Sunday, March 18, 2012

Asymmetry – The REAL DEAL

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) and 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

      1 comment:

      Dave @ said...

      *Note - The reason why I mention steering as an unwanted by-product of improper asymmetrical sharpening is because of how many knives (literally hundreds upon hundreds) I've had to fix for people who caused themselves problems through either trying to do something special that read about on the internet (experimenting), simple lopsided sharpening over time, or from sharpening services that offer single sided sharpening only. The results are all the same regardless of what caused the condition, the knife owner wants to turn back the clock and fix the knife to steer straight again, sometimes this is simple (as is often the case fortunately) and sometimes not so simple. So while I agree that steering is a trade off of sorts (and maybe something even desirable to some) it's something best avoided by most. My post is meant to help the majority of people avoid the pitfalls of misinformed advice found across the interwebs.