Kanna Workshop – Dai Adjustment Tools

Unlike western style planes which are tuned to be perfectly flat and don’t require maintenance save for the occassional touchup, the sole of a kanna dai gets very slightly hollowed out, reducing the areas of contact usually down to just 2 points, and preserving that condition requires frequent maintenance.

How often a kanna dai needs to be touched up really depends on the size of the dai, the type of work being done, and the surrounding envirnment, ie. changes in humidity. A longer and wider dai will react much more to changes in humidity than a smaller one and tends to require more frequent touch-ups. Also fine finish planing demands a more finely tuned kanna than rough planing, and likewise will need more frequent adjustment to keep the tool in prime planing condition. In other words when it comes to larger dai and finely tuned finish planes, subtle changes to the bottom of the dai can result in poor planing, so frequent checking and adjustment becomes necessary.

There are a few different tools and methods for maintaining kanna, and I tend to use a mix of all of them in my own work. The main tools I use include a 15 mm thick glass lapping plate with some 120 grit adhesive sandpaper attached; a tachi-ganna or dai-naoshi-ganna (立鉋、台直し鉋); a razor blade scraper; straightedge; and of course a mallet for setting the blade in the dai.

Sanding Plate

The tool I probably use the most for adjusting my kanna is the glass sanding plate. Depending on who you ask, sanding the bottom of a kanna is kind of a contentious topic. Some people swear that you’ll end up embedding sanding grit in the dai which will break loose as you plane and ultimately end up damaging the edge of your blade. I don’t deny that is a possibility, but I’ve personally never run into that problem so long as I make sure to clean off the dai after sanding, usually by blowing the sanding dust off with an air compressor and and perhaps a quick wipe from a clean/dry rag. I also frequently follow the sanding plate with a scraper, which also helps to clear away stray sanding grit.

The big benefit to using a sanding plate is that it’s super simple to remove any potential twist from your dai. Subtle twist in a dai can be hard to diagnose, but will definitely make planing more difficult. I’ve often run into issues where a plane just isn’t cutting right, and even if things look mostly okay when checking with a straightedge, something seems to be causing the plane to cut poorly. A quick reset of the sole of the dai with the sanding plate usually solves the issue.

While dai-naoshi-ganna and scrapers allow you to adjust a dai with the blade protruding, obviously that’s not really an option when using a sanding plate. And to complicate things further, a dai with the blade fully removed can have a very different condition from one with the blade tapped in for planing. Since the blade is wedged into the dai, tension is introduced which usually manifests itself more obviously behind the blade as the dai’s bed gets pushed down. Sanding a dai without the blade will result in a nice flat dai, but as soon as you tap in the blade there will often be a buldge in the area behind the blade. So using a sanding plate usually requires some follow up adjustment with either a dai-naoshi-ganna or scraper as well.

My strategy when using the sanding plate is to insert the blade part way, usually pushing it in as far as it will go by hand, but making sure it’s plenty clear from running in to any sandpaper. Having the blade inserted at least part way allows you to get much closer to the final goal. I’ve also started to use the sanding block to sand out the hollow as well, by turning the dai sideways and sanding away the areas that I want to hollow out a bit. This works really well, you just need to be mindful of not sanding the flat contact areas that you want to maintain.

Dai-naoshi-ganna / Tachi-ganna

Next up, the dai-naoshi-ganna (some people call them tachi-ganna). These are kanna made for maintaining your other kanna. The blade is held vertically turning it into a scraper plane which allows for delicate removal of material and adjustments to the bottom of your kanna dai. I use mine along with a simple little fence which is really helpful when adjusting the material closest to the blade.

Final adjustments to a kanna are best done when the blade is tapped out to the same level it will be used, so when using a tool like a dai-naoshi-ganna, you need to be really careful to avoid hitting the main blade, and a fence can be helpful for that. I use my fence for guiding the dai-naoshi-ganna when cutting behind and in front of the blade, setting the fence on the dai as you see below.

One side of the fence is extended to give me a visual reminder of where the blade of the dai-naoshi-ganna ends.

Then I can set the fence on my kanna and be sure that I’m clear of running into the main blade.

Scraper

The last adjustment tool that I frequently use is a scraper. This is a scraper that I made, copying a design from Yamamoto-san at Somakosha. The blade is an Olfa long snap-off utility blade, held in a wood body and secured by a simple wedge which causes the sides of the holder to clamp down on the blade. I really love this tool. It’s such a simple and cool design, and it works really well. The blades are also cheap and can be easily resharpened much like a standard scraper blade.

Most of the time I reach for the scraper more than the dai-naoshi-ganna. The scraper is really effective at removing material and making fine adjustments, and it’s less cumbersome to use than a dai-naoshi-ganna. Also the wide flat blade makes it easy to consistently and evenly remove material from the dai.

I’m working on a video showing these tools in action and had hoped to include that in this weeks post, but it’s taking me longer than anticipated to do all the editing. So stay tuned for that. In the meantime here’s a quick video showing the details of the scraper and a quick shot of it in action.