Asymmetry – The REAL DEAL

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Dave Martell

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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
 
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great post, Dave! it took me quite a bit of trial and error to figure this out, i wish i had had this post a few years ago!
 
I would have to add that you can, technically speaking, have an asymmetric edge without changing angles--all you have to do is remove more metal from one side than the other. Then the cutting edge is no longer in the middle, and, by definition, the edge is asymmetrically ground. The problem with that(other than trouble wearing down the shoulder, having to grind off all of the maker's intended primary & secondary bevels, etc) is that it won't cut properly. This is the crux of all kitchen knife design--that understanding of the ENTIRE KNIFE is what creates a good cutting tool.

It won't cut properly because if the angles aren't set right to compliment the blade, and the angle is nice and low like we all like on hard Japanese knives(giving it a wide bevel), it will steer and cut funny. If you put an asymmetric edge on a 50/50 ground knife(that was never meant to have one) it will steer like CRAZY unless you adjust the angles. Some people get used to this by learning to cut at a slight angle, or griping the knife tighter on the blade face, but there is no need for this kind of exhausting and uncomfortable adjustment.

Japanese knives, and almost every good knife, is ground by someone's hands holding it to a belt or stone. It's not a mathematically driven process, and it's not that complicated--learn to know when you are hitting the edge and/or the shoulder(say, with the marker trick or whatever), and then do that.


Feel free to edify me if you disagree, Dave.
 
Great post! Just a little provocative: how do you explain European knives to come with asymmetric (left convex, right almost flat) blades and symmetric edges?
 
So if you sharpen the knife incorrectly as outlined in the posts above, why does that lead to problems with cutting?

And let's say the maker's bevels are hard to figure out or you have messed up bevels. How do you decide what the appropriate sharpening angle is for each side of the knife? Also, do you still grind less on the backside in addition to adjusting the angle, or do you adjust the angle and grind the same amount.
 
So if you sharpen the knife incorrectly as outlined in the posts above, why does that lead to problems with cutting?

That's what I was hoping to clarify, because it is the sticking point for me. Sorry if I wasn't clear. It leads to steering--the knife pulls one way or the other, and will either slide out of the food(especially if it's hard like a carrot or potato), or it will slide into the food and just cut really crappy because of the resistance.

Think of it like trying to balance a board on it's edge on the front of a boat(clearly impossible, but it's just an illustration--I'm not Jesus here). If the boat is symmetrical, and the board is centered, it will stand on it's edge, the water would simply push it up against the boat hull. If you turn it the slightest bit, it will fly right off, because the boat is pushing where it is going no matter what that board is doing. If the board is part of the boat, it will make the boat turn. This is how a rudder works, and it's also how your edge interacts with your knife.

If you had a boat designed to be differently shaped and larger and heavier on one side than the other(terrible idea for a boat), you would have to move the rudder to the center of mass, not the geometric center, but even then, the boat will be trying to turn all the time, because the boat is being pushed evenly by the sail/props/whatever. So it has to be pointed at an angle, like driving a car with misaligned wheels, in order to go straight. Or you can move the props so that it is being pushed unevenly and it will compensate.

In this case, the rudder is the edge, the boat is the knife, and the sails/props is your hand applying force. Either you adjust the way you apply force on the knife(by holding or using it differently to compensate for it's tendency to steer), or you change the angle of attack and it will do the work for you.


If the knife is being pushed through food, it is meant to be guided as a whole object--not just an edge. So the edge has to be pointing where the blade is wanting to go, or else it will be cutting in a different direction than the knife is wanting to go.
 
...... how do you explain European knives to come with asymmetric (left convex, right almost flat) blades and symmetric edges?


If the knife came from a factory then I'm guessing it's poor workmanship, if it came from an individual maker then it's someone being cheeky.
 
I would have to add that you can, technically speaking, have an asymmetric edge without changing angles--all you have to do is remove more metal from one side than the other. Then the cutting edge is no longer in the middle, and, by definition, the edge is asymmetrically ground. The problem with that(other than trouble wearing down the shoulder, having to grind off all of the maker's intended primary & secondary bevels, etc) is that it won't cut properly. This is the crux of all kitchen knife design--that understanding of the ENTIRE KNIFE is what creates a good cutting tool.

It won't cut properly because if the angles aren't set right to compliment the blade, and the angle is nice and low like we all like on hard Japanese knives(giving it a wide bevel), it will steer and cut funny. If you put an asymmetric edge on a 50/50 ground knife(that was never meant to have one) it will steer like CRAZY unless you adjust the angles. Some people get used to this by learning to cut at a slight angle, or griping the knife tighter on the blade face, but there is no need for this kind of exhausting and uncomfortable adjustment.

