DISCLAIMER: The video above was published on YouTube by Trace Study. The video is part of an amazing series of videos featuring prof. Kenji Komatsu from Toyama University teaching about the setting and maintenance of a Japanese plane (kanna). I do not own, nor I claim, any rights on these videos - all copyrights are owned by the respective owners.
The following is a non-literal translation that I have made, with my wife's help, to better understand prof. Komatsu's teachings. I am publishing this translation for the only purpose of sharing it with the woodworking community, hoping that this can be of help for other people as well. If you know of any ways to improve this translation, please feel free to contact me. Any contribution will be of great help to the whole community.
Uragane: sharpening and adjustment
How to sharpen uragane and how to make uradashi
Let’s see how to sharpen the main bevel of the uragane and the smaller secondary bevel.
Before we do that, as we have seen for the main blade we need to perform uradashi. Using a fine diamond plate we check. We could also use the plate with powder as we have seen before.
Now that it’s nice and flat we can finish with the polishing stone.
Now it’s perfectly clean all the way to the corners.
How to sharpen the bevels
Now we sharpen the main bevel. We take a regular stone. The first bevel should be sharpened at 25 degrees. It seems a very sharp angle, doesn't it? Let's see why.
If it weren't this sharp it wouldn't allow the shaving to come through the mouth nicely. If it weren’t this sharp it would get stuck in the mouth of the plane. This part of the mouth needs to be open. Therefore this needs to be a very sharp angle to be able to leave space in the mouth for the shaving to come out.
Now i finished the first bevel at 25 degrees (some books suggest to use an even sharper angle)ow we need to add the second bevel. Looking at the model, we can see that we need to sharpen the main bevel first, and then the secondary bevel afterwards.
Then the uragane is placed on the back of the blade and moved forward or backward. When the blade is moved forward for rough cutting, the uragane is moved backward. When the blade is moved backward for finishing cut, the uragane is moved closer to the edge of the blade. This is how you adjust the uragane in relation to the position of the blade,
The degrees of the secondary bevel vary according to different books. The majority of books say that it should be between 55 and 60 degrees some say between 50 and 60 degrees. Others say around 80 degrees. The secondary bevel should end up being 0.3 mm from where the tip would be without bevel. In my experience, this is good for finishing, but for rough cut i prefer to have a bigger bevel like this one.
This one we are working on, we will make it at 0.3mm and 80 degrees.
How to sharpen the secondary bevel
The main bevel was at 25 degrees. Now we raise it somewhere between 60 and 80 degrees for the secondary bevel.
This is 0.3mm. The shining part, you see?
Now on the polishing stone. The first bevel is not used for cutting so it’s not too important but we polish it anyways.
And now let’s do the secondary bevel. Obviously you will get a burr that you need to remove. And then we repeat. This is how you hold it.
This is how you do it.
Sharpening the corners
We are almost done, but since some people sharpen the blade giving it a little curvature, in that case the sharp corners of the uragane would protrude. In that case we need to remove the corners of the uragane as well. Rounding over just a little bit. Then on the finishing stone.
You can see it’s a little rounded.
So when we put them together, they are both slightly curved.
How to stabilize the uragane
If we touch here, we don’t hear much of a sound. This means that the edges of the uragane and of the kanna-mi are in perfect contact. We can adjust this by adjusting the two mimi (back corners of the uragane).
On this side you can’t hear any sound. But on this side you can hear a little rattling sound. When I press here, the other side raises up. Now these two are touching, so this side can move. This corner is too high (doesn’t touch) so we can either hammer this mimi down or file the other corner.
Let’s file a little bit from the other corner.
We can still hear a bit of rattling sound.
Now it’s good.
Setting of uragane and kanna-mi
The uragane and the kanna-mi should be inserted in the dai (the body of the kanna) together. You need to avoid that either one slides forward too much on its own while inserting them.
If the blade goes first and the uragane is added afterwards, the edge of the uragane will scrape along the back of the blade and this will round over the edge of the uragane. This is because it slides up from the inner rougher part of the ura, to the edge, and this causes rounding.
It’s very easy to ruin this edge.
When the kanna-mi and the uragane are inserted in the dai, it is possible that only one side of the uragane touches the pin (osae-bo).
Like this. On one side there is some space, on the other it touches. If this happens, the uragane will tend to shift around when inserted.
Ideally we want the pin to touch all along the uragane. In this case we can file the pin to ensure contact everywhere.
First you take the pin out. The pin original shape is a round section. So you file it lightly like this. Then you insert the blade and the chip breaker to test.
Now it fits perfectly. The uragane and the osae-bo must fit together.
Adjustment for kanna types
This kanna has a curved blade. In this case both the uragane and the blade are curved.
Same thing for this one, where the uragane and the blade have the same shape.