Ha-Ganna 葉鉋 : Making Dai

Ever since I started doing kumiko work I have wanted to try out ha-ganna　(葉鉋). Ha-ganna are specialty planes for cutting specific angles on kumiko pattern pieces. For larger projects with a lot of pattern pieces they really speed up the process by allowing you to mass produce parts vs cutting each part individually using a jig. Ha-ganna always seemed like mysterious tools. I would occasionally see a video or picture of someone using them but never had an opportunity to see them in person. At around $700 per plane they are also really expensive. So for a long time I thought they were too expensive. Then a couple months ago I was browsing through a tool dealers site and came across their listings for ha-ganna. The shop had an option to purchase ha-ganna blades separate from the wooden dai. The price was much cheaper so I jumped on it and bought the 4 blades they had available, and decided I would make my own dai.

Blade bedding angle

When the blades arrived I started to scratch my head wondering how to proceed with making the dai. Standard kanna have the blade set at an 8/10 slope (around 38.7 degrees). Having never seen a ha-ganna in person one of the first questions I had was what slope to set the blade in the dai. I searched the internet and found a couple of pictures that seemed to indicate that the standard 8/10 slope is used, but I didn’t turn up anything definitive. I’m still not positive what slope is typically used, so if anyone reading this has a ha-ganna I’d love to hear what slope you blade is set at. In the end I figured that an 8/10 would be the safest bet, and at that slope everything seemed to work out just fine.

Laying out the Dai

Once I decided on the bedding angle of the blade, I started laying out the dai. I purchased 22.5, 30, 45, and 60 degree blades, and each varies in width. For each plane, I measured the width of the blade and cut the dai so that there would be 8-10mm of material remaining on each side of the blade. From the outside edge of each side of the blade, I marked in 3-4mm for the area that will become the groove that wedges the blade tight.

Cutting the Dai

I used a combination of drills and chisels to rough out the majority of the cut.

Cutting into the side of the dai to establish where the blade rests against was tricky, especially for the narrower planes. The narrowest blade is only about 17mm wide, meaning the actual opening in the dai for that blade is only about 11-12 mm. So, I needed a really skinny saw to be able to cut the groove within that narrow opening. I didn’t have a saw small enough, so I ended up modifying a replaceable blade saw that I had lying around. It looks crude but did the job.

Below you can see the cuts made with the modified saw. You need to make these cuts as accurately as possible since they ultimately establish the final slope of the blade. They also need to be parallel for the blade to have good contact along both sides.

With the saw cuts finished I continued to remove the last bits of material before test fitting the blade.

Fitting the Blade

As soon as I was able to insert the blade into the dai, I began applying pencil and a bit of camelia oil to the the back of the blade. The pencil clearly shows the areas where the blade makes contact with the dai. Then it’s just a matter of shaving the areas that are touching, reinserting the blade, and rinse and repeat. I fit the blade until I got it close enough to the mouth of the dai to lightly tap it out with a hammer. This is the exact same process you go through when setting up a regular kanna.

Here’s a progress shot from fitting the 45 degree blade. You can clearly see the areas of contact between the dai and the blade left by the pencil and oil.

For trimming the areas of contact, I used a combination of small 3 and 6mm bench chisels. I also used these little sotomaru-nomi 外丸鑿 (outside-round chisels), which were really handy.

Below is the dai in progress for the narrowest ha-ganna. The blade for this ha-ganna was made at a 30 degree angle, for cutting 60 degree kumiko pieces. This dai was the trickiest to make since the blade was the smallest. However, with the modified saw blade for the side cuts and the small sotomaru-nomi for fitting the blade, things came together nicely.

Here is the finished set of ha-ganna, for cutting 22.5, 30, 45, and 60 degree kumiko pattern pieces. Overall the process was nearly the same as cutting a dai for a standard flat kanna blade, with a few added difficulties due the the angle of the blades and the narrow openings. But after cutting the first dai, the process became much clearer and the remaining dai were pretty straightforward.

Adjustable Fence

Next up I started fabricating the adjustable fences that attach to the side of each ha-ganna. For each fence I started by simply gluing up an L-shaped piece with some 15mm thick oak.

After the glue dried I clamped the fence to the dai, and drilled through the fence and into the dai for attaching a pair of threaded rods. I used epoxy to glue the threaded rods into the dai. Once the epoxy set, I threaded on a couple of standard nuts and wing nuts.

Ha-ganna that I’ve seen sold online always have a large diameter wheel-like nut on the inside of the fence, which I assume makes it really easy to adjust and fine-tune the fence. I searched all over for that kind of hardware but came up with nothing, so in the end I opted for a standard nut on the inside; not that sexy but it serves the purpose and ultimately isn’t that hard to adjust.

And here is the finished 60 degree ha-ganna.

That pretty much covers the dai making part of this ha-ganna setup journey. Next up I’ll cover how I went about sharpening and adjusting the blades, so stay tuned.

Thanks for reading.