Japanese knives, and almost every good knife, is ground by someone's hands holding it to a belt or stone. It's not a mathematically driven process, and it's not that complicated--learn to know when you are hitting the edge and/or the shoulder(say, with the marker trick or whatever), and then do that.


Feel free to edify me if you disagree, Dave.


Nothing for me to disagree with here.
 
Thanks Dave-U da Man. I need to print this up on a card so I can explain it better to all the people that think I'm nuts. I always draw a blank when I try to put it into words. You forgot to put an MMMkay in it though.
 
And let's say the maker's bevels are hard to figure out or you have messed up bevels. How do you decide what the appropriate sharpening angle is for each side of the knife? Also, do you still grind less on the backside in addition to adjusting the angle, or do you adjust the angle and grind the same amount.


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.
 
I agree with the intent of the post. That is, that grinding asymmetry into your edges isn't as simple as it might seem but as far as how much wiggle room you actually have to work with, I'd say you have a lot more than this thread makes it seem. Whatever is done to one side if the bevel just has to be balanced in one way or another on the other side to avoid steering. I see steering as more of a trade-off than something to be avoided at all costs. It just depends on the knife, the material being cut and the user. There's a lot of room for wiggle and don't tell me the fool that sharpened my A-type had any sort of geometry in mind when he ground that haphazard POS bevel. :)
 
I agree with the intent of the post. That is, that grinding asymmetry into your edges isn't as simple as it might seem but as far as how much wiggle room you actually have to work with, I'd say you have a lot more than this thread makes it seem. Whatever is done to one side if the bevel just has to be balanced in one way or another on the other side to avoid steering. I see steering as more of a trade-off than something to be avoided at all costs. It just depends on the knife, the material being cut and the user. There's a lot of room for wiggle and don't tell me the fool that sharpened my A-type had any sort of geometry in mind when he ground that haphazard POS bevel. :)


I completely agree with you on all points.


Just to explain a bit more though, 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.
 
Thank you Dave .
Great post

and yet this forum is still thriving .
 
Interesting post. I do not know if this Q belongs in this thread or not, so if not, mods, please separate!
I am a lefty (I know challenged...)
How do i best approach this assymetry that comes from the original blade grind?
How do you other leftys do?

Thanks
 
Interesting post. I do not know if this Q belongs in this thread or not, so if not, mods, please separate!
I am a lefty (I know challenged...)
How do i best approach this assymetry that comes from the original blade grind?
How do you other leftys do?

Thanks


It's been my experience (with double beveled knives like gyutos) that most lefties buy righty knives and find grinding more on the left side than the right helps make the knife feel better to them. I think a good place to go for lefties is to get a thinner 60/40 gyuto as a starting point since this is much less likely to cause problems.

Now when you're talking about double beveled knives such as the honesuki & garasuki that are 90/10 ground as well as single beveled knives you'll either have to learn to use the right handed versions or pay the premium for the lefty versions, no way around this.
 
Assuming the following assumptions are true (gathered from this thread, but may have wrongly interpreted)

1. Sharpening the edge on both sides at the same angle can create asymmetry and put the edge where you want it to be relative to the spine
2. Sharpening the edge on both sides with a different angle on each side can create asymmetry and put the edge where you want it relative to the spine
3. Both methods can put the edge in the same spot
4. The key difference between the two is ONE angle (left or right side depending on what he blade wants)
5. This angle will either either widen (steeper angle) or narrow (shallower angle) the bevel.

Example: I sharpen one side at 15*, the bevel may end up being 0.3mm wide. I now sharpen this to be 7.5* instead and end up with a bevel 0.6mm wide.

Again using either method (same angles vs. different angles) will put the edge in the same spot relative to spine. One method achieves this by grinding more vs. less. The other method uses different angles.

Assuming the above is true the only difference in the end result is the width of the bevel on one side. Using 15* vs. 7.5* this difference may be 0.3 per above example.

Question (finally): Does this 0.3mm difference in bevel width really make all the difference in whether a knife steers or not (or at least less)?

Based on the posts here the answer should be yes. Personally I can see this being the case with very thick blades (that should maybe be thinned) or single bevel knives, but with lasers that have a barely perceptible edge I see this not so much. If someone could elaborate on this more that would be great. Still wrapping my head around all this.
 
Assuming the following assumptions are true (gathered from this thread, but may have wrongly interpreted)

1. Sharpening the edge on both sides at the same angle can create asymmetry and put the edge where you want it to be relative to the spine
2. Sharpening the edge on both sides with a different angle on each side can create asymmetry and put the edge where you want it relative to the spine
3. Both methods can put the edge in the same spot
4. The key difference between the two is ONE angle (left or right side depending on what he blade wants)
5. This angle will either either widen (steeper angle) or narrow (shallower angle) the bevel.

