Asymmetry – The REAL DEAL

[Dave Martell]

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….
All Japanese knives are asymmetric – the entire blade is asymmetric – not just the edge.
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.
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

[EdipisReks]

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!

[Eamon Burke]

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.

[Benuser]

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?

[heirkb]

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.

[Eamon Burke]

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.

[Dave Martell]

...... 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.

[Dave Martell]

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.

[knyfeknerd]

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.

[Dave Martell]

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.

[Dave Martell]

You forgot to put an MMMkay in it though.


Oh Snap! :D

[HHH Knives]

Fan-Damn-Tastic Dave!

Thank you for posting!!

[tk59]

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. :)

[Dave Martell]

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.

[steeley]

Thank you Dave .
Great post

and yet this forum is still thriving .

[RobinW]

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

[Dave Martell]

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.

[clayton]

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.

[Dave Martell]

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.

[clayton]

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?

[Dave Martell]

I couldn't say, anything could happen ....or not

[clayton]

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?

[dragonlord]

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))

[Dave Martell]

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.

[clayton]

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.

[memorael]

great post Dave :doublethumbsup:

LOTS! of misinformation around the interwebs.

[Dave Martell]

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.

[clayton]

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.

http://farm8.staticflickr.com/7239/6997752179_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.

[Dave Martell]

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.

[clayton]

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".

[Dave Martell]

I thought of another example that might help clear this matter up some.

Let's this time use a honesuki (a double beveled 90/10 ground knife) as our test mule. We'll use a right handed version here for our discussion.

So this is a knife that's a bit thicker than a gyuto is and much more asymmetrically ground.

Here's a picture of the right side of the knife....

http://www.watanabeblade.com/english/pro/honesukis1.jpg (http://www.watanabeblade.com/english/pro/honesuki1.jpg)


Here's a picture of the left side of the knife....

http://www.watanabeblade.com/english/pro/honesukis2.jpg (http://www.watanabeblade.com/english/pro/honesuki2.jpg)


You should note that the edge bevel on the right side of the knife is significantly taller in height than the bevel is on the left side, in fact the left side edge bevel is almost difficult to see at all.

This is a good example of how you can not use the same angle when sharpening both sides of the knife and that's true for both free handing and using a guided device.

If you're free handing the spine will have to be further away from the stone on the right side of the knife then when compared with the left side but only by a small amount. This is to adjust for the thicker blade.

If using a guided device (like the Edge Pro) it is easy to see (in use) how you must change the angle of the stone arm. What happens is say we choose the left side (the side with the very small bevel) to sharpen first. We lay the knife down onto the flat table and then adjust the stone arm to hit this edge bevel correctly, making about a 1-2mm bevel at the very cutting edge. When we flip the knife over to the right side (the side with the large bevel) we immediately see that the stone is hitting above the edge bevel on the right side. Why? Because the knife is nearly flat on one side and has a large wide bevel on the other side - it's asymmetrical.



Now let's take a single bevel (a 100/0 ground) knife like a yangiba and sharpen this both using freehand and a guided device and what do we have happen? We see the very same things as we do with the honesuki (90/10) knife except the issue of having to use different angles is even greater enhanced for us to note and have to deal with.

Is there anyone who thinks that you can use the same angle on an Edge Pro (or even freehanding) for both sides of a yanagiba (by using the grind more on one side than the other method or the counting strokes method) and have it come out OK? I seriously doubt that I'll find someone who can show me this to be the case. Why? Because I know that I have to sharpen at least a 15deg bevel angle on the right side and then switch to 0 deg the left side. Why? because the knife is asymmetrical - FACT!

The very same principle/practice is true for all Japanese knives because they are all asymmetric, the amount of change that we make (or not) is dependent mostly on the amount of asymmetry of a particular style of blade as well as the blade's thickness. We can, but should not, ignore these simple facts if we want to properly sharpen our Japanese knives.

[clayton]

Thank you! This example just helped my head a lot. Makes perfect sense that I would have to adjust the arm's angle on the Edge Pro every time I flip the blade to accommodate asymmetry. It is starting to really come together for me now.

[memorael]

I think the best way of explaining why some people don't like guided devices for sharpening around these forums is pretty simple. A guided device does nothing more other than provide a sharp edge. If you want your knife to cut great than you definitely need to free hand IMO. So if all you care about is slicing paper with no effort take a guided device, if you care about cutting all sorts off stuff with ease then go the hard way and learn how to free hand.

