Hello and welcome back to my blog. In this series I will be preparing a Kanna (Japanese hand plane) for upcoming work. I have planned to build shoji along with its latticework, kumiko. Kumiko is made up of many small pieces of wood cut to very exacting standards. In order to cut those pieces to an exact thickness the material is planed with a specialized kanna called the Hikouki Kanna, which is basically a plane with skis that ride along a special made track.
Wood, when made especially thin, can no longer support the force placed upon it during planing and result is that it will bow during the work. To counteract these forces the specialized Hikouki Kanna features a bamboo pressure bar which applies a force on the material ahead of the blade to keep that material flat. This, along with a flat supporting track, will allow the material to be cut cleanly. The Hikouki kanna has a second specialized feature in which its runners can be adjusted to size the material to a desired dimension, removing the need to mark and check thickness as the work is being processed.
I begin with a new kanna and dai. Lucky enough I stumbled upon a Nakano kanna with a dai cut by Inomoto-san. The blade, made of Hitachi white steel 1, should be able to take an incredibly keen edge so long as it is prepared correctly. A sharp blade with a very flat edge is so potentially critical to the ultimate result that I decided to detail the processes of preparing a new plane blade.
I start preparing the blade by working the back, called the ura, to create a flat perimeter around the urasuki (hollow). Japanese plane blades are made from very hard steel and so to be able to maintain a flat back, the blacksmith will grind a hollow (Urasuki) into the back. The outside perimeter (Uraba and Ashi) is ground flat by the blacksmith and then maintained by the user for the life of the blade. Good maintenance starts with good prep.
I begin this process by checking the blade on a true flat surface for teeter-totter. Where the blade pivots are high spots.
These high spots, if one were to simply start abrading the back, would create an uneven ura and therefore much embarrassment whenever I show photos online. I adjust this by first working the back on my anvil using shims and a wooden drift pin. The back of the blade, constructed of soft iron, can be made to deform slightly which will then deform the hard steel back. Now I can’t go ahead and beat on the hard steel….that would not do well, so I use a wooden drift and apply force to the center of the back. With shims at the low corners I will ‘adjust’ until the blade sits flat without teeter-totter.
The blade now sits flat, still I am not ready to grind away carefree on the ura. I preparing a 1000 grit synthetic stone for the work by flattening it and checking it to ensure it is flat with a precision straight edge. In preparation the stone has been soaked in water, which can affect its flatness.
My next step is to begin ura-oshi by lightly working the back on the stone.
As an aside I feel it is important to understand that synthetic whetstones literally go out of flat as you use them, so as soon as the show steel particles on their surface I will stop to resurface them flat again with an Atoma diamond plate. Maintaining consistently a flat surface will allow my results to be reliable.
Now I can clearly see where contact is being made and where it is not being made. There is an area along the center of the uraba which is not contacting the stone, now if I were to continue then all areas of the flat would begin to grow in size, except this area, making for an uneven ura.
To remedy this I use a process called ura-dashi, or ‘tapping-out’. During this process the soft iron of the blade is deformed to then move the hard steel while utilizing a rounded corner of an anvil or similar as a backer. It’s very critical not to hit the hard steel or lower half of the bevel near the hard steel which would break the blade.
Now I go back and forth between ura-oshi and ura-dashi until the full perimeter of the ura contacts the stone evenly, noted by an even scratch pattern.
Next I move onto the 3000 grit stone, similarly prepared, but change the direction at which I hone very slightly so that I can see when the 1000 grit marks have been removed.
Followed by 8000 grit.
And the resulting ura.
Maybe you are wondering….but where are the Jnats! They are to follow, but first I grind the bevel. I begin work on the bevel with a rough stone because removing the marks from ura-dashi takes some effort, and the areas tapped out are now showing as low spots on the bevel.
The bevel is hardly flat at this point, mostly because the low grit synthetic stones, while fast cutters, go out of flat very quickly. So rather than continue with synthetics I move to oil stones to make the bevel very flat. Oil stones retain their flatness very well, even in low grits and so for a blade where flatness is critical they certainly shine.
Flatness starts at the roughest grit, as you move up in grit it becomes seemingly easy to lose flatness but significantly harder to improve it after it is lost.
It’s critical to keep an eye out for inconsistencies, to highlight low spots I change the direction in which I’m honing. I change it just enough so that the scratch pattern of each stone is able to be distinguished from the prior grit. In the photo below, I’m pointing out a section which is low.
Next I work up through to a soft Arkansas stone. The finish on the bevel is quite nice at this point.
Finally I can move onto the Jnats, the Tsushima stone dishes with relative ease, so I start with the Yaginoshima asagi which is a stone that does not dish easily, then move onto the Shinden suita and finally the Nakayama asagi. I repeat this same series on the ura.
I check for flatness with a straight edge in both directions.
Finally, I strop the blade on a clean cordovan strop and now I can move on to the chip breaker.
I begin a similar process on the chip breaker, however, first checking the chip breaker’s fit against the plane blade and adjusting the ears to suit.
The chipper goes through the same process of ura-oshi and ura-dashi, then the bevel is worked flat.
I follow this by standing the chip breaker up on the stone and grinding a very small microbevel of about 70 degrees.
And the resulting microbevel.
That’s all for now, in the next post I will begin fitting the blade into the kanna dai.
I owe a debt of gratitude to Chris Hall, So Yamashita, Stan Covington and David Weaver whose insights and guidance are boundless and thoroughly appreciated.
Hope you have enjoyed reading, please comment below!
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