September 09, 2021 5 min read 0 Comments
Sharpening kitchen knives is a fun hobby, one that gets you more in tune with your tools and teaches you a handy skill. There are many ways to do it right, and it's okay to make a few mistakes along the way. Sharpening single bevel knives, however, is a more challenging task that requires a careful approach. In this blog I will explain the basic techniques and tips that you need to follow to start sharpening your own single bevel knives!
When you are sharpening single bevel knives, such as a Yanagiba, Deba, or Usuba, there are definite right ways and definite wrong ways of doing it. If you sharpen single bevel knives the wrong way, not only will the knife not get as sharp as it should, but you can also ruin the knife. My goal is to help you avoid those outcomes and have a beautiful sharp knife at the end of the process!
Now that I've really built it up for you, I'm gonna let you in on a secret: single bevel knife sharpening is pretty simple. All you need to do is to follow the shape of the bevel that is already there. What causes problems is when they are sharpened like a regular Western-style knife. Let me explain how it works:
As you can see, the knife is made with two different types of steel: one softer and one harder. Hard steel is is used for the edge, while soft steel protects the hard steel from breaking. The "back" side of the knife is called the Urasuki, which is the concave section that helps food release, and the Uraoshi which are tiny flat areas that run along the top and bottom of the Urasuki. The Kireha is the main bevel on the opposite side of the knife, making it a single bevel knife.
When you sharpen single bevel knives, you want to sharpen the Kireha and Uraoshi flat on the stone, spending most of the time grinding the Kireha so you don't remove too much of the hard steel or flatten the Uraoshi. Then, on the last finishing stone you put a Koba, or micro bevel, on the Kireha side. The Koba is like the hem on fabric, it makes the edge stronger. When you sharpen the Kireha you want to make sure the Shinogi line at the top of the bevel remains nice and straight. The width of the Kireha stays the same as as you sharpen. What this means, is that the Shinogi should move up the knife at the same rate that you remove steel from the edge. See the diagram below.
The width of the Uraoshi should not exceed 2mm or so. If you sharpen the Uraoshi too much, you shorten the life of the knife by removing too much of the steel that forms the edge. The concave area, the Urasuki, has 2 functions: to create an air pocket so that food does not stick to the blade, and to make the knife easier to sharpen The steel on the back of the knife is quite hard, and having less surface area means you need to remove much less steel when sharpening.
In addition to using good technique, being patient, and taking your time, it is very important to keep your stones flat when sharpening single bevel knives. This helps you maintain a consistent Kireha and Uraoshi.
In a nutshell, the technique is as such: Starting on your flat coarse stone, sharpen the whole Kireha consistently until you raise a burr. Flip the knife over and sharpen briefly on the back side to remove the burr. Progress through your preferred selection of stones, flattening each before using them, repeating this technique and bringing the bevel to your preferred level of polish. Once you're on your final stone, put the Kireha up a few extra degrees and add a koba. Polish on your leather strop and you're good to go!
This section is to illustrate the work required to repair an improperly sharpened single bevel. As you will see, it is a very long and arduous process, one that I don’t recommend home sharpeners attempt.
Sometimes, customers bring single bevel knives into the shop for repair that have been sharpened like a normal Western-style double bevel knife from both sides, instead of following the Kireha or Uraoshi. Repairing knives damaged this way is quite challenging, even for a very experienced sharpener like me, and can take many hours to accomplish. I'll say it again: I don't recommend doing this yourself unless you have a lot of sharpening experience. That said, if you were to fix one, this is how I do it.
If a knife is sharpened like this too often, it can ruin the knife forever. As mentioned above, these knives are made with two different hardnesses of steel and the softer steel will not take or hold a good edge. If a single bevel knife is sharpened like this for too long, the softer steel will soon get to the edge and ruin the whole knife.
First, I need to get the Uraoshi back. To do this, I place the knife flat on its back and grind the hard steel until the inside beveled part of the edge is gone. Because the back side is all hard steel, this is a long, arduous process.
Then to make it easier to maintain in the future, I made a new Urasuki. In the past I have done this using unconventional tools, and it was very challenging. I do not recommend home sharpeners attempt this, this should be done by professional knife makers only.
The Kireha bevel was also sharpened at the wrong angle, so I removed a great deal of steel from the front side of the knife and made the bevel more acute. You can see in the above diagram how much steel needed to be removed to accomplish this.
While repairing knives like this teaches us an awful lot about how to repair single bevel knives, we would rather not see knives come in like this in the first place. What we do recommend for folks interested in sharpening their own single bevels is to take their time, use high quality stones, and contact us any time they're having trouble.If you’re still learning about sharpening and need to learn conventional knife sharpening, we also offer a standardSharpening Class where beginners can start learning the art of knife sharpening.
GlossaryHagane: harder, edge steel
Jigane: softer, protective steel
Kireha: the flat part from the Shinogi line to the edge
Koba: micro bevel. Usually hair thin.
Shinogi: the line where the bevel starts.
Uraoshi: the small flat parts on the back (<2mm)
Urasuki: the concave part on the back
Naoto came to Canada in 2007 and we aren't letting him go back. After getting angry with his roommate's dull knives, he started to dream of sharp Japanese knives. Naoto graduated from the University of Calgary with a bachelor degree of art, majoring International Relations and finds that selling Japanese knives is his own way of doing international relations. Naoto is our Cultural Ambassador bridging Japan and Canada. You can also see him in SpringHammer looking cool and holding it all together.