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Joints For No Reason - Osaka Jo Otomon Hikae Bashira Tsugite

author-gravatar joelav Mar 27, 2017

I like to practice traditional Japanese joinery in my spare time. While these joints are architectural in nature and don't have much of a role in furniture making, they are great at building skill. This is the osaka jo otomon hikae bashira tsugite. 

I started with a 2.5" square hard maple turning blank that was a little spalted. I should have used a different piece because it was soft in a few areas, but it worked out okay overall. I planed it flat and square

Now to cut it in half. I start by making a knife line all the way across all 4 faces    

Then I saw across the top and down one face at the same time, but not going all the way through yet 

When I flip the piece around I have kerfs to follow which help keeps everything square

Laid out the joint. This joint has 2 dovetailed faces and 2 birdsmouth (mitered) faces. The layout was very tricky to get right as I couldn't find anything other than illustrations to work from. The V's point to the side of the line I need to cut to. I prefer doing this to coloring the waste in or drawing lines. It avoids any confusion (in a very confusing joint)

I started with the tails. This is a compound dovetail - it's tapered on both faces. Also it does not go through the piece as it stops in the middle. Accurate sawing here is critical because both faces are angled and that makes paring difficult. I used a fairly coarse dozuki as my finer ones wanted to drift in the thick stock

For the birds mouth, I chiseled to the lines pretty deep. This aids in cutting, and it gives me a good registration for my chisel to pare the waste after cutting. Paring should be done very sparingly as any material removed form the face makes the birds mouth shorter and will not seat properly

I carefully sawed the waste being mindful of where my tails ended and began as not to saw into them

I then cleaned up the joint with a chisel

The pins side is a bit easier to saw. On one face I can saw straight through because the saw exits into the waste of the opposing pin. If I had laid the joint out more carefully, I could have made my life a lot easier and made sure both pins could be sawn straight through. Next time.  

Now for the birdsmouth. This was challenging. Starting the saw on the edge of the piece and then sawing down on an angle. Like with the tail piece, I chiseled into the waste a bit

Now i removed the waste from the tails. These are angled on both faces so careful chiseling is needed

This is how the joint goes together. Here is an animated illustration as well. 

The dovetail side. Not bad. I oversawed the tails a bit and the fragile mitered edge broke out a bit during assembly leaving a small gap. But it's really tight and square. In fact I can't get it apart again

The birdsmouth side - complete with worm holes and an arrant chisel blow. 


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