As Dave mentioned there are no absolutes in sharpening, always adjust and adapt to make a knife work for YOU.

[geezr]

Thanks for this thread Dave. May save some of us from going down an a path of
sharpening/cutting frustration :eek2:

[apicius9]

##{}{%, this is longer, better thought through and more complicated than most of final papers I am reading right now... And I really only want reasonably sharp knives. Makes me want to reconsider pull-through gizmos again... ;) I still don't see the appeal in sharpening, sometimes it seems way over my small brain's capacity...

Stefan

[MadMel]

Thanks for this thread Dave. May save some of us from going down an a path of
sharpening/cutting frustration :eek2:

or pull us back from the brink...

[adletson]

So am I correct in saying that when a knife is described as being "90/10 right hand ground" that it means that the cutting edge is 90% offset to the right side? Like if you had a number line (1-2-3-4-5-6-7-8-9-10) that represented the total width of the spine of the knife, the cutting edge is sitting on the 9th place holder?

[stereo.pete]

This might explain why my Fujiwara FKH Gyuto can shave armchair and glide through printer paper just fine, but wedges like it has superglue on the sides of it when I go to cut carrots/potatoes. Just when I thought I was getting the hang of sharpening, good old Dave brings be back to square 1.

[El Pescador]

So am I correct in saying that when a knife is described as being "90/10 right hand ground" that it means that the cutting edge is 90% offset to the right side? Like if you had a number line (1-2-3-4-5-6-7-8-9-10) that represented the total width of the spine of the knife, the cutting edge is sitting on the 9th place holder?
yup

[heirkb]

yup

Really? With the spine up, edge down, tip facing away from you, the bevel is farther on the right side than on the left side? This doesn't make sense to me considering that on a right-handed single beveled knife, the edge will be at 0.

[adletson]

Okay. So essentially when we sharpen a knife that is asymmetrical, we are replicating the edge that was ground into the knife by the maker of the knife? Clayton's illustration shows that an asymmetric grind can be produced by:
1. Grinding less on the "10 ground" side of the knife than on the "90 ground" side of the knife or
2. Sharpening at a more obtuse angel on the "90 ground" side and a more acute angle on the "10 ground" side.
So the maker can achieve the "90/10" edge (or the edge at the 9th place holder) by either method he prefers and it is our job to find which method is used and replicate. Am I right?

[Dave Martell]

Okay. So essentially when we sharpen a knife that is asymmetrical, we are replicating the edge that was ground into the knife by the maker of the knife?

Maybe. You can use the maker's edge bevel IF you believe that it replicates the asymmetry of the blade and then once you do this you find that the knife cuts straight. There is no rule to follow here.



Clayton's illustration shows that an asymmetric grind can be produced by:
1. Grinding less on the "10 ground" side of the knife than on the "90 ground" side of the knife or
2. Sharpening at a more obtuse angel on the "90 ground" side and a more acute angle on the "10 ground" side.
So the maker can achieve the "90/10" edge (or the edge at the 9th place holder) by either method he prefers and it is our job to find which method is used and replicate. Am I right?


Wrong. I see gaps in both directions that if followed will lead you down the wrong path. You need to evaluate each and every knife and each and every edge bevel and adjust as necessary - this is the only correct answer.

[dragonlord]

So long story short, practice, practice, practice?

[bieniek]

I acutally have a Hiromoto AS and I thinned it down a little, the sides are still assymetric, less than in new knife though.

I sharpen edge 50/50, and do little convexing - maybe 4 or 5 angles togehter.

I can promise this knife cuts twice as good now as when it was new.

I sharpen left side of knife with left hand, its possible that my angle is different, but I think they are both pretty similar.
I read once on JCK that Hiromoto has two altering angles and the difference was 3 degrees between sides!! Good joke
I will never get to that kind of skill ever. No point trying.

[El Pescador]

Really? With the spine up, edge down, tip facing away from you, the bevel is farther on the right side than on the left side? This doesn't make sense to me considering that on a right-handed single beveled knife, the edge will be at 0.

do you mean higher up the blade?

[adletson]

A few questions:

1. When a knife is asymmetric, is it asymmetric from the spine down or just at the bevels? Or reworded, is it ground at dfferent angles the entire width of the blade from the spine down or is it just the bevel that is ground asymmetrically?

