer FFGs. When constructed in this manner (or any knife with a spine thickness under 2mm and a bevel height of at least 1", your profile will be sufficiently thin to get a good cut as long as you take the edge down as described.
 
I am grinding an AEB-L suji right now and I took it down to like 8-12 thousands at 80 grit. Little thicker right at the heel.
 
So....

(A) NO: I was not asking how thick/thin to take it down to at the edge just before sharpening it. (Or at least, that wasn't what I needed to know. But thanks to all who answered that!) Because I worded the question poorly, that IS, though, what many/most thought I wanted advice on. My apologies!

(B) What I was looking for was, again, what Scott Livesey figured out, and gave me: on a FFG chef blade, how thin to take it down NEAR the edge - say at 1/2" from the edge all along the length of the edge from heel to tip -- so that you've still got enough beef left?

Here's the reason: if I were to take a FFG 210-240 chef/gyuto all the way down to damn near zero at the edge, depending on the thickness I started with and how wide the blade is from spine to edge at the heel, I may end up with not a hell of a lot of metal backing up the edge. (Especially when I've got a customer who, despite being in Michelin, has a heavy hand with his way-too-coarse bench stone, and he wonders where a few mm of his blade width went after a few months - once I learned what he was doing, we had a little come-to-Jesus about sharpening technique...!) So for a thinner gyuto, I may want to do a not-quite-FFG, down to a few thou at the edge, and a little more of a bevel when I put the edge on, no? I'm trying to trade-off what the thickness I need to leave, at a certain distance from the actual cutting edge, is, like Scott was saying.

(Dang, I think by explaining I'm actually complicating. Sorry. :-(
 
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