Sharpening a Japanese (grind) Style knife (unsymmetric 70:30)?

[aquataur]

Greetings,

I am in the verge of upgrading my cooking utensils with a Japanese Knife.
Edit: knife information updated.

As different to most of that league offered in Europe, that one, although being a double edged knife,  is ground asymmetrically at an unknown percentage.

This site (and others) recommends for sharpening:

If the double-edged kitchen knife is a symmetrical 50-50 V-shape, you will apply a similar number of strokes on both the front and the backside of the blade. However, if the front face has more edge than the backside such as in a 70:30 double-bevel kitchen knife, you will apply 7 strokes at the front and 3 strokes on the knife's backside.

This approach suggests equal angles on both sides, but on some other web page I have seen actual different angles specified for the respective sides (unless this procedure results in different angles, which I fail to comprehend).

The shop on the beginning mentions (in the blog somewhere) that the grind can of course be overridden with a standard 50/50 grind, but they surely have had some intention with that. (That said, it may not make a big difference.)
Edit: they have...

Masahiro's edge is its most important feature. The edge is 80/20 asymmetrical, rather than sharpened equally on both sides. The idea being that the asymmetrical edge is 35% thinner than a 50/50 edge. This fact makes Masahiro's knives sharper than other Japanese knife brands.

(Source)

We have learned that a primitive knife jig or a wrongly clamped knife will produce such a non-symmetry, albeit as an unwanted side-effect and probably vastly unpredictable let alone controllable.

Does anybody here have experience with such knives? Has anybody worked out a solution other than nerve-wrecking re-adjustments on tasks like de-burring? I found no reference to this neither here nor there.

Thanks,
Helmut

[aquataur]

So far I found out about Japanese knives:

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.

(thread #1)

He mentiones that he does not know the reason for this.

and also

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.

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.

• 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.

I do not know how credible the guy is, but he seems to be appreciated, and his arguments are plausible.

So this clearly phases out the koiknives recommendation from my preceding post for sharpening so many strokes to each side. Darn. This would have been easy to accomplish on the Tormek.

What the guy says about EdgePro certainly applies to any guided (wet-) grinder.
This means individual angles for each side.
This further means, better steer clear of such knives?

He says that virtually all Japanese knife-makers produce asymmetric knives - unless they were specifically determined for the Western market. Japanese technology in a European package...

Maybe stick to those...

[cbwx34]

I've found Dave to be very credible over the years... so much so that...

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... he had some good examples in the (now gone) Knifeforums, showing that with most Japanese knives, the entire knife is ground asymmetric, not just the cutting edge.  It's what I've found in the few Japanese knives I've done.  I think they're best sharpened on a flat stone, (but that doesn't mean they can't be done other ways).  I did "play around" with touching up a Japanese knife with the SJ wheel, and it can be done, but like I've said elsewhere, you're adapting the knife to the sharpening method.  (A "purist" would probably never do it?)

KnifeGrinders posted a video on sharpening Japanese knives on the Tormek... so it's an option.  (It's for single bevel, but gives an idea of how to do it.)

I found this on Misono knives that indicate they're sharpened at different angles...

Generally, Japanese kitchen knives are designed for right hand use with a slightly thicker and rounded grinding on the right side blade and a less rounded (almost straight flat) grinding on the left side blade. Misono produces 100% left handed version with suitable blade grind angle and edge geometry from the beginning process.

Link

... and not the same angle on each side, with one side sharpened "more" than the other.

Of course some of it depends on the knife user's skill level too.

[3D Anvil]

This is where it pays to have a goniometer, so you can measure the edge angle on both sides.  Assuming they're different, and you want to maintain that, there are a couple of approaches you could take.  One would be to adjust the projection distance from one side to the other and the other would be to adjust the USB height.  Shouldn't be a huge deal if you minimize the number of times you switch sides, i.e., don't switch until you have a full burr on the first side.

[Ken S]

For a different point of view, start at 21 minutes on this online class with the T1. (The same would apply with the T2.)

https://www.youtube.com/live/nqD0cefN0yU?feature=share

Ken

[tgbto]

A good ally in this adventure will be a magnifying device.

I have two such knives. The thinner one has the same edge on both sides, the other doesn't. A good way to know would be the following : use the Sharpie trick on the widest bevel, flip it once you get your angle right, then do it on the other side. Use the microscope/magnifier to check if the angle needs to be adjusted or not.

A few additional ideas :
- You might want to use "BevelCalc" in @jvh's TormekCalc spreadsheet or similar to measure the factory angle with a reasonable precision/confidence, and save it for future reference. I'd do it with the knife straight out of the box, I find it much more precise than a goniometer, and cheaper. I do it with the KJ jig in order to minimize jig-induced assymetry.
- You can also make a note of how many graduations on the MicroAdjust nut you have to adjust by when switching sides if your angle is different, so you can alternate between sides, instead of doing one side and then the other, as with the SVM-00 where the angle is always slightly off.
- Advice such as x passes on one side then y on the other to preserve the x:y ratio have to be taken with a grain of salt... Many parameters will vary, including the grinding pressure which will be higher on the shorter edge. So the idea will be to do what is necessary to preserve the edge geometry, eyeballing and lots of care may be required. Here again the magnifier will come in handy.

