Asymmetry – The REAL DEAL

[Dave Martell]

:thumbsup:

 

[zitangy]

Wait, I have a 2 questions that I don't think has been addressed regarding kens demo. 1) why the hell would you have to set the platen to any degree of a angle? I mean at any degree is it not still the flat platen and edge angle going to be the same?

Assuming that I am on the mark.....
For sharpening, My Belt grinder's platten is set at angle ( Platten is not parallel to the belt) so that one end is almost in contact adn the other end further away form the belt. The greater the slack, the greater the convexity and also the secondary edge . The closer the platten is to the belt less slack and less convexity with smaller secondary edge.

I also put the vertical grinder at 10 degrees so that when when I run the blade at 0 degrees ( knife upright with edge facing down) I have 10 degrees and with it tilted slightly towards me.. it wld be greater than 10 degrees.

Hope that this answers your question.

Rgds
D

 

[Mancinism]

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

Thanks for you precious experience and advices! really good information to know!

 

[daddy yo yo]

regarding steering:
1) what direction would a right-handed knife with 70(r)/30(l) sharpening steer assuming it was originally a 50/50 grind?
2) would an asymmetric bevelled knife such as hiromoto AS (60/40) or misono sweden steel (70/30) steer to one direction? i guess not because they are ground asymmetric?!

 

[Benuser]

Very hard to speak about it in general terms, as always, it depends...
Just to give some directions to your thoughts:
Have a look at the friction the very edge and the area immediately behind it encounters.
I had a very asymmetric blade, with both sides sharpened at the same angle, but strongly off-centered. It steered clockwise. By convexing the right side, and increasing the left angle without any convexing I could reduce the friction at right, and enhance the friction at the left side.
Another factor is the user's wrist position, and his grip.
Don't believe people who tell you the Misono is ground 70/30, and the Hiromoto 60/40. All you may say is they are asymmetric. About the Europeans: they are just as asymmetric, just the edge is well-centered to meet left-handed.

 

[Benuser]

Just to add: in my experience most Europeans -- supposedly symmetric -- blades benefit highly by some asymmetry when sharpening. If you want numbers, let's say: 60/40, 12/15 or so.
But these numbers aren't that relevant if you're sharpening an existing knife. If you're happy with its performance you'll stick with the existing geometry. If you have any issue with it you will change it accordingly. Without a pressing need you won't even consider to move the very edge from its place I hope.

 

[Dave Martell]

Again people, these retailers don’t care if you get it right or not – they care about selling knives and sharpening systems............so if you screw up it doesn't matter one bit to them.

The following is taken from another forum where a retailer is giving poor (well - false) information to a potential customer. (The names & links have been removed) This is a great example of what I hear about all of the time, what I was referencing in my quote above.


From the customer...

Hiromoto 60/40 does it matter?

Hi ****,

I have a question about the Hiromoto knives you offer. I was considering the 210 gyuto and a paring knife, but I read on another site that Hiromoto knives have a 60/40 bevel? Is this the case? I'm a lefty so it does make a difference. If they only come with a 60/40 bevel, are left handed versions available?

Thanks!
*****

From the retailer...

Hi *****,

It makes no discernible difference when you use the knife and once you sharpen it you can easily sharpen it evenly if you like. If you are really hung up on the tiny asymmetry you can choose the finish sharpening service and we will sharpen it evenly before we send it out.

Hiromotos are more like 70/30 than 60/40, very asymmetrical. "Finish sharpening" evenly (once) will do squat (well besides taking your money) but if done a couple more times you'll be sporting a steering wedge monster.

He never addresses the customers need for a left handed knife.





From another member who's trying to help....

Given that it looks like the blade itself is symmetrical, a 60/40 edge bevel should not cause any issues. Chances are that unless you work to keep the bevel you'll get it to a 50/50 bevel through sharpening anyway. Shouldn't be a big deal at all.

Now if the blade itself was ground for a righty, then you might have some issues.