2. While I can see that the generalizing I made in my previous post is at fault, is the basic premise not correct? That in order to get an asymmetric result, you have to do different things to the two sides of the blade, either to grind less at the same angle as the matching side or to grind at a different angle than the matching side?

3. Continuing with my number line picture (1-2-3-4-5-6-7-8-9-10), on a "90/10 right hand ground" asymmetric knife, with the spine up, edge down, tip facing away from you, would the knife edge be at 2 or 9?

[heirkb]

do you mean higher up the blade?

No, I mean where the actual edge is relative to the spine. That is, where do the two bevels meet? My guess was 1, not 9.

[heirkb]

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.

So I have a few other questions here. What do you do to figure out the angle on that first side? I realize that practice is big, but I don't even know where to start, lol. You get the angle, flip the knife, and sharpen till burr? That will itself lead to asymmetric bevels (bigger on the right)?

And if you feel the blade twisting...let's say it twists towards the left while cutting on a right handed knife. The post above says you adjust by grinding more on one side or the other. So what side would you be grinding more on/making angle adjustments on if the knife steers a bit too much? That is, what type of improper sharpening does the steering suggest?

[Sarge]

So I have a few other questions here. What do you do to figure out the angle on that first side? I realize that practice is big, but I don't even know where to start, lol. You get the angle, flip the knife, and sharpen till burr? That will itself lead to asymmetric bevels (bigger on the right)?

And if you feel the blade twisting...let's say it twists towards the left while cutting on a right handed knife. The post above says you adjust by grinding more on one side or the other. So what side would you be grinding more on/making angle adjustments on if the knife steers a bit too much? That is, what type of improper sharpening does the steering suggest?

If you are right handed and the knife pulls toward your left hand when cutting you can either: grind more on the left hand side to even it up and bring it closer to 50/50. Or you can relax your grip some and not try to make the knife go somewhere but rather let the edge do the cutting for you. Either way you'll find that steering decreases

[zitangy]

Originally Posted by adletson

So am I correct in saying that when a knife is described as being "90/10 right hand ground" that it means that the cutting edge is 90% offset to the right side? Like if you had a number line (1-2-3-4-5-6-7-8-9-10) that represented the total width of the spine of the knife, the cutting edge is sitting on the 9th place holder?
yup

I think its the opposite???

My reasoning tells me that the offset is to the left as the right side has a higher bevel.. meaning that it has been sharpened at a lower angle. IF the the Left side is sharpened at Zero.. it is a single bevel. Since the left bevel is so small, it would mean that it it sharpened between 10 to 15degrees.. thus form the top of spine position it is anywhere between NO 2 or 3 as per your example

I suppose there should be a sharpening angle on the left side that makes it dead center of the spine. IF the total angle left and right is say 40 degrees.. close to the german sharpening way but with teh thinner bevel on the right side.. a thinner blade on the edge..

Just my thoughts...

rgds

[dbesed]

This is how i understand it :

http://i1060.photobucket.com/albums/t454/dbesed/grinds.png?t=1327837365

The right is the right side of a knife when you hold it in the hand. I think that Dave talks about picture 3.


Please corect me if i am wrong :sad0:

[Andrew H]

What I don't understand is why making the asymmetry on the bevel match the asymmetry on the blade face reduces steering. Say you have a 90/10 right hand bias blade face. Why would a 90/10 bevel steer less than a 50/50?

[Eamon Burke]

This is a subject that is very difficult to elucidate without massive amounts of diagrams & illustrations, or just sharpening and re-sharpening and extensively using different knives.

I am considering tackling this topic. But in the mean time, if you trust me at all, Dave is right.

[bieniek]

I want to understand just about the same thing. Massive lot of diagrams for me, please

[mano]

At the risk of appearing very stupid, in what way would using a magic marker along the edge work/not work here?

[Eamon Burke]

Assuming the knife was not altered from the appropriate bevels given by the maker, it would work just fine. As always.

If you screwed it up first, the marker trick won't guide you through repairing it.

[eto]

I have been dwelling and debating with this with myself for quite some time now. I get the whole thing that if you sharpen , say a knife that comes from a manufacture that is 70/30 , and sharpen to a almost 50/50 edge it will be just fine. The knives Im talking about are western style Gyutou's .

