Cutting Koshikake Kamatsugi (Stepped Goose Neck Splice)

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I thought after last week that somehow this joint would be easy. Its certainly straight forward in cutting, but there were some new challenges that made executing this joint much more than a walk in the park. Time from layout to a joint that actually fit properly, 4hrs.  Can you see that I added a taper to the back shoulder of the goose neck? I thought it would make things easier and pull the whole assembly tighter.

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Here, the layout for the female side of the joint. Both sides of the joint were marked out before beginning, no transferring of marks. All of the marking was done with a fine tipped marker (.3mm) and sashigane.

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The layout for the male side of the joint. I started my cutting with removing the bottom half of the lap.

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Once again, I did all of my cutting with the piece horizontal on the bench. For this joint I tried cutting horizontally, which I’ve never done before. Definitely felt a little strange, but I had already cut both sides of the line down to the shoulder with the saw vertically, so the saw was just finishing the cut. I should have stopped right here and sharpened the rip side of my ryoba, I knew it was feeling a little dull and floating around in the cut, but…but what, I don’t know. Sharpen your tools when they get dull and sawing is a pleasure of a challenge, not an exercise in frustration.

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With the waste removed and pared flat I finished the layout on the bottom. With the timber in the same orientation I cut down one side of the cheek of the goose head, flipped the timber over and finished the cuts all the way to the haunch shoulder line. Then I made the cross cuts into the neck.

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A chisel pared the waste along the neck line.

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As you can see, a bit more wood has to be mortised out to define the horizontal and vertical haunches. I also chamfered a lot of the outside corners on the bottom of the goose neck.  It  was right about at two hours in when I finished this side. I thought The other side would be faster, but mortising with a chisel always takes me longer than I think it will.

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For the female side, removing the step that houses the horizontal haunch of the male side, and finishing the layout.

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I used a saw to cut for the vertical haunch , as well as cut as deeply as possible into the goose neck before chopping the waste with a 3/4″ chisel.

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These interior surfaces are what make this joint so challenging. There are so many of them that need to be perfectly vertical, or the joint will never go all of the way together. I used a small bevel gage set to square to check. All of this paring and checking, it really slowed me down. I also used this bevel gauge as a depth gauge when paring the bottom of the mortise. It was nice being able to run my chisel, bevel down, to clean the waste from the bottom.

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I grabbed the taper angle from the side of the layout with my bevel gauge and marked the interior of the mortise wall. I thought about just eyeballing this for the cut using the markings on the side of the beam, but that would have been a mistake. Getting this taper correct was the key to having this joint fit properly.

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The finished joint. Well, I forgot one thing, chamfering the outside edge where the bottom of the goose neck meets the vertical haunch. That was mistake number one that kept the joint from going together all of the way.

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For the longest time the tip of the goose neck fit flush, but the step was still 1/16″ high. I took it apart, checked my surfaces for square and flat, pared a little here and there. I must have taken it apart a half dozen times and each time could not figure out what was preventing the step from sitting all the way down. Finally I realized that the taper at the back of the goose neck was too acute on the female side of the joint. It was keeping the back of the goose neck from seating all of the way, and I thought it was a problem at the step. I was wacking it with a heavy hammer, thinking, surely it can squeeze in there a bit more. Nope, it needs to be almost perfect. The joint fit properly after paring. The taper became snug the last 1/16″-1/32″ before the two joints were flush. With a good fit the two pieces of the splice lay in the same horizontal plane, flat on the bench. I did manage to introduce a little error in my marking, you can see a small gap where the shoulders meet over the step. I need to get faster! Way too slow, and I was trying to move with a purpose.

I’m ready for more, what do you think for next weeks joint?

6 thoughts on “Cutting Koshikake Kamatsugi (Stepped Goose Neck Splice)”

  1. I forgot about this week’s joint…Had to finish a project for my mom’s birthday, get working papers, and work.

    There’s some time before midnight strikes, though!

    1. wait wait wait, we still have 2 days don’t we? I could not get wood here in Valdivia, my friend was working and we didn’t have time to go buying. I’m back in Santiago tuesday morning, first time I do is that joint.

      1. Quite correct, the last day is June 30. But of course we would wait for you, this is about learning together. Jason sent me some photos of his joint that were really stellar. Fast too, I’m quite interested to read his write up and see how he managed.

  2. Awesome, I have an upcoming house build and I want to incorporate Japanese joinery in where I can. I have a lot of scarf joints to do, I love this one, can you tell me if it was used on the sill or up high on a beam? If on a sill, what joint was used on a beam or top plate?
    Thanks,
    Josh

    1. I would use kanawa tsugi, the rabbeted oblique scarf splice for sill, purlin, or ridge scarfs. I hope the house build goes well, definitely a worth while endeavour!

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