Sharpening Kanna : An Evolving Method Part 5

This past summer I spent three months in Okayama working with Somakosha on prep work for a couple of overseas projects. During that time I also took a month to work on a furniture project for a client of my own using Somakosha’s shop (more on that in a future post). I ended up doing a lot of hand planing over that three month period. It was a really interesting mix of wood. I had the opportunity to plane plenty of soft wood like sugi (Japanese cedar) and hinoki, but also planed quite a bit of douglas fir, some Japanese red pine, and a type of Japanese hemlock called toga (栂). My own project was a furniture piece done in white oak. So all in all it was a good learning experience planing a range of wood species each with very different characteristics.

Despite the differences between all those wood species I essentially used the same sharpening method (micro-bevel) for everything that I planed, with a few minor variations here and there. Below are a few observations from that intensive period of planing.

Dealing with Chippy blades

My collection of planes has grown quite a bit since coming to Japan, and it’s been really fun to play around with a variety of blades. One thing I’ve noticed is that some blades are much more prone to micro-chipping during sharpening than others. In my usual sharpening routine I often sharpen the bevel on a course stone, and then jump up to an 8000 stone and start working on a micro-bevel. After the micro bevel I always hit the ura side of the blade to work back any burr that has formed. With certain blades I often end up with a bunch of micro-chips along the edge. It’s not necessarily something you can see with your naked eye, but under a pocket microscope it’s quite clear. My guess is that the burr is breaking off when I hit the blade on the ura side on the 8000 stone, resulting in an edge that looks jagged.

In those situations something that I have found helpful is to go minimal when sharpening on the coarse stone. Using a 1000 grit stone, I have been working the bevel just enough to almost remove the micro-bevel from the previous sharpening session. If you look at the edge in a good light or under a microscope you can still see a faint polished line at the edge; the remaining sliver of the previous micro-bevel. The result is you stop short of forming a burr. From there I proceed as usual to 8000 and 12,000 grit stones.

By holding back a bit and leaving a touch of the previous micro bevel, I’ve had much better luck getting really clean edges particularly on blades that are prone to micro chipping.

Another technique that has been working well for dealing with chippy edges, is to use a lot of pressure on the finish stone. On numerous occasions I have checked the edge after sharpening on the 8000 stone, only to find that the edge was still jagged, and full of little micro-chips. I found if I hit the micro-bevel one more time, using a decent amount of pressure, I could really easily and quickly remove the micro-chips and get a clean edge.

Planing White Oak

Below is a sharpening video taken while I was busy planing lots of white oak for a furniture project. I played around with a few different planes but ended up using a 60 mm Ishido kanna the most. There is a lot more resistance when pulling a plane on wood like oak. I found the narrow size was much easier to pull than a full size 70mm kanna. This particular Ishido kanna is also really easy to sharpen, and doesn’t seem too sensitive to micro-chipping. So I was able to start with a really course 700 grit Bester stone for quick re-sharpening sessions. I also found the wear on the edge of the blade was much heavier when planing the white oak and found the Bester could really quickly knock back any excessive wear. The Bester stone cuts really quick so it’s easy to form a burr, but the Ishido Swedish steel blade didn’t seem to be too negatively affected.

Using water when planing

Folks in Japan often wipe the surface of the wood with a wet rag just prior to planing. The water helps to push out dents and milling marks, but it also can improve planing performance as well. In particular it makes planing really difficult woods like sugi much more manageable. Recently I had one particular piece of sugi, that I couldn’t get a clean finish on. I could take one or two clean passes, but then the shavings always started to get fuzzy, leaving a rough surface. I resharpened a bunch of times, doing my best to get as sharp of an edge as I could, but I just couldn’t get a consistently smooth finish. One of my buddies came along and basically poured water on the surface, ran his plane over the board and was able to get a beautiful glossy surface.

The topic of using water during planing could become a blog post of it’s own. To be honest I’m not 100% sure about everything that is going on when you plane a wet surface. But talking to the folks I work with, there are a couple of running theories. One theory is that the water helps to keep the blade cool, allowing the sharp edge to last longer before being worn down by friction and heat. Another theory, that I think has the most impact, has more to do with how water affects the cellular structure of wood. With really soft woods like sugi or western red cedar, the summer grain fibers are floppy and weak when dry. By adding a little water, the weak summer grain will soak up the water filling the cells, giving the weak fibers some structural support, thus allowing you to cleanly plane the wood.

The downside of using water is that it can cause your dai (wooden plane body) to move. Some people try to counteract dai movement by either oiling or sealing the dai with some type of finish. Nonetheless sometimes dai movement is a problem, and sometimes it’s not. Another potential negative effect is that water can also cause the piece your planing to move, depending on it’s thickness.

For those reasons I have been hesitant and skeptical of using water, but I’ve also witnessed how much it can make planing really difficult soft woods much more manageable, and produce amazing results.

Sharpening and planing is a constant challenge. The more I play around the more I realize there is more to learn. I’m finding it more and more difficult to draw hard line rules. When people ask questions about sharpening most of the time I feel like the answer is “It depends.” Each person has their own unique method and style of sharpening and planing. And each blade, and each piece of wood has it’s own character which gets mixed into the equation. All together there are a ridiculous number of factors involved. I think what’s important is to find a system that is enjoyable, and from there just sharpen and plane like crazy. See what works and see what doesn’t. It can definitely be frustrating at times but when things go well, there is nothing quite like the experience of taking thin shavings and seeing the wood shine.