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Advanced sharpening and polishing techniques

post #1 of 14
Thread Starter 

Hello everyone, 

 

I would like to learn more about what's happening with a kitchen knife edge when you try to take it as far as possible with your equipment. During the past 9 months, I have been getting ever more familiar with my Konosuke HD2 gyuto and my sharpening kit (Bester 500, Beston 1200 and Arashiyama 6000) and I also started exchanging knives and sharpening tips with a friend of mine who owns a pair of Moritakas and a Tanaka gyuto. At one point I gave him my knife with the best edge I could put on it and he would would compare with his knives that he also sharpened to the best of his abilities, and then he gave me his knives and it was my turn to compare. This exchange continues. I am finding quite some differences between how sharp can a Konosuke HD2 be compared to Moritaka Blue 2 when sharpened by the same person. When we last did this, it appeared the Moritaka will take a sharper edge and will retain it longer as well, or that it will wear down more gradually and evenly.

 

Recently I have built asymmetry in my Konosuke (I would judge it 70:30) and polished the hell out of it with my Arashiyama 6k stone, followed by stropping with these pastes: http://www.highlandwoodworking.com/mediumfinestroppingpaste.aspx The included angle could be between 20° and 25° - I went thin.

The results were stunning, the knife was screaming sharp, more then ever before, it shaved my forearm effortlessly. Yet, the edge was not very durable, for instance after I chopped some herbs with it on a wooden board (rocking motion), the curvy part of the blade which gets the most pressure during rocking almost stopped shaving after just one cutting session. It went from "hairs are bursting into the air" to "I need to put pressure to produce any shaving effect at all". All that in 5 minutes of time. Would any of you have an idea what might have happened there?

 

When I retouched the edge with Ara 6k, the knife instantly started shaving again (although not as well as after the strop). The episode left me puzzled. 

 

My theory is that I had actually developed a wire edge by the strops that was good at shaving, but as soon as I went to the board, I have bent that wire and the knife lost its acute sharpness at once. Of course it still cut onions etc. with ease, but all lasers do. I couldn't see the wire or anything, I am only judging by the behaviour. My first thought then is to either stop polishing at 6k, forget about the strops and be content with it (the edge retention is better with stone-polishing only). But I like sharpening and getting to the bottom of things and I want to go further with my polish, so my second thought is to ditch the pastes and buy a yet finer stone (my hot tip is Gesshin 8k BDL used to praise over Naniwa Pure White which would be my second choice, anything else? Nubatama Bamboo?).

But maybe I made the angle too acute and it is not meant to hold? What could be the reasons behind the symptoms described? In the end, I would like the HD2 Konosuke retain its effortless-shaving sharpness even after some cutting has been done. 

 

From various comparisons with the Moritaka Blue 2 I almost started to believe there is a limit to where you can take the HD2: as if it was only able to get "scary sharp" for a very short time, then it would dull to non-shaving level, yet still "quite sharp + lasery properties" and then it would sit there for a very long time before it would take the next step and get dull proper. As if the HD2 was meant to be more *thin* than *sharp*, if you know what I mean. Whereas the thicker and heftier Moritaka had a more linear dulling curve in time: it would be super screaming sharp for quite some time, and then would dull and dull evenly without a flat time period of same perceived sharpness until, also, it would become just dull. 

 

I can't quite get my head around these characteristics and there is always the fact that I am no master sharpener and might have done many mistakes in both my technique, observations and conclusions. I would welcome a seasoned sharpener to shed some light and basically talk to me about what is happening in that micro-minute area of the cutting edge when it comes to different steels and different sharpening/polishing techniques.

 

Thanks a mill, 

Jiri


Edited by Machalik - 9/19/14 at 9:22am
post #2 of 14

You might be finding the limit on HD2.  Those angles are very acute.  You might try a microbevel on one side?

 

https://www.youtube.com/watch?v=xwnFrjiAA_8

post #3 of 14
post #4 of 14

Can we assume you are deburring in between grits and stropping?  That is something I do religiously.  Sign up for Murray Carter's news letter and you can watch sharpening videos (and I believe a 25% discount on a first order). 

 

If my knife isn't up to the three finger test I'll start at 1000 grit and again at 6000.  I feel for a consistent burr along the edge and swap sides and reduce number of strokes till it feels gone then deburr with cork, felt, or the pine board my stone sits on.  Then I strop on cardboard, deburr, then finish on newspaper and deburr again.  For establishing a new edge I go back to a Gesshin 400 and advance from there.

post #5 of 14
Thread Starter 

Hi gentlemen, 

Thanks for the insights! I thought of micro bevel as well, although I had hoped that HD2 could hold the very steep angle on its own. BDL once suggested he had sharpened his Kono HD2 to a similarly acute angle but his sharpening skills are way beyond mine so obviously when two people do the same thing, it's not always the same thing in the end after all. 

 

I do deburr between each two stones or grits. Since I was polishing the gyuto on Ara 6000 only (it was sharp enough not to need my 1200 stone and I don't own a 3000 grit stone, one that I am starting considering purchasing), I raised a tiny burr with it on the left side of the blade (= I was polishing the right side; I am right-handed), then took it down with the stone and raised it on the opposite side, a smaller one, and then I kept deburring on the stone until there was none. Then I used felt cube for final deburring, then moved to strops. Between each paste, I deburred on felt again, as well as after the last strop. This should not be a burr issue and I inspected the edge with my 60x magnifier an saw a clean edge. 

 

Since the knife is now once again polished with 6k stone but no strops, I will cut the same herbs (rosemary and sage) on Monday and see if I roll the edge again, as that's what I believe was what happened. If yes, I'll start experimenting with a more obtuse micro bevel. If not, then I will probably hold a wire edge puled by the strops responsible for the rapid blunting effect.

