葉鉋　Ha-Ganna : Sharpening 1

So far in my limited experience playing around with ha-ganna, sharpening has been one of the more challenging aspects. Initial setup requires a few time consuming tasks, such as cutting and shaping stones for each blade, and tuning the edge so that it cuts at the right angle. In addition to get a clean cut the edge needs to be really wicked sharp. (This last part is one that I’ve been having particular difficulty with on my 60 degree ha-ganna.) So I thought I would share what I can regarding my approach to sharpening ha-ganna. I’m definitely not an expert when it comes to these planes, and a lot of this is new to me, but there is so little info available about ha-ganna that I feel like it’s worthwhile to share none-the-less.

Ha-ganna Sharpening Stones

Ha-ganna require specialty stones for sharpening. While the bevel side of the blade can be sharpened using a standard flat stone, the inside (ura-side) requires stones that are shaped to match the angle of each blade. No stones are readily available for purchase, so for each ha-ganna blade you need to make your own set of stones. Below are the course and fine stones that I shaped for each of my four ha-ganna blades.

To make the stones above, I bought a King 1000 course stone, and a Kita-yama 8000 finishing stone and cut each up into four parts. I chose these stones because they are pretty cheap, but also quite soft and easy to shape. Once I shaped a 1000 Shapton stone for use with a round kanna blade. Compared to a King the Shapton was a pretty hard stone, and it took forever to shape. I highly recommend soft stones for this task.

After cutting the stones into smaller parts I shaped each on a diamond lapping plate. Slowly grinding away while frequently holding the blade to the stone to check that I was making the shape the correct angle.

Once the stones were ready I lapped each blade on the course stone until I had an even flat area of contact across the cutting edge. Since the stones are soft you need to frequently touch them up on the lapping plate to keep them flat and maintain the correct shape. Once I had an even area of contact from the course stone, I repeated the same process using the finish stones.

Blade Geometry

The geometry between the angle of the blade itself (as it’s been forged), the bedding angle of the blade in the dai, and the angle of the cutting edge all play a role in what kind of angle you will end up with after cutting your kumiko. Since you can’t really change the blade bedding angle or the blade angle itself, to achieve an accurate cut, everything comes down to the cutting angle. To clarify, the following two images show the different angles I’m talking about.

By altering the blade cutting angle, you can adjust what angle results when cutting your kumiko.

First Test Cuts

After sharpening each ha-ganna, I took a few test cuts to see where things were at. Below are shots from the test cuts for the 45 degree ha-ganna. As I was cutting I could feel the plane pulling away from the surface of the wood. It turned out that the back side of the bevel was hitting the wood. In other words, the highlighted area below actually protruded farther out of the plane than the actual edge. If the bevel isn’t low enough, the highlighted area will hit the wood, and force the plane up as you are cutting.

After a bit of grinding I lowered the bevel a bit more, and the blade looked like this. I’ve found it to be a tricky balance finding the right angle. If the bevel isn’t low enough the back of the bevel will hit, but if you make it too low, the edge will be weak. Ultimately I’ve been aiming to take off just enough to keep the back of the bevel from hitting.

After grinding and making sure the back of the bevel was no longer hitting, I started to focus on the resulting angle of the test piece. I took a few more test cuts in some kumiko and measured what the resulting angle was. From there I could determine how I needed to refine the cutting edge in order to get a more accurate result. The blade pictured here is made for cutting 45 degree angles. To be clear, the blade actually cuts a 90 degree angle, but half of that (45) is what remains on the resulting kumiko piece.

After a test cut I checked the resulting angle. These two pieces should come together to form a 90 degree angle. Obviously the blade needs some adjustment.

Essentially the blade is cutting an angle less than 90, and needs to be widened. With ha-ganna to widen the angle you need to grind back the outer edges of the bevel. And the reverse is true if the angle needs to be narrower. Below I marked out where I need to remove material to readjust the cutting angle.

After grinding back the blade to the a bit more I took another test cut. This time I got closer but it was still not quite 90 degrees.

So one more round of reshaping the bevel. I ground the bevel back a touch more in the same way as above, and after resharpening did one more test cut. Finally getting a nice 90 degree angle between these two test pieces.

I went through all my blades (15, 30, 45, and 60) performing the same series of steps to adjust each bevel for an accurate cut.

With all the blades cutting I started using the ha-ganna on a kumiko project. One thing that I soon realized was that the blades that cut at a shallower angle (15, 30) are much easier to use. I think the main reason is that at 15, 30, and even 45 degrees the blade is cutting across the end grain at a steep slope. With these blades I was able to consistently and relatively easily sharpen and get clean cuts on my kumiko. In contrast the 60 degree blade, cuts much more directly across the end grain, making it a trickier blade to use. Below I modeled the 60 degree blade (top) and 30 degree blade (bottom) as if they were cutting across a piece of wood. You can see how the 60 degree blade has a tougher task of cutting across the end grain simply due to the fact that it cuts at a steeper angle.

The 60 degree blade has so far given me the most trouble. Actually, despite my best efforts I never got the 60 degree blade to cut really cleanly. I used a few different tricks to see if I could improve the cut but the results have been somewhat lacking. After doing a bit of research and witnessing how professional kumiko craftsman are able to get clean cuts on tricky soft woods like sugi, I decided to take another look at my 60 degree blade. There’s a lot to talk about there, so I’ll follow up with another post.

Thanks for reading,

Jon