Kanna curious?

In learning more about woodworking it doesn’t take long before one comes across someone professing as to the virtues of Japanese tools – in particular chisels and hand planes. In a previous post, I focused a bit on Japanese chisels, which I think have broader penetrance into the western woodworking world. The Japanese wooden hand plane, called a kanna, seems a bit more mysterious to the western woodworker.  

In browsing the internet to find out about these Japanese variants of a hand plane. There are a couple of things that one quickly learns:

1. Some people really like them, almost fanatical about them. They have assembled groups that obsess about how to get the finest shaving from them – something like 0.0001” 
2. Because the body of the plane is made out of some exotic Japanese wood, they are finicky to get set up and sharpen.
3. They seem expensive especially if you buy new. Some of them seem to cost thousands of dollars.

So let’s try to address some of these misconceptions first and then let’s talk about what you should consider when trying to get one to work.

First, wooden planes are awesome. Instead of listing all of the ways that you refuse to use one (“I won’t use one planing oak, I won’t use them in a boat.”) just go ahead and try one. They have advantages over metal-bodies planes in that they are typically lighter and they also have better steel in the blades. The Japanese kanna is a type of wooden hand plane. As I mention in a previous blog post, the western variety largely stopped production in the mid-1800’s due to the emergence of metal hand planes produced by industrial processes. In contrast, the wooden hand plane continued to evolve in Japan.

One of the key differences between wooden-bodied and all metal hand planes is in the blade. The wooden hand plane has a blade forged by a blacksmith from hard high-carbon and “soft” low-carbon steel. The laminated design takes advantage of the working properties of these two different types of steel. In the context of wooden hand planes, the advantage of the Japanese hand plane over the western hand plane is that the blades in contemporary Japanese hand planes leverage more recent knowledge of metallurgy. In contrast, the western wooden plane largely uses steels produced in the 1800’s. Encouraged by the Americans Joseph M. Juran and W. Edwards Deming, Japan led the world following World War II in improving the quality of industrial processes, like steelmaking. Blacksmiths, like Shigeyoshi Iwasaki, were at the forefront of incorporating these newest steels into their tools. Blacksmiths also assembled into guilds, like the Tokyo Chisel Cooperative and Tokyo Plane Association, to share this knowledge. So wouldn’t you want to use more contemporary materials than based on 1800’s technology in your tools?

Regarding the perceived fanaticism out there, yes, there are organizations, like Kezurou-kai, that celebrate the skill associated with using a wooden Japanese hand plane. They organize “shaving contests” where the person that shaves the thinnest shaving from a really nice grained piece of cedar wins the contest. While this may seem a bit fanatical, the contest also brings together people to exchange expertise in sharpening and kanna preparation related to the contest and helps elevate the knowledge base in the entire community. For most practical purposes, you don’t need to set up your plane to take sub-thousandths of an inch shavings but it is important to know what you need to do to get it to work. These shaving clubs are not dissimilar to clubs that we have in the US for kids to make robots to navigate obstacle courses – sure the particular challenge seems a bit silly but you have to learn a lot to be able to compete. 

Using a hand plane to shape and smooth wood is an important skill of any woodworker. Yes, these tasks can be done with power tools but the entry point to do a particular task can be quite expensive. The entry point with hand tools can be considerably lower. The steps that one takes in converting rough planks of wood into furniture is also different if one takes a path that relies predominantly on hand tools versus the power-tool route. The hand-tool route is one of pre-industrial craftsmanship, which the folks over at Mortise & Tenon and Lost Art Press are trying to help modern day craftsman to rediscover. In terms of the hand plane, the design and configuration of the hand plane can be slightly different depending on where you are in the process of converting a rough plane to finely finished wooden surface. A great article summarizing the difference is Christopher Schwarz’s article on hand planes titled Course, Medium, & Fine.  

Regarding Japanese hand planes being finicky is, in my view, a bit based on impressions based on the volume of interpersonal exchange rather than woodworking practice. In short, hand plane work follows the Pareto principle in that 80% of your work should be with hand planes of the course and medium variety and only the last 20% of effort should be with the fine variety. Moreover, your effort in setting up a course and medium variety hand plane should only take 20% of your effort while setting up a hand plane for fine work should take 80% of your effort. This is why there is a lot of interpersonal exchange about setting up Japanese hand planes to take fine shavings. You can go this route of using a hand plane from start to finish if you want. However you can get pretty close to a finish surface without become too obsessive about the performance of your fine hand plane. Worst case, there is the random orbital sander, which would be the final step if you didn’t use hand planes anyway. Setting up a hand plane to work well for that last say 5% takes some refinement of your skill.

Expense and Experiential Learning

Ok so these arguments have piqued your interest in Japanese hand planes. Woodworking, though, is an activity that vicariously experiencing a Japanese hand plane through either words or video just doesn’t cut it. You have to try it out yourself. But how would one try a Japanese hand plane because they are not sold at your neighborhood tool store (i.e., the big box store). In browsing the internet, you find that new Japanese hand planes sold by reputable tool resellers can be quite expensive. That is not surprising considering that it is still a largely hand-made product with the blade made by a blacksmith and the wooden body made by someone else.  While there are cheaper new “Japanese kanna” out there, I would not recommend them. An alternative route would be to buy a used Japanese hand plane. Due to a combination of cultural tendencies and demographic trends, used Japanese hand planes can be obtained relatively cheaply. Similarly, wooden western planes can be found in certain parts of the US relatively cheaply.

