Any tricks for sharpening SG2/R2? Having trouble

[miggus]

Hi guys,

so I went for the shiny stainless promises of Yu Kurosaki and liked his knife quite a bit. Now that they're due for a sharpening session, I have encountered a lot of problems. I can't get them sharp for the love of it. Actually, they went duller since I have started to work on them lol.

My sharpening skills: Certainly nothing to write home about, I'm lazy and don't do fancy paper cutting optimizations and such things. But I have been sharpening my own knives for a year, usually I get them to a point where they will cut paper, although with a bit of drag, no perfect push-cutting. I usually start on a bester 1200, raise a burr on both sides, deburr, do a quick refining on a Rika 5k or on the newly acquired Belgian Blue. I have never stropped.

My own knives until this point were all carbon, but I also sharpen the usual standard issue stainless for friends and family, and get those sharp as well. I take even less care with those, usually I take those straight to the 220 pink brick or the SG 500 and then just do a tiny bit of refining on a 1000 grit.

That is normally enough to get very workable edges that last a fair while. But not with the SG2 - I removed a lot of metal actually, but the knife still is super dull. I also got weirdly feeling burrs, it took a long time to get them even on the SG500 and they felt duller and fatter than on carbon.

I get that it is mainly a practice thing, but any advice would be welcome. I'm a bit puzzled since SG2 is supposed to be fairly easy to sharpen, even though I did some research and read that it can give people trouble.

 

[gc0220]

I think it's your technique. R2 steel in my experience sharpens up quite nicely and quite easily. It's not like it's carbon steel but it's not bad to sharpen at all. A moderate step above another stainless steel like vg10 at 61 rc and nothing like hap40 tool steel at 65 rc, which in my experience is by far the worst steel used in Japanese kitchen knives to sharpen. Anyhow, Something like a shapton glass at 500 grit would make very quick work of it. A 2000 grit shapton pro, much less aggressive cutting than the glass stones at the same grit much less lower grits, is the most course I ever needed to use, even after doing a cutting test on an R2 knife with a thicker grind that had the edge badly dulled. And it didn't take long at all. It was very easy to get it screaming, sticky edge, sharp again. In fact I can easily touch up slightly dulled R2 on even something like a shapton pro 8k or higher. Not an issue and doesn't take much effort or time.

Here's what I'd suggest. Use firm pressure and stropping strokes only for now. Just try it to get your method down, then you can go ham. Start at either the tip or the heel, make contact with the stone, and pull the knife back over the stone, following it's natural curvature in one long swooping stropping stroke. Do that with firm pressure a few times, checking the edge, then when it's ready flip it over and do the other side. Once you get that down, as far as the pressure and following the natural curvature of the blade on the stone, you can use smaller strokes to focus on sections of the blade at a time, probably next time cuz you'll be done sharpening for now.

 

[miggus]

Dear Doctor @gc0220,
you prescribed exactly the right medicine

I tried it right away and the results are already much better. Thanks a lot!

 

[miggus]

I wonder whether the R2 Nakiri will, with the right technique, get as bitingly sharp as the Moritaka AS. The latter gets just so nicely aggressive with a super grabby edge with very little effort.

Theoretically, R2 should be capable of a very similar edge quality, right? We'll see if I can get this to happen.

 

[gc0220]

I'm glad that helped you.

Absolutely. R2 takes an excellent edge, for practical considerations on par with AS, and thanks to it's vastly superior abrasion resistance it holds said edge considerably longer than AS. Especially when cutting on something like a wood board. However also thanks to that abrasion resistance actually getting R2 hair whittling likewise takes quite a bit more work and effort than AS, which like all those carbon steels is just so easy to sharpen. In my experience R2 is not "difficult" to sharpen though. Some steels seem to just want to get super sharp and other you have to really fight with to get there. R2 wants to get sharp. And when I say sharp, I'm talking HHT, catching and cutting free hanging hairs, sharp.

A thing to consider is that there is going to be more variation in hardening targets for AS compared to R2. Personally, I find I tend to enjoy harder knives more in the kitchen, and especially when you're talking about the no and low alloy stuff like AS. No amount of hardness is going to makeup for the difference in abrasion resistance between these two steels though. Practically speaking It's just a tradeoff between how quickly it goes dull vs how much effort it takes to get sharp. Good AS like a morikata is a fanstic thing, very pleasurable kind of knife to use. As for R2, I can understand why it's so common and quickly become the new "standard" in premium Japanese kitchen knives in a way. It's as hard as all but the very best carbon steels, it doesn't rust, it readily takes screaming edges, isn't hard to sharpen, and the edge retention is for sure a noticeable step up from say vg10.

