As a woodworker sharpening is a never ending learning experience and challenge. My own approach to sharpening has changed dramatically since I first started woodworking. In particular since coming to Japan I have had the opportunity to learn from some very skilled people, and as a result my sharpening process has evolved quite a bit. I will confess that I had a fair amount of skepticism regarding all of the methods described below, when I first came to Japan. Many of these ideas were quite different from what I had learned as a carpenter using Japanese tools in the states. But after seeing the speed and results that could be achieved, it became harder and harder to argue that what my coworkers were doing was somehow wrong, especially considering they have been doing this a lot longer than myself.
As carpenters trying to make a living doing traditional work, speed is naturally of huge importance. If you’ve got a pile of posts and beams that all need to be hand planed, then you are going to have to sharpen your blade many times throughout the day, and the ability to quickly re-sharpen and get back to planing is crucial. One time soon after I started working here in Japan, I was planing posts for a new building with my boss Yamamoto-san. We were planing for a few days and naturally had to sharpen many times throughout the day. At the time I was sharpening in the same way that I had been for many years, using three stones (course/medium/fine), with a flat bevel (no hollow grinding, no double bevel). I could re-sharpen and get a pretty good edge but it could take anywhere from 10-15minutes. Yama-san in the meantime would hollow grind out his blades and put a double bevel on his blades on the finish stone. He could re-sharpen in just a few minutes and be able to take cleaner, better shavings than me.
So I started to incorporate hollow grinding and double-bevels into my sharpening routine. At the same time a friend and I have also been spending many hours in our free time experimenting with different stones and techniques to see how we can improve our sharpening and planing results. So what follows is a general overview of our techniques, as well as a brief description of some of the stages that have led to the technique I currently use.
Hollow Grinding
Hollow grinding is one of the more contentious topics when it comes to sharpening Japanese blades. Perhaps the biggest argument against grinding is that you can burn the edge of the blade, thereby changing the edges hardness and weakening it’s cutting ability. When I grind I keep a bucket of water next to the grinder and am constantly dipping the blade to keep it cool. If you are careful to keep the blade cool and keep from grinding right up to the edge then you should be safe from damaging the temper of the blade.
Another argument against grinding is that by hollowing out the soft iron that supports the hard steel cutting edge, there is a greater chance for the edge to chip or break. I’ve heard this theory get passed around many times, but I have to say that in practice this really hasn’t been the case for me, or to my knowledge my fellow carpenters who have been hollow grinding their blades for a very long time. We grind our chisels too, and I have spent days pounding away on hollow ground chisels and never had any chips or failures in the edge. The main benefit of hollow grinding is that it reduces the amount of steel that contacts the stone when you sharpen the bevel, making it much faster to sharpen right up to the edge. It also makes sharpening more stable.
Aesthetically one downside to grinding is that it’s ugly. Japanese blades often have beautiful layers in the softer iron (jigane – 地金), and if you hollow grind you obviously won’t be able to see those layers as you sharpen. However as a carpenter the ability to sharpen faster and effectively plane more wood seems more important to me than the aesthetics of the blade. After all it’s the finish planed surface that is the ultimate goal of all this.
The Double Bevel
A double bevel serves as a final measure to very quickly ensure the very edge of the blade has been sharpened. I was also skeptical of double bevels for years, thinking that doing so would make re-sharpening more laborious. But after trying double bevel sharpening, I really have not found it to be anymore difficult to re-sharpen, and my ability to very quickly achieve a sharp edge has improved immensely. When I first started playing around with double bevels I would use a microscope to compare a double beveled blade with a blade that was sharpened flat. It became clear that you don’t need a double bevel to get a really sharp edge, but it takes a lot longer to remove the scratches from the previous stone, than when you use a double bevel.
Two Stone Sharpening Method
One weekend my friend and I were experimenting to see how minimal we could make our sharpening process, and we started going from a very course 800 grit Bester stone straight to a double bevel on an 8000 Kitayama. Even with that huge jump from course to finish stone, a light double bevel on the Kitayama was able to remove the scratches from the course stone. With this technique we were getting better edges than if we went though a usual sharpening routine (course, medium, fine stones) in a fraction of the time. We even had several mini-kezurou-kai competitions to see how thin we could take our shavings using this method, and while we didn’t break any records we were consistently able to achieve 15 micron shavings, which is pretty good considering we were using 2 stones and spending just a couple of minutes for each sharpening! For months I continued to use this technique for sharpening and it was really effective.
