Wednesday, July 13, 2011

Coffee Anyone? (15)

Station 15 on the climb. If you're new here or haven't visited in a while, I'm in the late stages of a project to make a glass-topped coffee table with a joined bubinga frame and shelf. Previous posts in this thread, along with postings and threads on a variety of other topics can be found in the "Blog Archive" on the right side of the main page.

Last post ended with a cliffhanger of sorts, well, a different sort of hanger really, as I was mid-way through fitting a draw bar. The draw bar connects the main table top frame members together at their re-entrant corners:


The center of the bar is cut away with opposed rebates, a bridle joint if you like, to fit onto the twin tenons atop the leg. The gaps on the ends of the draw bar in the mortises are there deliberately, allowing room for some elastic compression as the joint gets mechanically drawn tight with the wedge pins, shachi-sen.

The tenons had been largely defined through the CNC stage of the work, however I needed to do some additional trimming:


And the same process with the front side:


Now I could try the fit, though some trimming is still to be done on those tenons in another location:


The last couple of millimeters required a little hammer and block assist:


Down:


Then I fitted the assembly of draw bar and leg to one of the frame members:


Then I fit the other side frame member to the assembly, independently, and finally was able to slide the whole shebang together:



The joint drew up decently:


A view from the front:


And a view looking up slightly from the front:


 Next, a view of the inside corner of the frame with the leg attached:


And for good measure, a side angle view of the connection:


 The joint isn't complete yet, mind you. I need to deal with the shachi-sen, which will lock the joint together tight. First task was the layout and knifing:


The other side:


Then I disassemble the works and complete the layout on the frames and the draw bar:


Time for an episode of Sawing for Teens:


And then some paring:


 The completed draw bar:


Then on to the trench cutting on the inside walls of the frame member end mortises, first sides:


 Then abutments:


The completed mortise:


Next post in this thread will have some pictures of the completed joint going together. Hope to see you then.  --> on to post 16

6 comments:

  1. Isn't that a very interesting technical joint!
    The slope of the grain at the shachi-sen scares me though :-)

    ReplyDelete
  2. Gordon,

    Yes, it's definitely better on one side than the other. Remember though that the sides of the twin tenon bear against the wood in the mortise, so the portion that the shachi-sen pushes against has nowhere to go. I'll be judicious in how firmly down I drive various shachi.

    Thanks for your comment!

    ~Chris

    ReplyDelete
  3. Hi Chris,

    I was wondering how Sashi-Sen stay in place for a while, but this desing really made me want to ask. Since there is nothing under them once the table is upright, what holds them in place? Is it friction only, or is there more to it?

    Thank you.

    Eugene

    ReplyDelete
  4. Eugene,

    thanks for asking! The shachi-sen are held in place with the friction that results from their compression in the joint. And since they bear primarily against end grain, both within the mortise and upon the draw bar, wood movement has very little effect upon their fit.

    ~Chris

    ReplyDelete
  5. Chris, any chance you could detail the cut-out process for the shachi-sen, as the they seem to be paralleloram shaped, small and, I imagine, quite fiddly to make?

    Looking great!

    richard

    ReplyDelete
  6. Richard,

    I thank you for your comment. I carefully and exhaustively detail the geometry and cut out for shachi-sen in The Art of Japanese Carpentry Drawing Volume III essay, so i won't be going in to that here on the blog.

    ~Chris

    ReplyDelete

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