Hiromotos (like all Japanese knives) DO NOT have symmetrical blades. Again, Hiromotos are 70/30 (very asymmetrical). No you won't get a 50/50 bevel through sharpening, you will get what you apply to the knife.

The blade IS ground for right handed users.

This all goes uncorrected by the retailer.




Ignorance, stupidity, arrogance, or deceit.....I don't care....it's wrong info either way. :bashhead:

 

[Geo87]

Ignorance, stupidity, arrogance, or deceit.....I don't care....it's wrong info either way. :bashhead:

Or all of the above

 

[Benuser]

That's funny. I found recently a salesman -- probably another --praising a Misono's symmetry...

http://www.chefknivestogoforum.com/viewtopic.php?f=4&t=4245&hilit= Misono

 

[Dave Martell]

That's funny. I found recently a salesman -- probably another --praising a Misono's symmetry...

http://www.This Site Not Allowed Here.comforum.com/viewtopic.php?f=4&t=4245&hilit= Misono

That's another one, blatant BS for anyone who knows these knives.

 

[rogue108]

What do lefty's do who want a Hiromoto ?

 

[Dave Martell]

What do lefty's do who want a Hiromoto ?

Besides ordering a left handed knife? Well that is if one is available and if they don't mind paying the 30% upcharge. No wonder this doesn't get brought up by the retailer, too easy to lose a sale.

I suppose most will live with the right handed asymmetry. Some will grind more on the left (when sharpening) then on the right. Not many options here.

 

[Benuser]

Masahiro offers standard carbon blades, with the entire geometry adapted for left-handed. Right side flat, left side convexed. Some 25% more than the common right-handed ones.

 

[JBroida]

some knives can be adjusted at the edge while others need to be reground through a process somewhat similar to thinning, but geared towards changing the blade geometry with regard to asymmetry

 

[Robert]

I'm still confused ;I have checked some knives with a protractor,I laid the knife with the flat side on the table (if they have one)and measured the angle between the flat side and the edge.If I understand correctly there must be some difference in angles.
Arcos chef knife 21cm(spain) left; 3 degr and right 3 degr no flat side.
Tojiro dp gyuto 24cm 3 2 flat side
Watanabe sanuko 17cm 3,8 3,8
watanbe nakiri 16 cm 3,3 3,2
watanabe petty 12 cm 4 4,6

I not see asymmetrical sides or maybe I do something wrong?

 

[WarrenB]

Ok from what I have gathered on double bevel knives the cutting edge of the blade will remain in line with the spine regardless off the 70/30 60/40 etc split, so when you lay the blade flat you are measuring the angle from cutting edge to side of the blade so it will always be the same, if you measure the angle from the cutting edge to secondary bevel you will get the 60/40 etc angle. The grind on one side will be higher up the blade creating the asymmetry. Someone please correct me if I am wrong:dontknow:

 

[Geo87]

I believe you are on the wrong track there warren. The edge is not centred under the spine. It's more offset to one side due to the asymmetrical edge grinds: grinding more from one side moves the very edge around. Also it's not just at the edge level but the blade face is also ground asymmetrically. You can really see it if you closely examine the choil. ( someone correct me if that's wrong )

 

[WarrenB]

I believe you are on the wrong track there warren. The edge is not centred under the spine. It's more offset to one side due to the asymmetrical edge grinds: grinding more from one side moves the very edge around. Also it's not just at the edge level but the blade face is also ground asymmetrically. You can really see it if you closely examine the choil. ( someone correct me if that's wrong )

Back to the sharpening dvd then:lol2:

 

[Geo87]

Back to the sharpening dvd then:lol2:

To be honest, Asymmetry can be a confusing subject. It was, and still is for me and I'm sure a lot of people would agree. I spent far too long researching the subject I must admit and it drove me crazy! But I've learnt enough to get knives to cut straight and wedge less and that enough for me!