Planing sugi
That said, a couple months ago I hit a wall with the two stone sharpening method when I was planing some sugi beams for a new building. Sugi is a notoriously difficult wood to plane. One piece of sugi might be a joy to plane, and come out smooth and glossy with little effort, but the next will be a complete nightmare, and you start to feel like you’re going insane because you can’t get a clean surface. There’s nothing like the challenge of planing woods like sugi or western red cedar to test your sharpening skills.
When planing woods like sugi or western red cedar your blade needs to be really sharp to get a smooth, clean surface, and you can typically only take a few clean shavings before the blade looses its’ ability to cut cleanly, even though the blade may still be quite sharp and could still plane other woods perfectly well.
While going from 800 to 8000 works pretty well on woods like hinoki, I was not having great results with that method on sugi (or at least it’s a bit more hit and miss). My guess is that with the 800/8000 method, if you’re not really careful it’s possible to miss some of the course stone scratches, leaving the blade a bit too rough for really soft woods. So after a bit more experimentation I realized that by starting on a much finer stone I could get a better edge, that would consistently cut cleaner on sugi. In particular I realized that since I was re-sharpening so frequently I could get away with starting on a much finer Hibiki 3000 stone and still quickly remove the double bevel. At the same time I also started experimenting with a super fine Naniwa 12000 finish stone for the double bevel and found that it really improved the sharpness of the edge, and the planed surface was noticeably better.
So lately I have switched to this method of using the 3000/8000/12000 series of stones. From time to time, if the edge is really worn I will jump down to a courser stone to start with but continue to use the 3000/8000/12000 sequence afterwards.
The blade below was sharpened using the 3000/8000/12000 process. You can see the hollow ground bevel, and the black line at the edge that is the double bevel.
I’ve been experiment with this process when planing hinoki as well, and it’s been really effective. Overall it may take a touch more time that the 800/8000 method I was previously using, but the result is a much more consistently sharp blade and it’s still very fast. I’m also really enjoying the 3000 Hibiki and 12000 Naniwa stones too. For a medium grit stone the 3000 really cuts fast making it easy to remove the double bevel and produce a slight burr on the ura side of the blade, yet the scratches are small making it quicker to remove them on the 8000/12000 stones. I also really love the Naniwa 12000 which gives an insanely sharp edge that makes planing a joy.
There’s a lot more to address when it comes to the ura side of the blade, but I think I’ll leave that for next time.
Happy planing.
Hi Jon
I loved this report, but have to confess I rarely take the time to sharpen up so rely on sandpaper to finish with. Shame!
One problem I have is that my good stones have names rather than grain size. I guess the internet might tell me.
Keep up the good work reported in your blogs. Thank you
Thanks Keith, I’m really glad you enjoyed reading. No problem with sharpening with sandpaper, plenty of people do it. But if you’re ever interested in figuring out what stones you have, let me know their names and I’d be happy to help you figure out what grit they are.
Best,
Jon
Thanks for sharing Jon! The world of sharpening seems never ending!! Hope to give this a try some day!
Thanks,
Dushane
Thanks Dushane! Let me know if you give it a try, I’d love to hear how it works out for you.
Best,
Jon
Great information! Thank you so much for sharing your knowledge!
Thanks Lisa! I’m glad you enjoyed reading.
Hello Jon,
Thank for for writing your blog. It is rare to get the perspective of someone actually in the Japanese woodworking trade.
I was confused at first, but what you call “double bevel”, is often referred to as a “micro bevel” in the popular woodworking literature. Double bevels more often refer to a bevel on both sides of the edge of a blade. Toshio Odate in his book “Japanese Woodworking Tools” writes about creating a micro bevel, but he advocates only one or two very light strokes, holding the end of the blade and drawing it backwards and up on the stone; to create a rounded or high angle micro bevel. He writes it is more to aid strengthening the edge, rather than ease of sharpening.
Can you clarify if you resharpen just the double bevel several times before regrinding?
Looking forward to more of your insights
-David
Hi David,
Thanks for your comments.
I understand what you are saying about difference double bevels vs micro bevels, and yes the techniques I laid out could be described as a micro bevel. My coworkers and I have all been experimenting with micro bevels a lot lately. We only do the micro bevel on a finish stone, and each of us has a slightly different technique. Some people may draw the blade back once or twice like Toshio Odate does, but I personally find the it’s not super effective that way. My technique involves working the micro bevel on a 12000 grit stone lightly working it back and for maybe 10 times or so (with a short stroke maybe around 20mm) and then lightly removing any burr from the ura side of the blade. I repeat that process three time and try to add lighter pressure each successive time. You can see that process in the video linked in the article.
