Sharpening Japanese knives

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This is a new subject for me, as I was gifted an Aritsugu Wakogoro knife by my sister in return for sharpening her kitchen knives. She and her mate were in Japan on vacation and she found an outlet shop where you’d buy knives and they’d sharpen them for you as you waited. She warned me to be careful, as it was VERY sharp! I chuckled, thinking of the times I’d warned others the same way.

When I got the knife home, I clamped it in my WE vise so I could examine the edge with my USB microscope. I have small pieces of UHMW tape on the face of my 'scope, so I can slide it easily along the edges of knives I sharpen. I was stunned to see that the edge would bite aggressively into the UHMW, making it difficult to do much sliding. In short order, the UHMW had been cut completely through, requiring immediate replacement. VERY sharp!

https://tcmeyer.smugmug.com/Knife-Stuff/i-Xg5zvzQ

I then went on youtube, looking for Aritsugu Wakogoro and found a video of an Aritsugu shop in Kyoto which seemed to match my sister’s description. She confirmed that this was indeed the shop she visited.

https://www.youtube.com/watch?v=Cdwd98EadAQ

On inspection with the 'scope, you can see that there are two separate grind lines along the edge. Of course, they are convex in form. The first grind pattern is longitudinal to the blade. The video shows this being done on a wide-faced drum-type wheel. The craftsman holds the blade horizontally at the very top of the wheel, moving the blade back and forth, while making contact only at the same tangent point. This seems to me to be very clever, as he can see plainly that he’s holding it at the correct angle. In fact, he’s probably varying the angle slightly to form the convex profile.

From the there, the blade is moved to a craftsman (maybe the same guy?) who works the blade on a flat waterstone to put the final edge on it. I should look more closely at the blade, as there may be a microbevel at the very edge.

Once the blade is sharp, it is handed off to an engraver, who engraves your name (or whatever else you might deem appropriate) in kanji characters on the back side of the blade. Mine says “Meyer” or whatever the engraver wanted to insult me with as I’ll probably never really know . The engraving is quite deep and from the video the steel is apparently quite soft, which begs the question; How hard is the edge?

So far, the only thing I’ve tried to slice with it is a hard section of Johnsonville Summer Sausage (I’m only about six miles from the Johnsonville plant). Pretty impressive! Woohoo!

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Great post, Tom! As you probably know I’m a lover of Japanese kitchen knives and I own quite a few. I’ve always wondered how these knives are sharpened at the shops: by machine or by hand. Your video shows that, at least for Aritsugu, it’s done with both. I don’t know if you can see it with your microscope, but I’d be interested to see whether the final edge (by hand) is a continuation of the edge made with the wheel or a micro-bevel.

This is really interesting, because even most higher-end shops I know sharpen their knives purely using a powered device (although the knife is guided by the hand). I’ve seen this myself in Laguiole, and there are some videos on Youtube that show how Chris Reeve has his knives sharpened this way. I encounter very little videos where the final finishing is done purely by hand, without a powered device.

There are great variations in the sharpness of Japanese knives out of the box. Most come very sharp, but some others come almost blunt out of the box. The idea seems to be that the user is supposed to put an edge to his own liking on the knife. And there are great variations in the quality as well: micro-burrs, chips, very uneven grinds, I’ve seen them all. Quite often the first thing I do to a Japanese knife is to put my own edge on it. But if it already has a great edge (Konosuke, Suisin, Masakage - and apparently Aritsugu too - are brands that usually have this) I can really admire it.

Oh and what is UHMW tape? I googled it, of course, but still couldn’t find out what it main feature is.

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Congrats Tom!! That is sweet… would love to see scope pics of the edge itself!

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I clamped up the Aritsugu in my WE vise and did some more serious inspecting of the edge today. As I said earlier, there are two readily apparent grind lines; the first running lengthwise and the other pretty much perpendicular to the edge, although it has some more random grind lines - maybe circular?

