Citation :
When we venture into using Japanese kitchen knives we often find that we’re interested in sharpening our own knives and begin searching for information on this subject. This leads us to research waterstones, sharpening techniques, and the subject of blade asymmetry inevitably comes up. Since this discussion is regarding asymmetry I’ll leave waterstones & techniques for another time.
What is asymmetry? For our discussion purposes (here within this community) we’re referring to how the knife’s blade is forged/ground in uneven amounts from side to side. While it’s the norm to have a blade be perfectly symmetrical in the western world it is uncommon in Japan to find examples of this. In my experience with working with thousands upon thousands of Japanese knives I can confidently state that 99% are asymmetric with the majority being ground favorably for a right handed user.
Common terminology:
100/0 (single bevel) – yanagiba, usuba, etc
90/10 (double bevel) – honesuki, garasuki, etc
80/20 , 70/30, 60/40 (double bevel) – gyuto, nakiri, sujihiki, etc
50/50 (symmetric) – non Japanese knife
Now I won’t go into why these knives are made this way as I’d only be speculating with regards to some of this. I have my theories and I’ve heard a lot of other’s views on this yet none completely convince me to be the true cause so I’ll leave this part of this subject alone. I will tell you very simply how you can deal with asymmetry and how to sharpen an asymmetric knife though.
To that end I first have to point out that you’re sure to stumble upon some information (I call them myths), while doing your research, that somewhat contradicts what I’ll be talking about here, stating that Japanese knives are ground or can be sharpened symmetrically (50/50) - I call BS on this. Also, you will see it stated that it is not required to change the angle of the sharpening stone arm when using guided (assisted) sharpening devices (like the EdgePro) when you switch from side to side - again I call BS on this.
I suggest that you consider the sources that you discover this information coming from as when I’ve done so I’ve discovered that in 99% of these cases I find that it is a Japanese knife retailer or a distributor of guided sharpening devices (and proprietary accessories like stones, etc) that make these claims. I believe that the reason for this is simple – they do not want you to know the REAL DEAL with asymmetry because if you were to know about it you would be questioning them on the proper ways to sharpen these knives (which is not an easy question to answer) and in the case of the guided devices you would come to the realization that they are more complicated to use on asymmetric knives – blades that they were never meant to originally deal with.
Here’s the REAL DEAL and what you really need to know – stripped of all BS and put in plain simple terms….
If you want your double beveled Japanese knife (which has a blade that has been either forged or ground asymmetrically) to cut straight and wedge less you will sharpen the edge bevels as close to matching the asymmetry of the blade itself. That’s it in a nutshell!
How can you do this? Simple…you look at the blade and mimic it’s asymmetric grind when working it’s edge bevel. I used to use a straight edge laid on the side of the knife to compare side to side and then follow by rough estimating this form while sharpening the edge bevel. Luckily most of you will have a new knife that you’re starting out on and you’ll likely find that this ratio has already been worked into the bevels and all you have to do is follow along.
Now let’s talk more specifically of how to sharpen asymmetric knives….
I always suggest sharpening any knife starting at the top of the current edge bevel (this is what’s referred to as the shoulder of the edge bevel – it’s the transition between edge bevel and blade face) and working your way down (by grinding/polishing/etc) to the cutting edge. Doing this will ensure that you don’t repeat the same angle (since repeatability is bad in sharpening) so that you always thin the edge bevel as it moves upward into the ever increasing thickness of the blade’s cross section.
When sharpening you should be stopping and checking your progress often so as to ensure that you’re on (or hitting) the correct location on the edge bevel. You should never aimlessly grind away steel without stopping and checking as doing so will ensure that you stay on the correct path through making incremental adjustments. If you see that you’re hitting the edge bevel too close to the cutting edge then lower the spine (which adjusts your angle of attack) to correct and if you’re hitting the edge bevel too high (above the shoulder of the bevel) then raise the spine (by adjusting the angle of attack) to correct.
Notice That I didn’t say that you had to use the same angle on each side of the knife nor did I say that you needed to change the angle for each side of the knife or to make each side different angled than one another?
So let’s take a fairly asymmetric gyuto as an example to work with here, I’ll use the Hiromoto AS series as this is easily a typical asymmetric 70/30 ground blade.