Im left handed and I have used knives set up for right hand use with little to no ill effect. Just the occasional blade feeling like its cutting towards the food as apposed to away from the food, depending on the product being cut. My question is are these knives ground throughout the entire blade from edge to spine with one side flat and one side sort of half a clam shell. For example HAMAGURI (convex) edge. If this is the case how would effect a knife for a person who is left handed and wants to set his edge's wider on the left side and less on the right side of the blade.

Especially if the user is a pro cook/chef who can reduce his knives entire profile from sharpening by many inches over say a period of 2 years of use. Will the knife still work once you start getting up into the blade. Hope this makes sense. Diagram below kind of show what im trying to explain.

http://www.zanmai-japan.com/img/topimg04.gif

[Seth]

Specific examples that some may know - just to get a little more clear on this.

So a KS: This knife is flat on the left side and convex on the right. In this case a large low/medium bevel on the right and low angle debur on the left is the best scenario? This puts the edge in position 2, let's say.

So a Shig: This knife is concave just below the spine, then flat, then convex on maybe the last 3/8". It appears to be more or less the same geometry on both sides. The best routine for this knife is likely a 50/50 equal?

Is this consistent with what Dave is explaining?

s.

[keithsaltydog]

I learned all my sharpening one on one wt. Japan trained Sushi Chefs.All freehand on the stones,double & triple blended bevels on Gyuto.Yanagi,deba,usuba,hollow ground single bevels,Cleavers I always use 50/50.Gyuto mostly assem,even turned a few into single bevels.

When I first saw Dave Martels DVD I learned why what I was doing worked.What he calls thinning behind the edge is the same as the blended bevels I've put on my carbon masamoto's many yrs.

This is how I learned assym. bevels,wt fingerpads press edge of blade till it bites a little into the stone,check your spine thats your edge contact angle if you want to blend lower the spine just a hair & work it till you get a burr.Flip the blade over & do the same thing.With a assem. blade when you press edge into stone the spine will be higher on cutting side & lower on backside.You do have to worry about degrees of angles just pay attention to the edge contact on stone & always keep a steady spine while sharpening.

Sound too simple?Well alot of it is some simple tricks as Dave said there is alot of diff. info. on sharpening,I have found Japan styles to be the best it's never failed me all these yrs.Since I first learned it 30 yrs ago Ive never had to use a dull knife,of coarse I only use carbons.Much of it is good tips & practice.The feel for the flow of steel on stone.

[Von blewitt]

Thanks Dave, Eamon and everyone else who had contributed to this thread. I have read, & re-read it, made notes and drawings and today put it into practice and was amazed, I've never got results like this before, I have an edge pro collecting dust but was reluctant to sell it off because I could not get consistent results free handing. I thinks it's time to move it on and make room for some new stones:)

[Zwiefel]

This is how i understand it :

http://i1060.photobucket.com/albums/t454/dbesed/grinds.png?t=1327837365

The right is the right side of a knife when you hold it in the hand. I think that Dave talks about picture 3.


Please corect me if i am wrong :sad0:

fantastic graphic...thank you!

I think I understand what Dave is promoting....either of the first or the last in this picture, right? Not the middle two.

I just don't understand why (like some of the others).

[Korin_Mari]

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..

Omg thank you. Yes, it is just an incredibly irresponsible solution to give people who just want to sharpen their knives. I have had so many people come up to me and tell me about their Edge Pro recently. I had no idea what it was, until I youtubed it. It looks silly and I wasn't sure if it actually worked, but you just answered by question.

Awesome post by the way!

[Dave Martell]

I'm always glad to hear someone agreeing with me.....LOL

Thanks Mari

[lanel]

Do you advocate steeling the 70/30 edge and if so what sort of steel do you reccommend?

[knyfeknerd]

Do you advocate steeling the 70/30 edge and if so what sort of steel do you reccommend?
First of all, it depends on what type of steel the knife is and what you are using as a honing rod. I only use steel rods for german knives/soft steels, etc.
When I do hone my knives that are 70/30 or any other asymmetric bevel, I use a ceramic rod. The most important thing is to adjust your honing angle to that of the edge. I sometimes will view my placement of the edge against the rod by looking at it from the top to begin. Just to make sure my angles are right.

