Hello and welcome back to my blog. In this series I will be preparing a Kanna (Japanese hand plane) for upcoming work. The kanna, by Nakano with a dai cut by Inomoto-san is newly made but not quite ready for use. High quality preparation of this blade, made of Hitachi white steel 1, will allow it to take an incredibly keen edge. I’ve created this post to help demystify the process of kanna prep by detailing the steps I take in preparing a new blade for its long life planing wood.
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. To allow the maintenance of a flat back the blacksmith will grind a hollow (Urasuki) into the back. The blacksmith flattens the outside perimeter (Uraba and Ashi) which is 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. I can deform the back of the blade, constructed of soft iron, 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. Instead, I use a wooden drift and I 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.
(1/2020 update: I now do this process as depicted in On Ura-Dashi: Ito-Ura) using ura-dashi and a fine stone a neater ura can be made.
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 see an area along the center of the uraba which is not contacting the stone. 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’. I perform this process by tapping, with a hammer, the soft iron of this blade. It’s very critical not to hit the hard steel or lower half of the bevel nearest 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 to the 3000 grit stone.
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. Removing the marks formed by ura-dashi takes some effort.
The bevel is hardly flat at this point, mostly because the low grit synthetic stones, while fast cutters, go out of flat very quickly. The stones which progress after this point will help to make the bevel progressively flatter. Starting with an 800 grit stone I will flatten the bevel and remove the convexity created by a rougher stone.
Maintaining flatness starts at the roughest grit. As I progress to finer stones, loosing flatness becomes seemingly easier and regaining it significantly harder.
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 the angle enough with each grit so that the scratch pattern of each stone is distinguishable. In the photo below, I’m pointing out a section which is low.
Next I work up through to a 3000 grit synthetic. The finish on the bevel is quite nice at this point.
Finally I can move onto the Jnats. Starting 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.
I begin a similar process on the chip breaker. First I check the fit against the plane blade and adjust to suit.
I process the chipper using ura-oshi and ura-dashi, as I did the iron, then I work the bevel flat.
Next, I follow this by standing the chip breaker up on the stone. I then grind a very small microbevel at 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. The insight they have provided me is both boundless and greatly appreciate.
I hope you have enjoyed reading, please comment below!