In this first case I will be freehanding (that’s using no sharpening guide or aid) on a waterstone. If I were to select one specific angle (let’s say 15deg - or as close to that as I can guess and hold steady) and just go at it I’ll see a couple of things happen. The first is that I’m not hitting the edge bevel where I want to, and I now regret not stopping to check what I was doing, and that the right side’s (if it’s a right handed knife) edge bevel is much taller than the left side is. So I used the same angle yet the right side’s bevel is taller than the left side’s bevel. Why? Because the blade is ground asymmetrically!
Now I take another untouched Hiromoto AS gyuto out of the box and lay it down on the table of an EdgePro, select an angle (let’s again pick 15deg - or as close to that as this device allows for) and then go at it again. What do we now see? Well we’ll likely have that same feeling that we had when freehanding, about wishing that we had stopped and looked before carrying on, but we also see that the stone hasn’t at all hit the bevel on one side of the knife like it did when free handing. Why is this? Because the blade is ground asymmetrically!
Unlike freehanding, where we adjust the distance between the spine of the knife and the stone’s face for angle approach, we instead (on the EdgePro) laid the knife down on a fixed position table and then swung the stone over the opposite side’s edge bevel. Why does this matter? Because the blade is ground asymmetrically – it’s not the same on both sides!
To revisit the issue of myths, many EdgePro type device retailers will tell you to just pick an angle and grind more from one side than the other or maybe to count strokes (like 7 strokes on this side and 3 on another for 70/30 grinds)…..they state that this will allow for correct asymmetrical ground edges. I respond to this by stating that this is an irresponsible solution to tell people to sharpen their knives this way as I know from my years of experience that this will only lead to an unevenly sharpened knife that steers and wedges while cutting.
So if you’re using an EdgePro type device and you have to adjust the stone arm’s angle for each side of the knife to properly hit the edge bevel in the correct position then do so. Yes this sucks but this is what you’ve decided to use to sharpen your asymmetric Japanese knives with. If you’re upset with having to do this then tell this to the people who sold you the myth, but sharpen your knives correctly.
Again people, these retailers don’t care if you get it right or not – they care about selling knives and sharpening systems (with those proprietary stones) so if you screw up it doesn’t matter one bit to them.
So let’s summarize….
1. All Japanese knives are asymmetric – the entire blade is asymmetric – not just the edge.
2. Use your mind and your hands to find the ratio of the blade and then mimic this within the sharpening of the cutting edge bevel.
3. Adjust your angle of approach as need be - yes even if using a sharpening aid/device.
That’s it folks – you now know the REAL DEAL
Happy sharpening!
Dave Martell
Suite (toujours Dave Martell)
Some maker's bevels are hard to figure out so this can be a problem - no doubt about it. You need to evaluate the blade's asymmetry and then replicate it as best as you can when working the edge and it's key to use some common sense here but ultimately there's no substitute for experience and this is only gained by trying.
If you want to play it safe (while freehanding) a new knife with less than clear factory bevels then I'd suggest starting on the right side (if it's a righty knife) and once I've figured out the appropriate angle for this side I'd flip the knife over to the left side and sharpen at the same angle. If you've done things correctly then these edge bevels should match up to the blade asymmetry pretty closely. If you've got it wrong you might not notice straight away, it might take a few more sharpening sessions for the blade to start twisting while cutting and if that happens you then adjust by grinding more on one side or the other.
*Note - EdgePro users grinding more to one side than the other or counting strokes (vs changing angles on each side as needed) as well as people freehanding on the easy side of the knife only (that's sharpening on the right side and deburring on the left) may fall victim to "it seems fine" syndrome. It may seem fine now but like I said above it might not seem fine forever.
Single Bevel Sharpening
There's no right or wrong answer to how you want to go about the initial sharpening and bevel shaping and subsequent edge maintenance to your knife, I will discuss here what I do....
My way on the initial sharpening is to first make sure the back side is good to go by flattening it using a 1k(ish) stone. I'm using very light pressure to make sure that this zero degree bevel extends to the cutting edge and nothing more. I do this because almost every new knife will come with a buffed bevel cut at a higher degree than zero - we must erase this and create the flat zero degree bevel or else your polishing stones will never touch the cutting edge. I'll then follow this 1k stone to polish when I do the front side later on.
Now I flip the knife over and cut my edge in using the same 1k stone. I cut this bevel at 1-2 degrees more obtuse than the blade road is ground. This means I lay the knife down flat on the blade road and then ever so slightly lift the spine to raise the knife off of the blade road and then sharpen the edge. This does two things, first it ensures that I've created a burr (in other words - an edge) and second it removes the often found obtuse factory edge. All I need to do is to grind a few millimeters in height at this angle and I'm good.