[aquataur]

Well thanks for the inspirations so far.

I did know neither Dave Martell nor the forum that he wrote the article in until recently. Although he writes with confidence, I had not way of determining the truth in his words. Hence the reluctance...

I know the KnifeGrinder video. He only grinds one side. The facet is quite prominent, so IIRC he wanted a straight facet and not a hollow cut. I think a facet this size and that acute would not be possible on the circumference without hitting the jig.  But in fact this is how I thin my knives behind the cutting bevel. There is ways to true the side...

I am not sure how to use bevelcalc to reverse-engineer the geometry. I would be thankful for help here.

The knife I bought has the following shape (see attached file. source: A Basic Explanation of Asymmetry

note the drawing is much exaggerated. Kippington gives us an explanation for making a knife asymmetric from the start.

Interestingly, the knife maker recommends a symmetric grind at some low angle.

The shop that sold it to me thought that the knife is so tough that it hardly needs to be sharpened (Dave has said it...) but it will at some point.
A clad knife is tough, but not invincible.

The cutting facet is really small, maybe 1/2 mm on both sides, and it seems symmetric as far as I can tell. According to Dave, it should have asymmetric cutting facets, but I cannot tell the knife is steering to any side. With repeated grinding back the problem may arise (Kippington explains this in post#25) and then a firm knowledge of the original shape is needed. However, I can see that it only takes some very light touch-up with a japanese stone of sorts, and that can be done the traditional fashion.

So maybe we should leave it at that for the moment, until further wisdom arises.
Thanks,
-Helmut

[tgbto]

I am not sure how to use bevelcalc to reverse-engineer the geometry. I would be thankful for help here.

There :

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This spreadsheet is a jewel Measure the diameter of your wheel, projection distance and TUSB when you're satisfied with the setup for the sharpie trick on either side. Use the "Top of USB to wheel", not the others so you don't compound measurement errors. Then read the angle in the bottom cells.

You won't be exact to 1/10th of a degree, but that should do. Especially if you use the same method for setting up your angle in the future, as you'll at least be consistent in the way you take your measurements.

[aquataur]

Thank you tgbto,

I realize that I had the right notion about this program. It is the same geometry applied backwards compared to TormekCalc´s other program parts.

However, I do not have the MS Office programs needed to run it. The progam itself is absolutely reasonable, but not the Office part. Moreover I dislike the new style they introduced intensely.
It does not run on libreoffice.

But it´s easy enough to use Angle Calculator Lite and look up the table it generates. Instead of choosing a grinding angle and a projection value to look up a corresponding T-USB value one can choose a projection value and the measured T-USB value and look left for the corresponding grinding angle.

Of course one could modify the table to reflect this, but that appears overkill.

[cbwx34]

Calcapp has a similar calculator...

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... look under the menu "Specialized Calculators" "What is the Angle?"

 

[tgbto]

Nice, a reasonably precise goniometer for the price of a paire of calipers

[aquataur]

very nice, thanks.

[Ken S]

My single bevel experience goes back to when I had a photographic side business. Part of the business was custom mat cutting. The most precise blades for cutting mats were single edge. As an experiment, I purchased two inexpensive santoku knives. I sharpened one with the traditional double bevel. The second knife was sharpened with only one bevel on the left side. I am left handed. This knife worked very well for me when cutting cheese. It tracked very accurately. I put the project aside, as the difference did not seem significant to me. If my cooking skills were more advanced, I might have pursued the tests more, including trying out different angles on both sides.

I notice drawings showing one bevel being convex. With a little practice, the KJ-45 should be ideal for this work

Ken

[aquataur]

That is interesting.
I wanted to quantify the geometry of my knife, but it is very hard with me old eyes despite all distorting magnifying glasses.

The blade is very thin and asymmetric, but somewhat rounded with no sharp transitions between the bevels, so it is not easy to put a finger on things. It is asymmetric, that is for certain.

I notice drawings showing one bevel being convex. With a little practice, the KJ-45 should be ideal for this work

Actually, both bevels are convex, just not as much. For right handed knifes the right side is more convex to aid food release. Unfortunately this creates more pressure there that by tendency steers the knife left. Hence the prominent grind on the left side for compensation.
That is what is reported anyways.

[tgbto]

I notice drawings showing one bevel being convex. With a little practice, the KJ-45 should be ideal for this work

I doubt it, because you won't be able to reproduce the initial convexity as the KJ-45 constrains you to use whatever range of angles the distance between the two stops chooses for you. Moreover, it will be very hard to be even remotely precise on the side where the short edge is. I have only tried to convex knives with the KJ-45 for a few hours, but I find it is a lot of effort for a result that is very, very far from what you get with a belt sharpener where you can play with slack or belt stiffness.