I've found if you first test the knife by cutting a dense item. If it cuts straight and doesn't wedge much then follow along with the current bevels, proportions etc when sharpening

If it does not cut straight and or wedges then you may need to adjust the location of the edge and or thin behind the edge to fix the problems

For example : my 270 fkh gyuto (80/20) OOTB pulled majorly to the left.
At the advice of another member I slightly recentered the edge by creating a larger bevel on the LHS. The plan was to increase friction on the LHS and decrease it on the RHS.
Then the knife cut straight but wedged a little. I then thinned the knife equally behind the edge on both sides now it cuts beautifully.

I hope that helps a little... Try not to go insane figuring out the great mysteries and just focus on doing what you have to do to get your knife to perform right

 

[ThEoRy]

focus on doing what you have to do to get your knife to perform right

I make shiny things get cutty cutty. :knife:

 

[Benuser]

Glad to hear you've got good advice, Geo87. One point I would like to add: be sure to have a loose grip. In my country apprentices learn to have a "firm" grip with their Wüsthof, and if a knife behaves differently than they're used to, they tend to make that grip even firmer. Which leads to disasters with asymmetric blades that steer somewhat. But in general, balancing friction on both sides seems to work well, indeed.

 

[liren1]

I was mentioned earlier that some knives can be switched from right to left at the edge only.
I would assume that this is only possible for knives that are symmetrically ground, and only the edge is not symmetric. Is that a correct assumption ?

 

[Benuser]

See in this same thread post nr 102 and further. It might work to some extend with very thin blades.

 

[Sherski]

Could someone kindly have a look at my knife and help me out? I don't know if it is me or if this knife is left-hand biased in its assymetry. I'm a righty who bought this cheap buho funayuki as a light prep knife but one day at work I felt the blade 'side-tracking' to the right, like a dog that pulls on your leash but ever-so-slightly. This was when I was cutting red cabbage and was about 60-70mm off the board at its highest point where the cut commenced.

I know choil shots arent the most helpful when it comes to determining asymmetry or detecting irregularities in grinds but I figured it might be a place to start. Can someone share whether or not the grind is just another example of a lazy job and how i should go about treating it?

 

[schanop]

It does look like a left hand biased knife from choil shots. Raising bevel height on the left hand side might help.

 

[schanop]

Oops, I meant the other way around. Or explicitly convexing the right hand side, making it more like hamaguri/strong hamaguri edge.

 

[Marko Tsourkan]

It's hard to say for certain, but it looks to me that knife in the picture two posts above is symmetric.

I will try to explain asymmetry in a simple fashion. Visualize a line at the center of same thickness blank, say 3mm thick, so the line will be exactly at 1.5mm. You will get a symmetric knife if both sides are ground to that line. Now, move this line off center somewhat and grind to it. On one side you will have a larger convex radius than on the other (I assume that the knife is ground convex, not flat, though even flat grind will result in asymmetric grind). The larger convex side will be your cutting side.

That is how you get asymmetry. The 60-40, 70-30, 90-10 are not asymmetry, it's the bevels that are cut into the edge. Imagine that you grind a knife symmetrically to say .5mm thickness at the edge, then cut a wide bevel on the right side and debur on the left. You get 90-10, but the knife is still symmetric, as far as the grind is concerned. These bevels are typically done to make sharpening easier and to make do have some minor advantage in cut initiation.

Hope this helps.

Marko

 

[Geo87]

Great explanation marko.

Sherski: as far as my understanding goes... Your edge is like the rudder of a boat. It tells your knife where to go. If your knife pulls to one direction you need to adjust the location of the very edge. If it pulls right then cut a bigger bevel on the right. That will re centre your edge slightly and hopefully you'll be pointing strait. Keep making adjustments until your happy.

 

[erikz]

I'm not a pro or an expert at all Sherski, but this is how I would analyze the blade:

I would expect this knife to steer a bit as well...

 

[Mucho Bocho]

Thanks for the illustration Erik. Very helpful