Making Odate’s Japanese Transom Part 2: Mitered boxed mortise-and-tenon

Japanese transom frame pieces

With the main frame mortising completed the mitered boxed mortise and tenon can be cut. It is without a doubt the hardest joint I have ever had to execute, but fear not! It took me three practice tries to get comfortable with the sequence of layout. If you can follow along, this can be accomplished.

Mitered boxed mortise and tenon

Fundamental to being able to make a joint like this is the skill of sawing perfectly to your layout line and square. Desmond King, in his book “Shoji and Kumiko Design”, gives a great set of exercises for learning to run a Japanese saw straight and true in a cut.


It really, really pays to practice consistently to build up your muscle memory. I use a wooden cutting fence to start my saw kerf. I bring the fence up to my cutting knife that has been placed in the knife line and make a series of practice cuts on a squared piece of scrap pine.

Practice cuts

I do not mark a line on the side of the cut to tell me if it is square or not, you just have to be able to cut square. I make these practice cuts one at a time and check with a try square. Really pay attention to how it feels when you are cutting correctly. If you can do this fairly consistently you’ll save a lot of time paring your joints with a chisel.

Cutting tenon cheeks

Although I originally learned to rip the tenon cheeks before cutting the shoulders, Odate does the opposite. The rationale is that you can over cut your shoulder without it showing in the finished joint, but if you over cut the cheek it will show. Cutting the shoulder first gives you more feedback when you reach the bottom of the cut on the cheek. This is the time to be fearless and cut right to the line. I find that if I’m afraid of overcutting the line my hand will twist the saw away.

Veritas plow plane

Of course, I’m no master tategu-shokunin and most of my saw cuts require a little cleaning up. I use my Veritas router plane with an auxiliary fence to trim the tenon cheeks to the line. If you don’t have a router plane check out Paul Sellers video on Youtube “The poor man’s router”. Sellers is old school and awesome, I’ve learned a lot from his videos and hope to get his books some day.

Shooting board

With all of the mortice boxes cut I trim the end of the joint square on a shooting board. I left an extra 1/8″ on the end of each joint for this purpose.

Marking mortise box height

Now the end of the joint is a consistent reference for marking the top of the mortise box. Leaving any less wood than 1/4″ would create a problem when cleaning the mortise for the box on the tenon.

Cutting mortise box

Here’s the cut, once again started with a little wooden fence and cut straight down. To complete the cut you flip the piece over and make a starting kerf on the outside miter line.


This cut gives the teeth of your rip saw an nice place to start when cutting the miter.

Miter cut

Just like cutting the secondary shoulders on any fully housed tenon you cut away from your shoulders to avoid scratching them with the saw.

Paring endgrain

Trim the joint up, paring the end grain on the diagonal from both directions to avoid gouging your shoulders with the chisel. If you’ve managed to make it this far you are rewarded with half of an awesome looking bit of joinery.

Finished boxed mortise

This post is getting quite long, so I’m going to break this up into another post. Look for Odate’s Japanese Transom Part 3: Mitered tenon and final transom assembly.

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