I'd suggest for now just sharpening on a 1k or 2k, ideally something like SG but a SP or chosera works fine, if using the chosera I'd go 1k or 800. You should be able to shave hair at the skin or slice through a free hanging paper towel at this point, but if you're just learning consider that a goal rather than requirement. Personally, I usually finish it on an 8k SG, then strops, but you can skip that step as it took some time for me to get skilled enough to where I was actually getting the blade sharper rather than duller once I went to a finishing stone, basically anything over 5k. Get some diamond or cbn, say 1 micron, and try it on something like basla wood. These are just suggestions obviously. A variety of different things will work and also personal preferences vary. Give it a good refining, that's going to take *at least* half a dozen good strops on each side, then alternating, and you'll be good.

 

[miggus]

Thank you for taking the time! That is a lot of very good information right here.

It's just a tradeoff between how quickly it goes dull vs how much effort it takes to get sharp

Yeah, that sounds logical. Stuff that is more abrasion resistant in cutting will resist abrasion more in sharpening. And corrosion will accelerate dulling obiously in non-stainless steels.

1k or 2k, ideally something like SG but a SP or chosera works fine, if using the chosera I'd go 1k or 800.

Hm, I got a Bester 1200 - if I see it right, it is roughly comparable to those stones and fine for R2 as well, right?

Personally, I usually finish it on an 8k SG

Sounds great! I think I'm also at the point where I don't really improve the blade with such fine grits. I assume that the Rika 5k and Belgian Blue will be fine enough for me at the moment, until I'm a lot better.

Get some diamond or cbn, say 1 micron

will do

 

[Nemo]

A couple of common issues with SG2 :

1) Incomplete deburring.

This is the big one for me. There a number of interesting threads on deburring that you would do well to peruse. It's also worth looking at the @Kippington deburring technique (search for "Kippington deburring video"), as this works very well with SG2. Indeed, it was my standard deburring approach to SG2 until I obtained a diamond finishing stone.

On that note,


2) carbide fall out/ pull out.

SG2 has a decent volume of hard carbides. If you sharpen it at too acute an angle with a stone whose abrasive is softer than the carbides (basically anything other than diamond or CBN), you will abrade the steel around the carbides, but not the carbides themselves. This theorectically leaves the carbides standing proud (and not very sharp) or unsupported, so they are torn out of the steel matrix (and the craters left behind are not very sharp). This only occurs at acute edge angles. The higher the carbide volume, the less acute an edge will be supported. This is why the Kippington deburring method works well- it leaves behind a well deburred microbevel which is in effect a much less acute edge angle.

Note that carbide pull-out is (at least theoretically, but this also fits with my experience), mainly an issue with fine stones. Coarse abrasives generally can't get between the carbides and there is evidence that they will abrade hard carbides. My experience is that it is also less of an issue with diamond abrasives.


My current approach is to sharpen SG2 on a 1k AlOx stone, then polishing the edge with a 3 or 6K diamond stone. With careful deburring, this produces very sharp edges. Did I metion the need for careful deburring? I suspect that the fine diamond stone abrades any proud carbides. I wonder whether steels with even higher carbide volumes need diamonds at the 1k level.

As mentioned, I used to use the Kippington deburring method for SG2 and I still do when I don't have access to a diamond stone.

A third alternative is to sharpen at a less acute angle (or leave a microbevel) while paying close attention to deburring (which is what I did before seeing the Kippington deburring method).

 

[miggus]

Thanks @Nemo, I'll be looking into SG2 deburring and the Kippington method. And try to get around the diamond stones for now

 

[gc0220]

Great point about dealing with burrs, especially if you're going to do any significant grinding at a grit like 1000, particularly with edge trailing methods, you're gonna get some burr action big time. I didn't even mention how to deal with that if it comes up. For sure you want to minimize it on the stone before moving on to anything else, even using another method to pull it off, then touch it up and move on with the process. Just alternating strokes with increasingly light pressure is usually enough to break it down on the stone, but you can also take it pull the blade through some wood or whatever to get rid of it, then touch the edge up and continue.

Another thing that slipped my mind was asking what sort of knife profile he was working with, as it would have been relevant to know and adjust the advice and whatnot. I was imagining a gyoto for some reason.

As far as carbide tear out. Interesting. How do you detect or know when such a thing is happening on a practical level? Basically, how can I know when it's happens? If it does happen, the solution is to use a harder abrasive capable of directly abrading various carbides. Alumina isn't capable of abrading say vanadium carbides directly, but diamond is. It's apparently less relevant or not relevant at sharpening grits like 1000, but it becomes relevant at polishing grits of say 5000. Do I have that right?

I'm probably forgetting a few things, but that's all I got for now.

 

[Nemo]

As far as carbide tear out. Interesting. How do you detect or know when such a thing is happening on a practical level? Basically, how can I know when it's happens? If it does happen, the solution is to use a harder abrasive capable of directly abrading various carbides. Alumina isn't capable of abrading say vanadium carbides directly, but diamond is. It's apparently less relevant or not relevant at sharpening grits like 1000, but it becomes relevant at polishing grits of say 5000. Do I have that right?

