Building a Himi Tenma in 1/10 Scale – Part 3

I’m making decent progress on the Himi Tenmasen model and am now working on the kanjiki planks. These are the bottom planks located either side of the heavy, central bottom plank, called the chyou. As I mentioned before, my model will have two kanjiki planks on each side, much like in the tenma drawings, though the boat built last fall actually only used one plank per side. But, this way allows me more efficient use of my wood supply, and if I screw up a plank, I lose less wood. And, while it means more mortises to cut, it also means there is more detail on the model.

Measurements of mortises given are at full size.

I’m working in Japanese measurements here, and the mortises I’m making are pretty common sized. They are trapezoidal. On the model, they are 2.5 bu long, and 1 bu across the wide end and 0.5 across the narrow end. 1 bu is approximately 1/8″, so this can be translated to about 5/16″ long, 1/8″ at the wide end, and 1/16″ at the narrow end.

To confuse matters more, I’m using Power Grip carving chisels to cut the ends of the mortises, and they are 1.5mm wide and 3mm wide, which are just the right sizes for the job. For the long edges, I ground down an X-Acto #18 chisel blade to size.

Using these tools, I cut all the mortises out of the kanjiki boards, then made plugs and glued them all into place. I made sure to let these dry thoroughly, because I’m going to be bending the boards to fit the hull, and that’s going to mean wetting the wood. I used Original Titebond glue for the mortise plugs, but probably should have used Titebond II, which is more water resistant. I’ll mention now that this didn’t end up being an issue, but I did use Titebond II to glue the boards together.

Next, I made sure I could bend the boards into position before I ended up cutting the boards to shape. Below, you can see how I used clamps and rubber bands to hold the boards into position.

You’ll notice the base board I’m using in the above photo. I finally broke down and made this new one that allows enough clearance underneath (1-1/8″) for the ends of the clamps to fit. I also wanted one that was relatively narrow, to allow me to reach the hull from either side, so this board is 5-3/4″ wide.

Fitting the boards to the hull involved a bit of spiling, and a Japanese boatbuilders technique called suri-awase, which is a method of fitting wood together by running a saw between the seams. If you want to learn more about this technique, check out Douglas Brooks’s book or website. On a model, this can be accomplished using a very thin Japanese razor saw. The one I have, I bought from It’s very thin, with a narrow kerf, very sharp, and has a little flex to it. But, I’m sorry to say that I don’t have any photos of the technique.

Using the pattern I cut earlier, I then shaped the outboard edges of the kanjiki boards, though I left a little excess. I do this now from experience. It’s always easy to sand away the small amount of excess afterwards.

Finally, using the arrangements of clamps and the internal mold I made, I was able to glue the kanjiki boards into place. I started by gluing the rear half of the boards to the central board, the chyou, and the bottom edges of the transom, the todate. After the glue dried thoroughly, I then glued the forward half into place.

The structure is now starting to look a bit like a boat.




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