I have two photos for you here, showing both sides of the knife as it’s mounted in the vise. The photo in my opening post was compressed too much - sorry 'bout that.

https://photos.smugmug.com/Knife-Stuff/i-gP5zSr3/0/S/Aritsugu%20Left%20Side-S.jpg

https://photos.smugmug.com/Knife-Stuff/i-nKrqPrr/0/M/Aritsugu%20Right%20Side-M.jpg

The lengthwise grind (done on the wheel) is about 5 or 6 mm wide, while the edge grind is maybe 2 to 3 mm wide.

On the video, I tried to slide along the side of the edge grind to show the separate grind marks. You’ll see that there are a plethora of what we would call defects all along the edge. I tried to roll the camera over the edge to let you view the defects from several angles. To the extent that you can, note the keenness of the edge. When viewed edge-on, you really don’t see any bevel shoulders as we do with our edges. As near as I could tell with my best angle-cube, even with the convex profile, the included angle at the edge is only about 12 degrees. Woohoo! You’ll also note that these “defects” don’t seem to appear to be anything but sharp. I think that this is because the very low included angle leaves a foil-like edge, which may be worked by the slurry of the waterstones used. I tried to measure the included angle of a straight razor I have and it appeared to be 14 degrees.

The strands of white debris in the video are slices of UHMW the edge has stolen from my camera,

https://www.youtube.com/watch?v=96vWJ4hDW4k

Josh & Mark: I’ll be very interested in your comments!

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I think you’re pretty much right in your description, Tom. The knife clearly has two bevels. Whether the second bevel would classify as a microbevel, I don’t know; it seems a bit too large for that (but then again, that depends on your definition of a microbevel).

There are indeed quite a few defects along the edge. But given the fact that you’re looking through a microscope, they don’t seem too bad to me. Some of them might even be dust. I don’t see any major micro chips or a burr, or I must miss something.

 

 

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Cool knife and video! I’m really interested to hear how the edge holds up to extended use. What is the steel?

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Mark: The side I scanned in the video doesn’t show it very well, but on the other side, I think I see a different line along the edge, maybe only a few microns wide, which is what I thought may be a micro bevel. The video might show it partly at the points where I roll the camera over to the opposite side. I’ll have to crank up the magnification to get a better look at it.

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Thanks, Clay. I haven’t even thought about actually putting to use, as I don’t have the waterstones needed to touch it up. From the enclosed flyer, I infer that the steel is high-carbon non-stainless.

AS I recall, Josh mounted his Tormek small knife adapter in his WE Low Angle Adapter and was able to get down to less than 7 dps. I’ve bought a bunch of cheap kitchen knives from some of the local good-will-type stores and was thinking that maybe I’ll try to replicate the 12 degree included edge on one of those.

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Here is an image that might explain how they can harden a blade and still be able to engrave the sides:

http://ep.yimg.com/ay/chefknivestogo/sukenari-honyaki-white-1-gyuto-240mm-118.png

Either they use a torch or they have a forge into which they can insert only part of the blade.

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In Germany they have a nice term for describing a knife with a proper very thin edge: Nagelgängig. Coincidentally a thread was just started about this on a kitchen knife forum: http://www.kitchenknifeforums.com/showthread.php/23670-looking-for-english-term?highlight=nagel

The idea is that you run your nail across the edge which should then slightly deform, but get back into form when the nail is gone. I’m curious whether this edge is “Nagelgängig”. It indeed looks very thin and like Clay I’m also curious how it holds up in daily use. Personally I’d give it a try, but I think that in practice a microbevel might be a good idea. Obviously it depends a lot on the steel and the hardness.

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I watched one of these “How It’s Made” episodes in which they showed the production of traditional straight razors at the Solingen plant. One of the final steps was to press the edge flat against the fellow’s thumbnail (it could be that he used his ring - I don’t remember clearly). The edge was thin enough if the edge would flex under the pressure applied. To be clear,there is no attempt to touch the nail with the sharp edge or to “run your nail across the edge.” The test was to check for thinness and flexibility.

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Here is that particular episode.

https://www.youtube.com/watch?v=_b_nRYltQ-Y

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This knife is good for shaving, but not for kitchen. You can slice tomatos with it, but nothing harder than tomatos.