For kanna to work well the quality of fit between the blade and dai is cruicial. When you buy a new kanna the blade will need to be carefully fit to the dai by gradually removing materail from the bed of the dai until the blade seats firmly in the dai, and can be tapped in/out and adjusted using a hammer. The fit of the blade in the dai needs to be not too loose, but not too tight either. Overall the aim is to have the dai firmly hold the blade such that it doesn’t move/shift when planing, but not soo tightly held that it’s a bear to tap the blade in/out, or worse so tight that you actually split the dai itself.
I think I’ll cover the overall process of fitting a blade in another post, but for the moment will cover some of the overall areas of importance when fitting a blade to a dai.
Also kanna are unique tools in that the user ultimately has fully control over the fit and finish of the tool. So naturally each person has their own personal inclinations regarding what works for them. The following is my personal approach which has evolved over several years of setting up and using kanna, and which has definitely been influenced by a variety of other craftspeople.
Blade/Dai Contact
In general when setting up a kanna the areas of contact between the dai and the blade that are most important are the areas directly opposite the grooves in the side of the dai, and the area along the bottom of the bed close to the blade’s bevel and edge. The area I’m referring to is roughly highlighted in the picture below.
The area in the center of the bed is usually slightly hollowed out to prevent any contact between the dai and blade which can negatively affect the fit and function of a kanna in a few different ways. Contact with the middle can do some weird things to a kanna by creating unneccessary pressure in the dai; it can twist or push the center of the blade upwared; and it can create a pivot point that makes adjusting the blade a challenge. All of those problems make it harder to get good consistent shavings. By slighting hollowing out the center of the bed you can reduce unwanted issues and focus the fit on the areas that really matter.
The areas along the sides are important contact areas since that is ultimately where the blade will be wedging itself in as you tap the blade into the dai. Kanna blades are wedged shaped, and the further you tap in the blade the tighter the fit becomes. So having good contact along the sides of the blade ensures that the blade will be held firmly once it’s wedged in and seated. The line of contact across the bottom is important for giving support to the blade as the forces from shaving wood want to push the blade back. When this area isn’t well supported a common issue that pops up when planing is chatter, as the blade flexes back and forth from the force of planing.
Below is a shot of the same kanna above without the highlighted area. This is a kanna that I set up a little too loose and during the humid summer months here in Japan as the dai expanded the fit loosened even more. So I tightened up the fit using a bit of epoxy, which is the slightly darker U-shaped area that loosely follows the ideal areas of contact mentioned above. The dark patches are roughly the areas where the blade is contacting the dai, with the focus again on the areas directly opposit the grooves in the sides of the dai, and the area that supports the blade during cutting. A few stray areas of contact such as those on the upper end of the bed aren’t the end of the world, and sometimes these aren’t really true contact areas anyhow, rather they are simply rubbing points from inserting and removing the blade.
Here’s a smaller 42mm kanna. This is a daily user for me, and one of my go to planes when doing furniture work. The same concept regarding the ideals areas of contact apply to smaller kanna like this one. And on this dai you can see the shiny burnished areas where the blade and dai touch. The right side of the bed opposite the right hand groove is also burnished it just didn’t show up from this camera angle.
Blade/Dai Tightness
How tight a blade should be in a dai is perhaps the area where I’ve seen the most varied opinions among Japanese woodworkers. Again a balanced approach is essential. Too tight a fit and you can end up flexing the blade or actually splitting the dai, not to mention that the plane will simply be a PITA to adjust. But too loose is no good either.
I’ve gradually moved towards setting up my kanna looser and looser. And part of that is due to the fact that I use a wooden mallet for adjusting my planes. Wooden mallets have less enertia than metal ones, which makes a tightly fit blade a bit more challenging to adjust, while the same plane may adjust really easily with a more massive steel or brass hammer.
Ultimately I like to set up my kanna such that I can push the blade in with hand pressure and have the blade firmly seat itslef about 2 mm from the mouth, as you can see below. From here the blade gets tapped the rest of the way using a mallet, I’ve found that this rough distance makes for a blade that wedges itself tightly in place, but is still easy to adjust.
And here’s a similar fit on my smaller 42 mm kanna.
That’s it for this week. I had planned to go a bit deeper in this post, but time got away from me this week, so I’ll follow up with more next time.
To be continued…
