# Thinning mirror polished knife



## GorillaGrunt (Feb 22, 2017)

So I've become "the knife guy" at work, sharpening for my coworkers and such. I've done my chef's Miyabi Artisan SG-2 8" gyuto a couple times; it seems that it's kind of thick behind the edge and the bevels are getting rather large in the sort of way that indicates that it would benefit from thinning. He has used this one for a couple years, sharpening mostly on Miyabi's Rollsharp I believe, and I've never seen a brand new one so I don't know exactly how much height has been ground away (although I just realized that I could take a caliper measurement and compare to the factory specs).

I can get the knife quite "technically" sharp on my stones, i.e. it will do the demonstrative tests such as shaving hair, shredding paper, and so on, but in terms of "functional" sharpness, i.e. performance vis-a-vis cutting food, it seems to require more effort than other knives that are equally sharp at the edge. Of course, I'm still not very experienced with J-knives, so I'm unable to quantify how far out of original spec the thickness behind the edge and the cutting performance are, and how far from optimal the original characteristics are.

This knife, which I've seen described as "blingy" on either this or another forum, has a tsuchime finish, a mirror polish on the upper and lower parts of the blade, a kasumi type band between the upper hammered shiny area and the shiny area immediately above the edge, and what appears to be an etched line where the cladding meets the core steel. It looks like this would be difficult to restore to original condition after any grinding on the face of the blade.

Unfortunately/fortunately, I am cursed/blessed with a powerful drive to optimize and refine and to ensure that I do things as correctly as possible in the best possible way. From what I've read about thinning and blade geometry, I see my options as the following:

-Continue to sharpen the edge bevels as they are. He gives me the knife to sharpen, I return it to him sharper. Pro: no risk of damaging or appearing to have damaged my boss's favorite tool. He seems pleased with my work on it so far. Con: I think it could cut better, and eventually it will cut noticeably worse.

-Thin it above the edge bevels and stop there. Pro: It will cut better, maybe even impressively so. Con: it will look, if not ugly per se, quite different from how it's "supposed" to. In its original form it is admittedly beautiful, although I prefer the simpler beauty of my Gengetsu, Hiromoto, or Sabatier.

-Thin it and restore the finish. Pro: better cutting performance, without diminishing the aesthetics. Doubly impressive. Con: I don't know how to do this. I'll have to figure out thinning first, which I'm working on with some cheap knives, intending to progress to my old 10" T-I Sab and maybe my MAC, and then polishing -- this thing is more reflective than any knife I've ever seen, so I wouldn't know what to use. 15k stone? 5000 grit automotive sandpaper? Polishing compound and a cloth? That's not even considering the four different finish types on this knife and the order in which to perform the operations.

So now that I've written this out, clearly in the short term option 1 is the safest - low risk and do exactly what Chef asks, option 2 is what I'd start with if it were my knife but is not viable for someone else's, and what I really want to do is option 3, despite the effort and learning required, because the term is knife knut and not knife knormal for a reason, amirite? :biggrin:

There's also option 1a: sharpen, do not thin, but ease the shoulders in a hamaguriba-esque sort of way for better cutting than an abrupt change in angle, if I understand the process accurately, and 3a: learn how to do all the tasks first, thin some knives, polish some metal and find a method to get it as shiny as a new Miyabi, and then offer to do it for other people.

What do you think? Any tips on thinning and restoring complicated finishes?


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## chinacats (Feb 22, 2017)

Knife needs to be thinned...easy to learn but probably best not to learn on the boss's knife. That said, it's a tool and not artwork...I think sharpening scratches give a knife character and performance is really what matters, right?


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## cheflivengood (Feb 22, 2017)

first tip is don't promise or practice on other people's money. Hand sanding is the best option for mirror finish and it will take you a very long time to do it well. pictures of the knife?


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## foody518 (Feb 22, 2017)

In the meantime of figuring out the thinning/mirror finishing/re-etching, you could try for cutting in a back-bevel of 5-8 dps with a coarse stone (going either all the way until the edge, or simply just shrinking the current primary bevel to a width you feel okay with), painter's tape covering the blade 1.5-2cm up from the edge just in case your angle drops for a stroke. 
Mmm actually, I just went and looked up photos. Could the middle part of this blade have a built in wide bevel thinning angle? Do you have any muddy stones?

My understanding of using a sandpaper or micromesh progression is that if you're going to mirror polished you will reduce the contrast of the 'damascus' pattern and it will need an acid etch to bring it back.


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## Jovidah (Feb 22, 2017)

First of all I'd put the choice up to him/her... There's more performance in the knive but achieving it might risk some cosmetic downgrade.
Second, foody518's advice of simply putting tape on most of the nice to protect the non-thinning areas is a sound one. I never bothered, and it shows.  
Third, I think just thinning it behind right behind the edge (essentially popping off the shoulders), isn't quite an invasive procedure. And if you simply take it through the whole progression of stones afterwards it can actually still look nice; simply keep going until all the scratches are gone and you have a mirror-ish finish.

But again; present the choice to the owner; it's their knife.


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## GorillaGrunt (Feb 22, 2017)

I don't have it now, next time he wants it sharpened I'll take some pictures and measurements. That's about the size of it: I know enough to see what ought to be done, but not enough yet to actually do it. On the plus side, now I have a better idea of what I want to learn to do with knives, and the particular things I need to practice; also, if I recommend that he have an expert work on it, then I still made a constructive suggestion.