[Yoni Lang]

Thanks Dave for this.. had a lot of questions and found this topic to answer a lot of them.. I feel over the past year or so I've complicated sharpening by not fully understanding the basics before moving onto some of the more advanced aspects of sharpening. Think I had a better grasp on sharpening when I was first being taught. This definitely steered me back on to the right track.. Still lots of questions though... Not sure where this thirst for sharpening knowledge has suddenly come from.. Maybe working with people with razors has opened my eyes to what an actual sharp knife is, or maybe it was when someone asked when the last time I sharpened my butter knife was.. :laugh:

[bieniek]

I made some HQ image of whats happening and I would ask you guys to opinionate

http://i1290.photobucket.com/albums/b525/bieniekoriginal/Beznbsptytu1420u_zps52cc84ca.jpg

So what we have here is a knife assymetrically ground be it Misono Swedish, but with a 50/50 same size and angle bevels on both sides.

My understanding is that

1. because of how the blade is ground, when cutting [a carrrot] the right side is trying to push the produce to the right hand side.
2. Because the bevel on left han side is significant it tries to push the whole blade to the right hand side, and wedging occurs.

?

[ThEoRy]

Ever try to cut a piece of wood with a circular saw between two supports? Don't do it! I can imagine this might be similar. Pressure from both sides of the product pressing into the blade causing the wedge perhaps?

[Dave Martell]

A member sent me the link to this video and after reviewing it I thought it warrants that I show it here in this thread.

The video demonstrates exactly what I was talking about when I mentioned how you have to be careful who you get your information from on this subject. Here we have a guided sharpening system salesman talking about his take on how to grind asymmetric knives. I find this demo all wrong - just wrong.

Besides the worst belt grinder technique seen on the interweb...

1. The knife being used IS NOT a Japanese asymmetric knife - it's a super market western made 50/50 clunker. You can't possibly demo this topic on a 50/50 ground knife!

2. He's "showing grinding at a constant angle" yet he's free handing which isn't "holding a constant angle" at all.

3. He talks about how grinding more from one side of the knife than the other is how you adjust the asymmetric ratios. This is true of coarse - but only if you're talking about skewing the ratio so bad that the f-ing knife steers, twists, and cleaves your food apart. This is so basic of an understanding to me that I'm stunned to see him make these comments and demo this in public.


So even though I don't believe in promoting this guys BS I'm posting this for everyone to see the exact opposite of what the REAL DEAL on asymmetry is.



http://www.youtube.com/watch?feature=player_embedded&v=dDsWh_M7Rek

[chinacats]

:surrendar:

[ThEoRy]

A member sent me the link to this video and after reviewing it I thought it warrants that I show it here in this thread.

The video demonstrates exactly what I was talking about when I mentioned how you have to be careful who you get your information from on this subject. Here we have a guided sharpening system salesman talking about his take on how to grind asymmetric knives. I find this demo all wrong - just wrong.

Besides the worst belt grinder technique seen on the interweb...

1. The knife being used IS NOT a Japanese asymmetric knife - it's a super market western made 50/50 clunker. You can't possibly demo this topic on a 50/50 ground knife!

2. He's "showing grinding at a constant angle" yet he's free handing which isn't "holding a constant angle" at all.

3. He talks about how grinding more from one side of the knife than the other is how you adjust the asymmetric ratios. This is true of coarse - but only if you're talking about skewing the ratio so bad that the f-ing knife steers, twists, and cleaves your food apart. This is so basic of an understanding to me that I'm stunned to see him make these comments and demo this in public.


So even though I don't believe in promoting this guys BS I'm posting this for everyone to see the exact opposite of what the REAL DEAL on asymmetry is.



http://www.youtube.com/watch?feature=player_embedded&v=dDsWh_M7Rek

"My name is Ken ******** and I'm going to show you the traditional way to sharpen a Japanese knife with this Target brand knife on a belt grinder..."

13389

[Dave Martell]

What he doesn't get, or address, is that it's not about making a choice to either grind more (from one side or the other) or change angles (on one side or the other) - it's about doing what the specific knife's edge requires (which might be a combination of both or whatever method) needed for each side (edge) to stay in relation to the blade's asymmetric shape.

[jayhay]

Wow, Kens voice is really annoying. I've never used a Burr-King, but do you really have the belt cut towards the knifes edge? Seems like it could grab the edge if you grind at too high of an angle, and shoot the blade at your body.

Amazing people even take the time to make videos like these.

[Yoni Lang]

Amazing people even take the time to make videos like these.
:doublethumbsup: agreed

[Slypig5000]

I read this this morning, I know it's not a j knife, but I have a 40 year old beater dexter that I resharpened to 80/20. Curious to see what this does for the knife.