I do think that Toshio Odate is correct that the micro bevel can make the edge stronger, simply because you are making the bevel angle steeper. I just played around with this the other day when I had a blade that had a very shallow bevel angle around 30 degrees and it was chattering and around knots when planing. After adding a steeper angle micro bevel the edge stopped flexing as much during planing and worked much better. The same holds true if you have a blade that is chipping during planing, if you steepen up the bevel it will likely chip less.
As far as resharpening goes, I almost always remove the micro bevel by sharpening the main bevel of the blade before putting the micro bevel back with the finish stone. If you keep the micro bevel very small removing it is really quite fast and easy. But if you continue to sharpen just the micro bevel, then obviously little by little it’s going to get bigger and will require a lot more effort to remove.
For me the micro bevel definitely makes sharpening faster and more consistent. Just yesterday I planed a cedar board during work and in 30 minutes had to sharpen my blade 4 times to get some really clean shavings. There was another carpenter next to me sharpening as well but in a more conventional way (no micro bevel). In that 30 minute period I was able to do some planing and resharpen 4 times, while he was sharpening the same blade throughout that whole period of time. I definitely find the micro bevel method to be very fast, and in the end allows me to do more planing which is what it’s all about.
I will try to illustrate this in a future blog post, but if you buy cheap pocket microscope and look at your edge while sharpening, I think some of these details can become more clear. In particular the speed of the micro bevel vs conventional sharpening. If you sharpen on a course stone and compare how long it takes to polish the edge between the micro bevel and sans-micro bevel under a microscope it becomes really obvious that the micro bevel can much more quickly remove the scratches from the course stone and produce a polished edge.
Thanks again for your comments, and let me know if you give any of this a try. I’d be interested to hear how it works out for you.
Best,
Jon
Hi Jon, I wanted to try the 12000 stone you mentioned, and was wondering if you had more details on the model. I see a kagayaki (goken-pro) and a super stone, and a tsuyoshiken. Hope you are well, enjoying all the extra writing lately, Brian
Hi Brian, I just looked it up and the one I’m currently using is Naniwa NK-2291 (gouken kagayaki). If you give it a try let me know how it works out for you. I find it moves a lot, though lately I haven’t been storing it in water and I wonder if that’s part of the problem. That said it’s fairly easy to lap flat. And the edge after doing a light double bevel on this stone is pretty sweet.
Take care,
Jon
Hi Jon
This has been really eye-opening. I do all my woodworking in our apartment and do not own a grinder. Nevertheless the double/micro bevel and curved ura has significantly speedened up my sharpening AND giving me more consistent results. I live in Denmark where we traditionally use alot of hard wood like oak, ash, elm and “hard” soft wood like larch, and i really think that the micro bevel improves the strenght of the quite brittle japanese steel when used on these woods.
Keep up the good work
Mathias
Hi Mathias,
Thanks for your comment, I’m really glad to hear you’re getting good results with this sharpening method. I agree that even without hollow grinding it’s still a fast and consistent sharpening style.
Best,
Jon
Hi Jon, I have been using your technique with sharpening and it has worked super well! I am a starting to feel a bit more confidence and interested in trying out the hollow grinding. Can you describe how often you are hollow grinding and performing ura – dashi? Any specific grit on the grinding wheel? In your video it looks like you just do a few passes on the grinder. It would be great to hear how often you are going back to the grinder and needing to perform ura- dashi. It has been really inspiring to see your work, especially in a professional design manor. (Ill be trying out your ha-ganna set up this summer!) – Mike
Hey Mike, Glad to hear you’re getting good results with the double bevel. The video is a bit misleading in terms of how long it shows me hollow grinding. The full length of that grinding session was a few minutes, but I edited it down in the video. I typically hit the grinder whenever the hollow disappears. I will do a bit of ura-dashi right after hollow grinding, since the hard hagane will often move a bit after grinding out the softer backing iron. After grinding I like to hit the ura on a stone to check if the hagane has moved or not. If it hasn’t I’ll skip ura-dashi and just keep sharpening. I’m not sure what grit wheel I have on the grinder, since I bought that grinder used with the wheel attached, but it feels like most standard 80 or 100 grit wheels. The important thing is that it’s pretty soft, so it stays relatively cool and doesn’t get clogged up easily. Thanks for your comment, and looking forward to hearing how your ha-ganna setup goes!