So then how then does one bring back a used Auction find into a usable state? Just like when you take a used car into a mechanic, they have a checklist to assess what needs to be done to make sure that this used car is safe and reliable. So let’s create a checklist to assess the state of a used Japanese hand plane.

First a bit about Kanna anatomy;

The Japanese kanna is comprised of at least two parts but many cases has four parts. The first two are the blade and the wooden body, called a dai. The second two parts are the secondary blade, or chipbreaker, and the pin that holds the chipbreaker in contact with the primary blade. In the following sections, I’ve grouped the checklist into points to consider for each part of a kanna. 

If you obtain a kanna from a different part of the world, one of the first things to do is to remove the blade from the dai soon after arrival because the atmospheric moisture content can be different than were the plane body originated. The shrinking of the plane body in width around a blade that doesn’t shrink can cause the back-end of the plane body to split, if it already hasn’t.

The Blade

• Remove rust from the blade. Some of this is aesthetics but rust on the hard steel layer particularly on the blade back (or ura) can lead to problems later at the cutting edge.
• Remove / smooth mushrooming of the top of the blade head due to use of a metal hammer in adjusting the plane blade. Use of a plane adjusting hammer that is made using materials softer than the plane blade will minimize this effect going forward.
• Is the cutting edge square to the center axis of the blade? The design of the blade is roughly an isosceles trapezoid with an axis of symmetry down the middle. As the cutting edge is the narrowest edge, this creates a wedge that tightens when the cutting edge projected out of the bottom of the plane. The corresponding slots in the plane body is cut to match this wedge shape with some additional space so that the projection of the blade can be adjusted slightly by tapping on the side of the blade. When the cutting edge is deviates too far from being square to the center axis of the blade, the plane does not cut evenly across the cutting edge. 
• Is the back of the blade flat and touching a reference surface all along the backside of the blade tip? If not, maybe tap-out the bevel of the blade to lower parts of the back to contact the reference surface. This process is called uradashi.
• Is the bevel angle of the blade tip correct? Should be around 28-30 degrees. 
• Are mimi appropriate? Of note, the picture above doesn’t show mimi cut into the corners of the blade. Depending on whether you are using a chipbreaker or not, these should be such that the cutting edge is not inside the grooves on the side of the plane body. If you have a chipbreaker, the cutting edge should be narrower than the chipbreaker. (Chris Hall has a nice discussion of the set-up of a chipbreaker in his book).
• Are the backsides of the mimi softened? If not, this will in time degrade the upper surface of the side groove in the dai loosening the fit.

The Plane Body (Dai)

• Are there large splits in the dai particularly in back of the blade? If so, it’s time for a new dai.
• Are there small splits in the dai around the mouth opening? If so, you can stabilize small splits around the mouth using thin superglue.
• Is the bottom out of wind? How is the grain run-out on the dai? Answering these questions will help determine what kind of plane this is meant to be – a course one or a fine one?
• Is the mouth opening small enough for the intended use (course, medium or fine)?
• Is the mouth ledge (Tsutsumi) intact? If no, then remove it.
• Is there about a 1mm gap between the side of the blade and dai side groove?
• Is the top reference edge of the side groove flat? If not, this may mean a new dai. 
• Is the blade held in the dai too loose? – shim with paper / hide glue 
• Is the blade held in the dai too tight or the blade doesn’t project out of the mouth after about 5 solid taps to seat the blade? Adjust the dai with file/chisel to promote contact around perimeter of sides and bottom. Here is blog post by Wilbur Pan describing how he does this.
• Is the dai too thin? Could add more to the bottom by laminating on a new bottom.
• Does the bottom have the appropriate points of contact (2 or 3 PoCs)? If no, relieve bottom in between desired points of contact. See Toshio Odate’s article in American Woodworker (Sept 1993) for a more detailed discussion of these points of contact.

The Chipbreaker and Cross-bar

• Is the chipbreaker needed for the type of use (course, medium, or fine)? If no, remove chipbreaker and bar to simplify plane and skip the rest.
• If yes, is the cross-bar usable? Is it straight, close enough, solidly attached?
• Does the chipbreaker fit in the dai width-wise? You can check without the blade being in.
• Is the backside of the chipbreaker flat?
• Is the bevel angle correct? It should be about 60deg.
• Does the chipbreaker lie flat on the blade? 
• Does the chipbreaker slide in fairly easily over top of the installed blade with hammer help only the last couple of mm?
• When installed over top of the blade, does it have contact with the crossbar in the middle?

Based on your assessment of the used kanna in regard to it’s four parts and it’s intended use within the course/medium/fine hand plane paradigm, we can then plan a strategy to rescue this kanna from the discard pile to become an effective tool in your woodworking arsenal. In a future post, I will go through a couple of case studies. 

References

• Toshio Odate “Japanese Woodworking Tools: Their Tradition, Spirit, and Use” Linden Publishing (1998)
• Chris Hall “The Art of Japanese Carpentry Supplement Kanna: Japanese Plane Set Up, Tuning and Use” Copyright 2018 and available at https://thecarpentryway.blog/2016/12/tajcd-supplement-plane-set-up-and-tuning-now-available/
• Dale Brotherton “Sharpening and the Japanese Hand Plane in Depth” Copyright 2017 and available from https://japanesecarpentry.com/wordpress/product/book-sharpening-and-the-japanese-hand-plane-in-depth/
• Scott Wynn “Discovering Japanese Handplanes” Fox Chapel Publishing (2017)