Wednesday, June 17, 2015

Japanese end joint (Okkake daisen tsugi)

For the porch I am going to need some planks that are longer than what I have on hand.
I could go the easy route and just bolt, screw or nail some together, but this is part of what I really like to be doing, so I didn't want to cheat myself from trying out a nice carpentry joint.

The Okkake daisen tsugi is also sometimes called Wari tsugi. In English it would be called a "Dadoed and rabbetted scarf joint".

My main source of inspiration for these joints is the book: The complete Japanese joinery, published by Hartley and Marks.

That book is an absolute treasure trove of information on the subject. There is even a description of the religious ceremony to be held prior to building a new home.
I can highly recommend the book to anyone interested in the subject of Japanese timber framing joinery.

Using hand tools only, it takes me roughly one hour and fifteen minutes to complete both joints on a set of 3x6" planks to be joined.
I need to complete a total of six long planks, so I might even get a bit faster when it comes to the last joint.

Today it is raining, and all the concrete pillars have been poured, so it is a welcome change to do some work in my workshop.

The female part of an Okkake daisen tsugi.

The set up, sawhorse and shop stool.

Halving the dado.

The completed joint. 

This is about the maximum length that is workable inside the shop. (6.5 m)

The tools used to make the joint.


  1. both edges of the joined boards still have saw marks on it. Where did you reference all the layout lines from?

    1. Hi Ralph.
      I just tried to do the layout from the "same" side of each board. In the end a little bit of fine tuning was needed, but actually not that much.

      If one board is a bit more or less than 3" wide and 6"high, then it won't matter much because measuring from the same side will assure that the joint will be tight and sound. Maybe there will be a height difference on the bottom of the assembled plank, but that's OK. I need the top side to be flat and level. The lower side will get bolted on to the brackets that are mounted in the concrete.

      If the boards had been 100% identical as in surfaced on all sides, I guess it would have been easier. But these boards will end up being hidden, and they are accurate enough as it is.
      Most of the Japanese joints I have looked at in the book have some sort of reference point in the centre of the board. But this particular joint will not work that way if the two boards are of a different width. So I just choose one primary side and go out from that one and the top of the plank.


  2. I have seen pictures of scarf joint before, but now I ask myself how must it be oriented?

    With your 3"X6", I guess the 6" side will be vertical. Is it the recommanded orientation for this joint?
    Just asking,
    because if you Google "scarf joint timber" or "trait de Jupiter charpente" the pictures show it with the other orientation.
    Or maybe I do not interpret correctly your or the other's pictures.

    1. Hello Sylvain

      Thanks for your comment, it is an interesting subject.

      I am orienting the joint so the 6" part is vertical. It will be used as a joist for the porch.
      I just took the pictures with the joint "flat", because that was how I figured I was able to get the best photo of it.
      Photography is definitely not my strongest side.

      As far as the orientation, it is what they show in the book, so I guess it is how it is traditionally oriented in Japan.
      But as you mention it, I think that the orientation is traditionally the other way in Denmark i.e. horizontal.
      In Denmark something similar like this is commonly called a "French lock", and most carpenters are amazed if you tell them that you have made one.
      Logically I would think that the beam is strongest if the joint is made vertical, if it has to take load from the top.

      A couple of years ago I made some Kanawa tsugi joints in the stable. The book translate that as a half blind tenoned, dadoed and rabbeted scarf joint. Looking at the drawings again, I can see that I oriented that joint wrongly according to Japanese tradition, but correctly according to Danish tradition.
      That was made in 6x6" timber and I had to join 4 beams to one long beam. It doesn't hold any load, but it is very prominently displayed. It basically holds the upper parts of the posts that form the individual boxes inthe stable.


  3. I see some familiar tools on your bench! Some of them used to be on mine!

    It looks like you broke down and got yourself a new German slick. Or, did you rehab it?

    1. Hi Brian.

      The slick was a gift from my father for Christmas. The only rehabbing I did was to paint the handle end of it.
      I saw that was how Olav had done it, and I liked the idea.
      All his tools are the same maroon colour, so I opted for a Volvo tractor red instead.
      The saws are from the tool chest that I also got for Christmas. One of them is field for a rip cut, and there is a lot of rip sawing on these joints.
      The mortise chisels work really well. The mid sized one is just the right size for this job.
      I only used the shoulder plane on the first joint, but that was so tight to begin with, that I couldn't get it seated properly before dressing the diagonal shoulder a bit.

  4. document from Timber frames guild:

    1. Hi Sylvain.

      That is a nice paper on timber framing. I can see they orient the joint horizontally.
      In the paper on page 11 there is a joint they call bladed and cogged. That one is similar to the ones I made in the barn except for the dimensions. I think my ends were about 1/6th of the total height/width of the beam.


  5. Replies
    1. Thanks.
      It feels nice to be able to do some fun woodworking in a project like this.
      The weather is typical for a Danish summer - it is raining and there is a lot of wind, so being in the shop is a welcome change.