Next I flatten the blade road using a stone normally between 120x -500x. I start with the blade road sitting flat on the stone and if everything goes correctly I'm grinding up to the shinogi line at the same time I'm headed down to the edge. Most often I hit the shinogi line just as I'm hitting the top of the edge bevel that I cut in using the 1k stone in the previous step. Once I've made the blade road even so that along it's length it is one even grit pattern from heal to tip and shinogi line to my 1k edge I stop. I will do a bit more to get the blade road to extend down (just) into the 1k edge because this is important to what I do later.
Then I move onto a finer stone (like the King 800x). I use this for just a minute to even out the appearance of the two bevels to make them look the same grit level. I work the blade road first and then, while still moving, I raise the spine to remove the blade road from the stone to hit the cutting edge bevel (previously cut with a 1k edge). Once it all looks even as one large bevel I'm finsihed with this stone.
I follow with a finer stone (like an aoto), first honing the flat zero degree bevel on the back side and then working the blade road and edge bevel exactly as I did with the 800x stone, again stopping when it appears as if they're one smooth bevel. The point in working both the 800x and aoto in this manner is to blend the two bevels together. In working them the way that I do I create a hamaguriba (clamshell/convex) shape at their union.
Now it's time to polish...
First up is to work the back side zero degree bevel using a polishing stone 6k-10k. I'm looking to put the keenest slicing edge that I can on a yanigba where all other single bevels benefit more from a slightly toothier edge. Choose your finishing stone based on your application/needs.
Then using the same stone it's onto the front side, to the cutting edge.
Most often I isolate the cutting edge again at this point (just like I did at the beginning with the 1k) and hit just this bevel - seperate from the blade road bevel. If you just hit the edge bevel you're done, if you hit the entire blade road you need to then go back over the blade (ONLY) with the aoto again to make it look pretty. This extra work does look sweet when done correctly but it's just for looks really, not much other benefit...although on some cladding it can add a level of slipperyness to the surface texture, much like what can be achieved through the use of natural stones. It makes for a shiny matte finish - make sense?
Next up is stropping...
For most all single bevel knives I'm using felt and diamond spray today. I like what this adds to the edge but for a knife like a yanagi I'm looking (again) for a smooth slicer so I'll use the felt/diamond but I follow it with felt loaded with 0.3 micron chromium oxide. The edge becomes "softer" because of the effects yielded by round particles of the chromium (versus the blocky coarser structure of the diamond particles).
If everything has been done right to this point I've now got a 98-99% flat blade road with a hamaguriba shaped edge. I've added edge strength by increasing the blade road angle and at the same time I've reduced the amount of friction by rounding the transition between blade road and edge bevel and I've also increased the edge strength by using a convex grind. The texture should be somewhat slippery when wet to aid in non-sticking and food release.
For future touch ups it would be recommended to use felt/diamond and felt/chromium oxide and when that doesn't work it's back to the polishing stone, both front and back, (but only) hitting the front side edge bevel - not the whole blade road. Then back to the strops.
Eventually this won't work that great and then it'd be advised to go back to the aoto where you work both sides again and then back up through the polishing stones and strops. Of course after that it's time to start all over again with the 1k although it's important to note that if at all possible all back side zero degree work should be (after initial sharpening) preformed with polishing stones only. Keeping the wear to a minimum to the backside (ura) is critical to the lifespan of these knives.
I believe my way of doing this offers a good way to get max performance, ease of sharpening, and good bevel/shinogi correction over time.
Hope this helps...
Dave
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![[:da_s_monk]](https://forum-images.hardware.fr/images/perso/da_s_monk.gif "[:da_s_monk]")
Plus kitch que ça, tu meurs... une telle débauche de technologie pour la face cachée (alu usiné CNC dans la masse, aimants samarium cobalt...) et une face visible aussi triviale (pas 2 bouchons alignés), ça me laisse sans voix (heureusement j'ai encore mes doigts pour écrire!)![[:moonzoid:2]](https://forum-images.hardware.fr/images/perso/2/moonzoid.gif "[:moonzoid:2]")
<Mode chauvin OFF> 
) fait pour, avec la fente qui va bien (tiens !! cela me rappel une poésie 
"Ô merveillette fente ....." )![[:tinostar]](https://forum-images.hardware.fr/images/perso/tinostar.gif "[:tinostar]")
![[:tomatookc]](https://forum-images.hardware.fr/images/perso/tomatookc.gif "[:tomatookc]")