Hi Jon,
a big thank you from France, I just discover your blog and you share really usefull information and beautifull work. I’m a retired carpenter and have been sharpening for the last 40 years, mostly on japanese stones, and I totally agree with your hollow grinding and double bevel. That’s how most joiners have been sharpening in Europe and it really speeds up the game. I restore a lot of old woodworking tools, european and japanese and it’s really fast. I agree with you, the only downside is it’s ugly, but if you want to have a usable tool fast , starting from an old rusty piece of steel, this technique beats them all. I guess the technique you use for kanna doesn’t apply to nomi and the longuest part of restoring japanee nomi is making flate the ura side. Diamond stones have been a real game changer for this part, I’ve been using kanaban before but find it real slow and I ‘ve been recently trying ura grinding on the Tormek and the results are greats but slow and ugly!
Thanks and pleasure to keep reading from you.
François
Hi François,
Thanks for the comment. I’m really glad to hear you’re enjoying my blog. And it’s also good to hear that as a professional woodworker yourself you’ve been using a similar sharpening technique. It really is effective and allows a person to quickly get a good edge and get back to planing.
As for chisels I do hollow grind and double bevel my chisels, but as you guessed my approach on the back of the chisel is a little different, and simply flatten the back of my chisels. I’ve had good luck using a kanaban by rubbing a very course 700 grit stone on the surface to create a course grit slurry, then a fair amount of pressure for pretty quick flattening. That technique has worked well for me, but diamond stones are also a great option as you mentioned.
Ura grinding on the tormek sounds interesting. Are you using any kind of jig or just hand holding the chisel? Finding a clean way to restore the ura is one thing that I’m still searching for. There are lots of different approaches but all are somewhat ugly as you said. So far the best option here in Japan is to send blades back to the blacksmith and have them do it! The result is really great, but obviously costs a bit of money.
-Jon
Hi Jon,
thanks for your answer, about tormek, I’ve got an old small model with 200mm wheel, I just rounded the outside corner and do all my sharpening freehand. I’ve seen on videos that japanese smiths use a lot of different diameters and shapes wheels to grind the ura, well obviously you can’t grind all chisel shapes on the tormek! and it’s slow but with no chance of steel burning. I used to grind an ura on my french carpentry chisels with an hand held grinder and a lot of water cooling, the result was ok but I was always afraid of burning! Do you have an idea of the price of grinding in Japan, I was thinking of maybe sending my best chisel I dare not grind on the tormek?
Thanks
François
Hi François,
I haven’t ever sent any planes or chisels out for ura work so I can’t really give an accurate price, but a friend who was planning to do it told me it might cost around $50 per blade. That said I think a lot will depend on the condition of the tool itself, and the level of work involved. Sorry I can’t offer much more info than that at the moment.
Best,
Jon
Hi Jon,
thanks for your answer, with the price of postage and taxes so high now I guess it would be cheaper to buy a new nomi than sending it to Japan for grinding! I will keep practising my ura grindind and ura dashi skills for the moment!
Best
François
so nice to read, a lot of good information, thanks very much
Tiu
Hi Jon, I’m interested to know the diameter of the grinding wheel you use for hollow grinding. I have a 10″ (about 250 mm) wheel that seems too shallow to get a hollow grind without accidentally grinding the blade edge. Also the speed of the grinding wheel in rpm’s.
I’ve been reading your posts a lot lately as I’m getting back into sharpening hand tools for a project and finding what you have displayed and written very helpful.
Many thanks,
Eric
Hey Eric,
In the video from this post I used a grinder with a pretty small diameter wheel, somewhere around 4.5 to 5 inches. I used a small diameter grinder like that for a long time, and the nice thing is that the hollow becomes quite deep and will last through several sharpenings. The downside is that since more material from the soft backing iron is removed, sometimes after regrinding the hollow, pressure can be released and the hard steel will move, requiring that you tap out the blade (ura-dashi).
Lately I’ve been using a tormek to hollow my blades, and just like you described with your 10″ wheel, the hollow is very shallow. But I’ve also found I don’t have to do as much ura-dashi either. Recently I did a lot of planing for a project and each time I sharpened, I quickly hollow ground the blade on the tormek (free hand/no jigs), and then proceeded to my stones. The hollow sometimes completely disappears after one sharpening, but I still find it beneficial nonetheless.
Best,
Jon