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## GorillaGrunt (Feb 22, 2017)

Well, yes, I'd certainly ask what he wants done to it before doing anything; that just sounds like a good rule of thumb. I'm not sure about the built in thinning angle; that was actually one of my thoughts about the unpolished portion of the blade. I'll have to check with a straightedge next time.


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## unprofessional_chef (Feb 22, 2017)

Miyabi knives are already thin. If you make it any thinner the edge will be more prone to chipping.


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## natto (Feb 26, 2017)

This looks like you are running into a trap wide open, setup by yourself. Doing your chef a favor by spending your free time of a month or two, at the risk of harming your relation to him.

I did similar with results like shooting my foot.


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## fujiyama (Feb 26, 2017)

unprofessional_chef said:


> Miyabi knives are already thin. If you make it any thinner the edge will be more prone to chipping.



Once the knife looses enough steel and height over years of use (like in this case), it will need to be thinned.

Having experience with this knife I can say there's some sound advice in here. Again, it's a risky venture on someone else's knife. 

On the plus side these knives are pretty easy to thin because on the stone you can feel a secondary bevel. Thinning leaves the mirror finish in dull condition which will take an hour or two of sanding & polishing to bring back. There's no damascus to worry about re-etching and the hammering is hardly a concern (tape the blade flats off). The hamon on these is beautiful once thinned!


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## GorillaGrunt (Feb 27, 2017)

Thanks for the words of warning. Sometimes I get overexcited and want to charge ahead like Leeroy Jenkins. Sounds like there's definitely too much risk of damage to attempt this sort of thing on someone else's knife until I've gotten the process down, including the hiccups, hitches, slips, and goofs that might come up, not to mention having a better idea of how much time it takes before promising a time frame.

Personally, I care mostly about absolute performance since these are tools. However, one of my coworkers is also teaching himself to sharpen, and the front half of his blade is all scuffed to s__t. I don't know what he's doing, if maybe he's also trying to thin it in stages, but if I did that to one of my knives I'd probably be making an emergency run to the hardware store to get polishing supplies and spending some time fixing it before anyone else saw it, and if I did it to someone else's, I'd feel terrible and look like an idiot no matter how sharp the edge ended up. Notably, I've heard some variation on "so-and-so sharpened my knife and scratched the blade" much more often than dissatisfaction with the actual sharpness of the edge.

That said, having been brought back down to earth, I'll have to experiment with thinning and polishing on my own stuff, because I would like to be able to confidently offer to do this for other people. The relief bevel sounds like a good middle ground/stepping stone and one that I can practice on a few of mine.


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## foody518 (Feb 27, 2017)

Going off what @fujiyama said (as I don't own a Miyabi), if there's actually a secondary bevel that'll feel like a noticeable flat on the stones, that'll make the job easier


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## LucasFur (Mar 1, 2017)

1. If its a knife he has used for years then he got his looking good use out of it and now its a tool that he might like the look post thinning. 
2. tell him what your doing. 
3. when thinning, make sure to do the secondary bevel .. and the third bevel where the forge marks are to help with how thin it is. 
4. make sure you are able to give a good finish with a higher grit stone ,, and for super easy near mirror polishes just grab a dremmel and some polishing paste -- it will take a good couple hours potentially to bring back the mirror but it is possible, and R2 does not blow the temper that easy, just make sure your using bare hands to feel the steel. 
5. thinning the forged sections will firstly remove the peaks from the sides. -- thin your own knives first, just dont do a damascus unless you want to re-etch - or a kuruochi finish, unless you dont want kuruchi any more. mirror finish is probably the easiest to re-finish.


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## GorillaGrunt (Mar 14, 2017)

I ended up taking foody's suggestion and doing a relief bevel somewhere around 8 degrees. I confirmed my assessment of the knife noticing that the edge bevel was into the cladding at 15 degrees and about 0.7mm wide. Couldn't find my calipers or a factory spec for a new one, but I roughly measured the current height at the heel at 47mm. Thickness 0.5mm behind the edge was about 0.5mm, which sounds thick. The new bevel is over 1mm wide and ended up going all the way to the apex; I eased the shoulders and finished with a microbevel at about 30 degrees on both sides. The edge is holding up better than I had expected, and I advised Chef that he could get better cutting performance by having it thinned.

Now working on thinning and polishing some junky knives that I picked up for practice so I can eventually be able to do it for others.

Thanks!


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## GorillaGrunt (Apr 18, 2017)

Chef asked me to give it a shot anyway, so I did. I ground the wide bevel on a 220 until it was slightly less than half the thickness near the edge and the edge bevel looked "normal" instead of "too big". I forget the measurements, but it was something like from .032" down to .015". I smoothed it out with the 400 grit stone and tried to polish it with the 1000, but I didn't like the look of that finish so I gave the cladding a hairline-ish, semi-reflective finish with 400 grit paper and used higher grits on the core steel until a little contrast was evident. It's as close to the original appearance as I can get with the equipment I have (apparently what I need is a King 800) and cuts a lot better. There's a couple scratches from who knows what that I'll sand out next time I sharpen it, but it doesn't bother him the way it bothers me. Compared to most of the work on here it's amateurish, which is logical, but all involved are satisfied.

Thanks guys & gals, almost all I know I learned here!


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## RDalman (Apr 18, 2017)

Awesome that's a good read


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## foody518 (Apr 18, 2017)

Way to go for it  hopefully he appreciates the increased performance


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## natto (Apr 19, 2017)

Good result!


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