I'll update you on Monday/Tuesday when I am back at home. 

 

Thanks a mill!!

Jiri

 

PS: Since I gave this thread a rather universal (and lofty) name, I bid everyone who has questions or comments on a similar topic to come and post here as they like, this doesn't have to be a one man's problem thread. Thanks again!

post #6 of 14

What is your herb chopping technique?  Do you keep the tip down and rotate a rock chop?   Thatt's tough on the edge, but if you need your herbs minced then you need them minced.   It's not like you can roll up rosemary for chiffonade either, that's pretty much the only way to do it.

post #7 of 14
I would avoid "walking" though. No lateral forces on these edges please. I use a soft carbon with a flat section, holding it by the spine in the middle with my left hand, and the right one on the bolster. But my somewhat harder Misono carbon is flat enough for the same.
post #8 of 14

As already noted 20deg inclusive is very acute, and possibly only some of the newest super-alloys can tolerate any real board contact at those angles.  I believe blue #2 is going to be a bit better at edge-taking and holding compared to the HD's semi-stainless.

 

To put things in perspective, a sushi/sashimi chef will not even touch the board with the cutting edge, they use the tip to slice through the last attaching fibers.  They will use angles even more acute than 20 inclusive.

 

The most controlled pressure should be used along with some slicing motion to reduce the need for pressure.  Stropping on leather or rounding the edge of a fine Arkansas stone to be used as a steel (with the slightest of pressure) are the best methods of truing the edge.  The ark will also do some edge restoration and is much finer than your 6K.   Using the ark and gentler techniques I can maintain a reasonable 12deg edge on relatively soft steel for an adequate period.  Unless you are going to work like a fine fish slicer, perhaps 12deg is as acute as you should go.

 

Micro bevel works well, and will abrade away the final burr as well with an edge-leading stroke.  I actually micro-bevel the final angle when I put on a new edge.  Extremely light pressure, and a good 8k stone, I think you 6K might be a little to course to give a fine microbevel.

 

 

Rick

 

 

Rick

post #9 of 14
Quote:
Originally Posted by Rick Alan View Post
 

As already noted 20deg inclusive is very acute, and possibly only some of the newest super-alloys can tolerate any real board contact at those angles.  I believe blue #2 is going to be a bit better at edge-taking and holding compared to the HD's semi-stainless.

 

To put things in perspective, a sushi/sashimi chef will not even touch the board with the cutting edge, they use the tip to slice through the last attaching fibers.  They will use angles even more acute than 20 inclusive.

 

The most controlled pressure should be used along with some slicing motion to reduce the need for pressure.  Stropping on leather or rounding the edge of a fine Arkansas stone to be used as a steel (with the slightest of pressure) are the best methods of truing the edge.  The ark will also do some edge restoration and is much finer than your 6K.   Using the ark and gentler techniques I can maintain a reasonable 12deg edge on relatively soft steel for an adequate period.  Unless you are going to work like a fine fish slicer, perhaps 12deg is as acute as you should go.

 

Micro bevel works well, and will abrade away the final burr as well with an edge-leading stroke.  I actually micro-bevel the final angle when I put on a new edge.  Extremely light pressure, and a good 8k stone, I think you 6K might be a little to course to give a fine microbevel.

 

 

Rick

 

 

Rick

That's not entirely accurate... there are many times and cutting techniques where sushi chefs do come in contact with the board with more than just the tip.

post #10 of 14
Quote:
Originally Posted by JBroida View Post
 

That's not entirely accurate... there are many times and cutting techniques where sushi chefs do come in contact with the board with more than just the tip.

 

Ahahaha, I'm certainly not going to disagree with someone who has considerable professional experience here.  And I hate to have mislead any aspiring chefs in the particular area, as my sentence did imply "never" by not offering any conditional.  ;-)

 

Rick

post #11 of 14
Yeah.... I didn't mean to come across rude... Just trying to clear things up


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post #12 of 14
Thread Starter 

Thanks a mill for all the valuable advice, guys.

 

After having seen several questions regarding my herb chopping technique, I realised that might indeed be the culprit of the rapid dulling of the knife. What I of course did was put the knife flat over the herbs, then lifted its heel (= its belly must have dug into the relatively soft board) and then chopped the herbs with a rocking motion, the belly always planted firmly at the same spot but the heel was walking as if creating a punkah pattern. That, I can imagine, caused the belly to twist, roll and dull. Now thinking back about it, it seems as a stupid way to chop herbs as by principle it must be harsh on the edge. It was the belly that stopped shaving afterwards.

 

I have put what I think is an even more refined polish on the HD2 gyuto yesterday night and finished with a more obtuse micro bevel + stropping. Later today I will let you know how the knife behaves after a cutting session, although I am not convinced I want to use the same punkah-walking technique again. I probably will just for the sake of the test. 

 

Also, I discovered a very useful paper yesterday from Verhoeven that concerns razor edges, perhaps you have all read it already: 

 

https://www.wickededgeusa.com/files/knifeshexps.pdf

 

A lot of interesting info in it, especially when he talks about push vs. pull sharpening techniques and the measurable/observable differences in the bur it produces, as well as comments on stropping on clean leather and loaded leather. Very, very useful, I have yet to read it thoroughly.

 

Cheers,

J. 


Edited by Machalik - 9/22/14 at 9:44am
post #13 of 14

Some of the sharpening machine pictures made me cringe.

post #14 of 14
Thread Starter 

Agreed. I decided to skip all the machining-related parts and went on to Japanese water stones chapter directly :) 

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