Kama-tsugi / Gooseneck Joint

Continuing on with joinery models this week…

Aside from making the 50 kanawa-tsugi joinery models (see the previous posts 1, 2), I was also tasked with making a set of 4 slightly larger joints which will become available for guests and visitors of the Japanese garden to play with. The idea is to show a few of the joints used in Japanese carpentry, and give visitors the ability hold, assemble and disassemble the joints to see how they go together.

First up was the kama-tsugi (鎌継ぎ) or gooseneck joint. After laying out both halves of the joint, I started cutting out the male end, beginning with some rough cuts at the table saw to establish the straight portion of the gooseneck.

To fine tune the dimension of the neck I used my router to trim the waste down to the finished dimension.

Below you can see the finished cut after routing. Here you can also see the sloping shoulder cut which I made with a handsaw.

A nice square cutoff made for a decent paring block to guide my chisel for cleaning up the sloping shoulder.

The inner end of the joint has a pair of stub tenons, and require set of matching recesses to recieve them. Here I’m getting ready to drill out the waste for those recesses. You can just barely make it out, but I hand sawed the shoulder cuts for the recesses before drilling, which helps to prevent grain from tearing beyond the shoulder line when drilling.

And here you can see how one recess looks after some chisel work to square up the corner and pare down to the layout lines.

With the recesses done I could move forward with cutting out the rest of the gooseneck part of the joint. The height of the gooseneck is only half the thickness of the overall material height, and below you can see how I started to remove material to establish the finished height of the gooseneck. I left two standing chunks of material to act as support for my router, so that I could safely trim down to exactly half of the overall stock height.

After establishing the finished depth with the router it was just a matter of knocking out the support chunks…

…. followed by a bit of chisel work to level everything out.

And finally I rought cut out the shape of the gooseneck.

Then it was time to move on to the recieving end of the joint. Here I’m drilling out the waste in the area that will receive the long gooseneck.

While there was still plenty of supporting material remaining, I also made a pair of cuts with a hand saw, and hogged out a stub tenon recess on the end of the joint using the router again.

Then I used a combination of the router and chisels to finish cleaning up the straight portion of the gooseneck slot.

Here you can see the joint after cutting away a bit of material from the upper half of the end of the joint. The protruding stub tenons on the bottom half will engage with the recesses that I previously cut in the other half of the joint.

At that point all that remained was to finish cutting out the gooseneck recess. This part of the process is all chisel work, and it takes care to do the cutout as cleanly as possible.

At last, here are the two halves after cutout was complete.

The goal for this joint (and the others as well) was for the fit to be loose enough that it could be easily assembled and disassembled, while also keeping the seams as clean and gap free as possible. That’s a lot easier said than done.

Initially the fit between the two halves was really tight, so I needed to carefully remove materail until the parts just came together, being careful not to remove too much material, resulting in a sloppy fit. I decided to try coating one half of the joint in sumi ink to help reveal areas of contact when fitting the two halves. The idea was that as I put the two halves together the sumi would transfer to the clean half of the joint in the areas that were contacting and rubbing. Then I could just trim those areas until the joint was fully seated.

The gooseneck recess was particulalry tricky to fit. There are a lot of areas of contact, and it’s easy to misjudge where the joint is binding up and remove material from the wrong spot.

For the most part using sumi to reveal the contact points was helpful, but it’s not a foolproof method. For example as you fit the joint it will get to the point where you can easily slide it together partway before it starts binding up. The danger is that sumi will still transfer at “light” contact points even when it’s easily sliding together, tricking you into thinking that material needs to be removed when it doesn’t. So it takes a lot of care and attention to determine exactly where material needs to be removed.

Here’s the finished joint after hand planing, and finishing.

3 more joinery models to go, so stay tuned!