I guess carbide pull out is a potential issue if you can't get the knife very sharp despite thorough burr control and deburring. In this case, I'd try a less acute angle or a microbevel.

The guy over at Science Of Sharp showed that coarse AlOx will abrade vanadium carbides. The thought is that because the large AlOx particles in a coarse abrasive can't get between the carbides, they can't get at the softer steel matrix so they don't preferentially abrade the matrix. Presumably finer AlOx or SiC particles will be a able to get in between the carbides to abrade the steel matrix.

It's not entirely clear at what grit the transition to abrading the matrix takes place. I guess that it probably depends on the carbide size and carbide volume.

This theoretically shouldn't be a problem with fine diamond abrasives. However it should be noted that the Science of Sharp electron micrographs show that various grits of diamond plate produce very different scratch patterns to similar grits of traditional abrasives and (somewhat counter intuitively) sometimes finer plates produce deeper scratches.

 

[gc0220]

I guess carbide pull out is a potential issue if you can't get the knife very sharp despite thorough burr control and deburring. In this case, I'd try a less acute angle or a microbevel.

The guy over at Science Of Sharp showed that coarse AlOx will abrade vanadium carbides. The thought is that because the large AlOx particles in a coarse abrasive can't get between the carbides, they can't get at the softer steel matrix so they don't preferentially abrade the matrix. Presumably finer AlOx or SiC particles will be a able to get in between the carbides to abrade the steel matrix.

It's not entirely clear at what grit the transition to abrading the matrix takes place. I guess that it probably depends on the carbide size and carbide volume.

This theoretically shouldn't be a problem with fine diamond abrasives. However it should be noted that the Science of Sharp electron micrographs show that various grits of diamond plate produce very different scratch patterns to similar grits of traditional abrasives and (somewhat counter intuitively) sometimes finer plates produce deeper scratches.

Right, but he was testing diamond plates. DMT diamond plates if I recall correctly, which are quite unique and perhaps not well understood. Their grit ratings are really just relevant to the particle size, but because those particles are embedded in a metal substrate statically, the smaller particles are actually cutting the same depth. The end result is that is a scratch pattern that isn't like what you'd find on a whetstone at all, and seemingly counter-intuitively, at least until you understand what's happening, the higher grits seem to remove MORE stock. Which makes sense based on there being more surface area with more particles of a smaller size. I had noticed that particular peculiarity in my subjective testing of some of these products, but it was nice to see it validated. This is also the same reason for a long time diamond plates didn't come to market in grits above say "1200" grit. There's some tomfollery happening here.

As far as getting the thing sharp. I honestly believe most people just aren't very good at sharpening things, and especially when it comes to freehand sharpening on whetstones. Throw in other variables like steels that don't play nice, such as something like D2, and most people are just hopeless. When I was first learning any time I'd try to step up past the sharpening grits and onto a polishing/finishing stone, like say from the 2k shapton pro to the 5k shapton pro, the end result was a blade that was duller than what I got from the 2k. It didn't take long with actually trying to improve to fix that problem. Now I'm able to touch up R2 knives on the finest and hardest splash and go stones and end up with a result that's objectively extremely keen, as demonstrated by effortlessly slicing through hanging paper towels and also free hanging hairs.

I think this is why so many people rave about knives made from steels like super blue. It's very easy to get it sharp, and achieve a level which for most people they're helpless to attain on any kind of abrasion resistant steel. Even the cheapo stainless steels you find in budget mass market knives, even at much lower hardness, mid 50's is going to have more abrasion resistance and be much harder to sharpen than the best and hardest white steels.

As usual I probably forgot several things, but that's what I got for now.

Oh, as far as what grit is relevant. I only have personal experience and even then I don't find it relevant to the vast majority of steels commonly used in Japanese kitchen knives, even R2, but in the case of something like ZDP which is basically 1/3 carbide and hardly a steel at all, I find that that transition point happens around the 3k mark. 3k in JIS land, cuz let's be real I've seen American made stones claiming to be 10k that leave the same finish as a 3k chosera. I've seen cheap China made stones claiming to be 8k that are 800k at best. Anyway, if you have a bunch of say ZDP knives and like highly refined edges, that's when something those naniwa diamond stones, at 3k and above, are quite handy.

 

[miggus]

particularly with edge trailing methods, you're gonna get some burr action big time. I didn't even mention how to deal with that if it comes up.

That is true! But no problem, I got that a burr will form and needs to be removed. I assume this is a major part of the learning curve for me, because burrs are much less tenacious on the carbon knives I'm used to sharpen.

Another thing that slipped my mind was asking what sort of knife profile he was working with, as it would have been relevant to know and adjust the advice and whatnot.

Also no problem! I got a set while I was at it: 250 K-Tip, 165 Nakiri and 150 Petty.
For now, I'm starting with the shorter knives, since that will reduce complexity until I have adjusted my technique.

Even though the gentle, even curve the gyuto has shouldnt be too challenging either.