Example: I sharpen one side at 15*, the bevel may end up being 0.3mm wide. I now sharpen this to be 7.5* instead and end up with a bevel 0.6mm wide.

Again using either method (same angles vs. different angles) will put the edge in the same spot relative to spine. One method achieves this by grinding more vs. less. The other method uses different angles.

Assuming the above is true the only difference in the end result is the width of the bevel on one side. Using 15* vs. 7.5* this difference may be 0.3 per above example.

Question (finally): Does this 0.3mm difference in bevel width really make all the difference in whether a knife steers or not (or at least less)?

Based on the posts here the answer should be yes. Personally I can see this being the case with very thick blades (that should maybe be thinned) or single bevel knives, but with lasers that have a barely perceptible edge I see this not so much. If someone could elaborate on this more that would be great. Still wrapping my head around all this.



Hi Clayton, I'm not sure that I can agree with all your extrapolations but assuming that your math is correct I'll answer about the issue of whether or not such a small amount (you mentioned 0.3mm) difference between the angles on the right and left side being a factor in a thin laser knife steering or not - I say probably not. It's unlikely that mistakes made on a really thin 60/40 ground knife will make that much of a difference but it is likely that some effect will occur over time. The thicker knives will be less forgiving earlier on.
 
Thanks Dave. When you say "but it is likely that some effect will occur over time" - Do you assume that the user is not thinning the blade?

Assuming they are thinning the blade over time, would the impact or "non-impact" of same angle vs. different angle not remain steady?
 
Sorry, may have been clumsily phrased. Let me try again:

When you say "but it is likely that some effect will occur over time". Is that a function of the "shoulders" growing further appart (i.e.: blade becoming thicker behind the edge) over time due to sharpening without thinning? If not, how does the effect occur over time?
 
Well based on the maths of it, any error that's introduced due to the incorrect positioning of the edge and angles to said edge can only get more pronounced as the blade gets thicker. (i.e. it's also the reason that if you're 1* off when you're shooting a bb gun at a board 30' away you'll probably still hit (1* over 30' = 6" off target), but the same 1* difference over 100' means that you'll miss (1' 9" off target))
 
Sorry, may have been clumsily phrased. Let me try again:

When you say "but it is likely that some effect will occur over time". Is that a function of the "shoulders" growing further appart (i.e.: blade becoming thicker behind the edge) over time due to sharpening without thinning? If not, how does the effect occur over time?


I was referring to taking the edge away from matching the blade's asymmetry.
 
I was referring to taking the edge away from matching the blade's asymmetry.

Which will get worse over time because the shoulders grow further appart?

Would the edge not also move away over time from matching the blade's asymmetry if we use different angles?

Seems like appropriate thinning should solve the issue with both methods, no?

Dave, please let me know if I am out of line with my questions. I would completely understand if concrete answers fall into the "trade secret" category.
 
great post Dave :doublethumbsup:

LOTS! of misinformation around the interwebs.
 
I was referring to taking the edge away from matching the blade's asymmetry.

Which will get worse over time because the shoulders grow further appart?

Would the edge not also move away over time from matching the blade's asymmetry if we use different angles?

Seems like appropriate thinning should solve the issue with both methods, no?

Dave, please let me know if I am out of line with my questions. I would completely understand if concrete answers fall into the "trade secret" category.


All questions are welcome but I'm having trouble understanding what you're asking, sorry.
 
Here is drawing illustrating the difference (from what I gather) between using "same angle less abrasions" vs. "different angles". I understand this is just one possible scenario, but key difference would only occur on one side of the blade and would manifest itself in the highlighted yellow portion of the drawing.

6997752179_561bf87c1d_c.jpg




All in all the two methods do actually appear to create two different edge profiles, at least they do on my drawing. Question is does it matter or is one "better" than the other.
So far, I don't know. but could see this mattering much more on thicker knives. Meaning thickness plays a role which is also why it gets worse over time IF you don't thin the blade.
 
Clayton, I would think that these two scenarios do offer different results. I'd like to point out that my opinion of doing either (as an absolute) isn't the best way to go about it though, so if you're looking for one way to be better than the other so that you can follow that you'll be headed down the wrong path.

The correct way is to not use any formula or mathematical equation, work the bevels as they need to be worked. If it takes 10 min of grinding on one side and 2 min on the other or of you have to slightly tweak the angle for one side vs the other then do what you must to keep the asymmetry of the knife in tact which will in turn keep your knife cutting straight.
 
Thanks Dave!

Completely understand about not doing either as an absolute. I was really just trying to get to the bottom of the "vary sharpening angle vs. not vary sharpening angle from one side to the other" thing.

Looks like varying the angle can have some merits and might be possibly worth the "pain".
 
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