Cutting Okkake Daisen Tsugi (Rabbeted Oblique Scarf Splice)

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Peter, who stopped by last weekend, was kind enough to let me photograph a set of old Japanese chisels he had picked up on etsy. This set is quite characteristic of some of the great deals to be had. I forgot to ask what the cost was, but it was probably close to the cost if you bought new only the 48mm chisel on the left.

I really love to see the worn down chisels. You look at that and think, don’t you want to have a bit more registration surface on the back of your chisel when paring? I suppose by the time you ware that much steel off in sharpening, you don’t need the large flat, you can just pare flat.

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I made the layout for this joint to show my guest Peter, it not being strictly part of project mayhem. It sat there looking at me in such a compelling fashion that I had to go ahead and give it a try. My first oblique splice, among the many variations of this joint that exist!

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Because both halves of the joint are very similar they are divided into the upper wood and the lower wood. I’m finally starting to realize how the sashigane speeds up layout. I’ve been using 1/2″ as a sort of nominal gauge for a lot of the haunching and, in this case, rabbeting marks. The sashigane being 15mm wide, it is used for the same purpose, but directly, so no measurement is required, you simple use the tongue of the square as the reference.  I recently ordered “The Complete Japanese Joinery” and am hopeful that it can give more insight into these time and accuracy saving uses of the sashigane.

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Before I begin describing the cut sequence, a note. Cutting a joint like this where the two haves are almost the same is great practice! What I quite obviously did wrong for the first half was corrected, and the second half actually gave me the chance to apply my new found knowledge.

I started the first half with the rip into the main cheeks of the scarf. I started the cut with the saw vertical, and then rotated the timber so that I could saw along in horizontal fashion. Its definitely a new skill to turn the saw on its side. I seem to let the top of the plate rest on the bottom of the kerf, producing a cut that slants upward away from the line. Its difficult without more experience to get a feel for the saw in the cut. If you stand up too much you’re bending the saw and things go awry, kind of like swinging a golf club.

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I stopped the rip cut when I realized I hadn’t thought through where I was going, and cut the shoulder line so that the rip had somewhere to meet up with.

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Paring such a large flat surface was difficult! Too much time spent carefully checking with a straight edge, and very easy to gouge in and remove too much material. The surface quality of my cheek suffered as a result.

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I marked the taper that draws the two halves of the joint together in assembly and made a series of waste cuts to the line for the lower cheek, which were then chopped with a chisel.

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Don’t you just hate it when you’re paring across the grain on a cheek and blow off part of the line? The line is all you have.

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In any case, the cheeks were pared flush and the layout finished for the through pegs that lock the joint. Evidently the square peg gives you the option of using a double wedge to lock the joint and tighten incrementally.

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The housing for the rabbeted tongue on the tip of the scarf was chopped last, after sawing to the line on both sides.

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For the second half of the joint I wised up, starting the cut with the rabbeted nose so that I had full support while paring the surfaces. For the cheeks I started with the shoulder cut and repeated my horizontal rip to the shoulder, and then immediately made the series of waste cross-cuts that allow the waste to be chiseled out for the lower cheek. Now there is room to plane the top cheek surface with a kanna, incomparably easier than paring. At the size of these joints you’re basically paring the face of a small board, the kanna makes sense.

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I took the fence off of my skewed rabbet plane to pare the lower cheek. I’ve never used this plane to pare such a large surface, it was awesome and fast.

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The first fitting of the joint was really disappointing. I know from previous experience that I could pound on this joint all day long with a sledge hammer and it would never come together. Bring the hammer out for the last 1/16″ or so of fit and not before, its better than waiting for rainbow farting unicorns to descend and push the joint together.

I spent a bit of time looking at the joint, trying to figure out what surface was proud. It must have been a small error in measurement, my sashigane technique. That is, marking one side of the scarf slightly longer than the other. I had to pare down the rabbeted nose on the left in the photo, as well as the shoulder that forms it, by almost 1/16″ before the two halves met nicely. I just don’t imagine having the luxury of repeatedly trial fitting a joint like this if the scarf was connecting two large, long, and heavy ass beams.

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I already had some cherry scrap planed to 1/2″ square, so that’s what was used for the draw pin. Because of how the joint slides together, I would think that trying to use the draw pins to force in the last little bit of fit could lead to splitting along the cheeks of the mortise walls.

The first meetup for the new local Japanese carpentry group will be next weekend. I’ve been surprised at the level of interest in such a short period of time, it will be an awesome experience to work together for the first time, figure out what can be accomplished when we learn together, even if just to drink a beer and joke about our mistakes. I had in mind that this joint, or a variation thereof, would be the work of the day and I encourage anyone to step up to the challenge. If you don’t have a little bit of an ‘oh shit’ moment when you first look at the joint, then you probably need to practice something more complicated.

2 thoughts on “Cutting Okkake Daisen Tsugi (Rabbeted Oblique Scarf Splice)”

  1. I think that you will like the Nakahara half of the “Japanese Joinery” book. I am reading it now and it seems to be the best of what I’ve seen so far. I am going to be studying it for years, I expect.

    1. Thanks for the heads up about the book, that is what I am hoping. When I first started with the Japanese joinery it was cutting the joints that compelled me. Now I can see that it is design, layout that is the real skill. Knowing where to put the line.

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