Wednesday, January 20, 2010

Battari Shōgi 16

This is the 16th post in the series, with previous episodes archived to the right of the page. If you're arriving here from a link elsewhere, please be aware that this is not the current page on my blog.

The presentation at the Boston Children's Museum this past Sunday, for the Japanese New Year's festivities went fairly well. Many many children were really captivated by the small joinery examples that I had for them to take apart and re-connect. Some of the adults were interested too, and I gave away lots of business cards - I ran out of them in fact. During the 5-hour demo, I assembled my irregular-splay sawhorse, then the shrine lantern and then proceeded to cut a timber joint. I'd like to thank my wife for all her help during the event, along with the museum staff who provided assistance at innumerable instances. Here's a couple of photos from last Sunday that I would like to share....

Working on the cogged lap joint for the nuki:


The joinery between the two 'beam' sections being checked for fit, with the 'post' section on the ground at left:


In this one the joint is together and rotated 90˚to sit on my sawhorse:


A close up:


The joint is called shachi-sen sao-tsugi, and is about 2mm or so from being drawn up tight in the above photo. I didn't have enough time during the demonstration to cut the wedging pins, so I left it at that. In that type of joint it is important to leave room at the end of the rod tenon (about 3mm or so) so that the wedging pins can be driven in further at some later point, if need be, to accommodate shrinkage in the post. That's one of the details they don't tell you in some of the books, and it is, for that matter, a joint often mis-illustrated (as it is in The Complete Japanese Joinery for example).

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On the shōgi project, the long-anticipated moment of final glue-up has begun. Today I cut some 40 wedges. I decided, after much humming and hawing to use Wenge for the wedges. Often one might choose a wedge from a contrasting wood, but I wish to de-emphasize the joinery in this case, since the through tenons on the piece are already enough pizazz, and the original was less elaborate anyhow. If I make the bench into too much of a 'showpiece' (lacking a better name to give it at the moment) then I risk making the piece too out of character with the rest of the building. also, Wenge is pretty darn hard and crush-resistant as it is, so finding a harder wood with which to make wedges was already problematic. I considered using Lignum Vitae for the wedges, but I don't think it could be glued effectively with anything other than epoxy, and I wanted the joinery to employ a reversible glue. I considered Gabon Ebony as well, but couldn't see any significant advantage to that wood. So Wenge wedges it is - definitely hard enough to od the job ,and should be very discrete in appearance. I should add that I'm using liquid hide glue in this case, which I hope will bond the Wenge adequately - in any case the wedges everywhere will structurally lock the piece together so the glue is really back-up. To take the piece apart later, if necessary, given the use of wedges, the only possibility will be to drill the wedges out, which would then require some patching work. Not totally ideal I guess. But at least the parts will be separable if it becomes necessary down the line.

After making the wedges, I got busy cutting the wedge kerfs in the cross-piece tenons using my handsaw, first one side:


And then the other:


After the cross-pieces were kerfed, I did the twin tenons on each end of the two short side rails from the frame:


Then it was time to tape up all the areas around the joints to minimize the glue clean-up afterwards:


For step one of the glue up, I assembled the swing-down leg assembly, then slugged a couple of wedges in:


Then followed that by a check at each end with my SuperSquare to make sure everything was nice and square between the stretcher and each leg:


Tomorrow I will trim the protruding tenons and their wedges on the leg assembly, and then can proceed with the main frame glue up. One of the nice things about working with hide glue is its comparatively long open time compared to most adhesives, which allows for relatively non-frenetic glue up to take place. That's my hope at least!

I should have it assembled tomorrow. Stay tuned! On to post 17

5 comments:

  1. Hey Chris, isn't this supposed to be #16 in this series? (maybe you're just seeing if we are paying attention).

    Steve

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  2. Thanks Steve - duly corrected! I'm glad to see that someone was paying attention, as I obviously wasn't!

    ~Chris

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  3. Fantastic post Chris. I'm happy to read that the presentation captured the attention of so many. Thanks for including the photos.

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  4. Chris,
    On the shachi-sen sao-tsugi, how much angle are you putting on the wedges. I'm guessing between 4-10 degrees, since too little doesnt create much wedging action and with too much would tend to pop out.
    I'm doing this joint to attach legs to the "uprights" of some horses I'm building. (something I saw at Daiku Dojo).
    I'm pleased with their shape, but they have technical issues I discovered after the build. Its helpful to know that you have to critically read some of the joinery books out there.

    Side note: under the RSS subscription section here the RSS Comments window only shows "1 1/2" options. its like the window is too small or wont let you scroll down to view all options

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  5. Heffesan,

    both the pin (the shachi-sen) and the 'mortise' for it are tapered, and 1/10, about 5.7˚ is typical for the taper. Beware though of the side effects of the tapered opening and wedge combo.

    Whether the pin and mortise for it form a tapered rectangle or a tapered parallelogram (those are the two main styles of doing it, and there is a third method which I have come with), when you make that taper there are some issues of internal interference that come up. These are not obvious! If you develop the joint in 3D you can readily explore this matter. I'll be detailing such issues when I write the first volume in my series on Japanese joints, (which may by volume III or IV, I'm not sure yet). Thanks for the question. I'm not sure what, if anything, I can do about the RSS dealie-o, but I'll take a look to see what I can find.

    ~Chris

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