Kai-no-kuchi Splicing Joint

Hey folks. It’s been a busy few weeks with lots of time being devoted to prep for an upcoming craft fair, among other life things, but I still have some pictures to share from the joinery models I made a while back, and next up is the kai-no-kuchi splicing joint (貝の口継ぎ).

I really like this splicing joint. Compared to others which can get pretty complex, the individual parts of this joint are pretty simple, and both halves are identical. That said the contact areas on this joint are really broad, which makes getting a clean fit with tight seams a challenge.

After milling the stock and cutting the two halves to length the first order of business was layout. Here’s the stub tenon layout on the end of both halves.

From there I roughed out the stub tenons using a trimmer.

Then moved on to cleaning things up with a chisel, which was all the work required on this end of the joint. Pretty straightforward.

The next phase involved cutting away a massive amount of material from the faces adjacent to the stub tenons. Here I’m roughing out the cut using a hand saw.

Then I used a forstner style drill to hog out most of the waste material.

Followed by some chisel work to clean up things up.

When all is said and done you end up with parts that look like this.

The next bit of work requires cutting a set of grooves on the inner end grain portions of the areas I just cut out. Those grooves will receive the stub tenons cut at the very beginning. Before laying out the grooves I cleaned up the end grain using a chisel and paring block.

After cleaning up the end grain I couldn’t resist doing a quick test fit to see how the two halves were going to fit. If all the layout and cutout goes well the joint should slide together with the stub tenons bottoming out on the end grain portions of the joint from the previous photo.

But that’s when I noticed some trouble in the form of a crack developing in one half of the joint. I think the cherry I was using here either wasn’t fully dry/acclimated to my shop, or it had some serious tension in the grain… or perhaps a combination of the two.

Once I noticed this crack I started looking around at some of the other joints I had cut from this material and started to notice other cracks developing, which was a bummer. After mulling it over a bit I decided to abandon this joinery model and start over from scratch using some different cherry that had been sitting around in my shop for a long time… and therefore hopefully more dry and stable.

So here we go for round 2.

I fully intended to show the cutout process on joint #2, including the cutout of the grooves to receive the stub tenons but accidentally deleted the photos from my camera before loading them onto my computer… another fail from this project. So my apologies for the lack of detail shots showing the full process.

In any case here’s one half of joint #2 after all the cutout was complete. You can see the sumi ink transfer marks from the other half which show where the two halves are rubbing. Like the other joints from this series, I needed to make the fit between the two halves loose enough that a person handling the joint could easily disassemble it. So once again the challenge was to remove just enough material to allow the joint to be somewhat loose, while trying to keep the seams as gap free as possible.

I used a chisel to very carefully and slowly remove material from the areas marked by the sumi ink.

Here’s a look at the two halves of the joint going together.

You can see by this point the main contact areas were just on the outer edges along the inside faces of the joint. I was most hesitant about removing material along the edges for fear that the seams would become gappy.

Here you can see the joint further along in assembly and the interaction between the stub tenons and mating grooves.

And here it is all together. All finish planed and coated with a coat of liquid glass finish.

Here’s another version of this joint that I previously made just for the fun of it where the stub tenons are blind. I really like the look of this version, it’s much cleaner looking when the two halves of the joint are assembled. Cutting the stub tenons for this style is no big deal, but cutting the mating blind mortise/grooves is much harder.

That’s it for this round of joinery models. I’ve got one more after this to share and that should wrap things up for now.

Thanks for reading.