Friday, January 30, 2015

Gateway (43)

Post 43 in an ongoing series describing the design and construction of a kabukimon, a type of Japanese gate. This is a project for the Museum of Fine Arts in Boston. Post 1 in this series can be found here if you'd like to start at the beginning. Each post links to the next at the bottom of the page. Recent installments also to be found in the 'Blog archive' index to the right of the page.

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Most of today was consumed with the last step on the wall posts, namely cutting the end tenons. The tenon arrangement is a double hammerhead, occupying about half the top of the stick. These involved several steps to cut out, and it took a good while to complete.

I was trying hard to hit my marks today. The spacing and thickness of the necks on the tenons was the critical bit. If the head is slightly skinny, or short, or the head angle a hair out, it is no big deal. The necks however are the starting point in cut out for indexing the tenon spacing, so I took care to hit my numbers as closely as I could.

Tenon neck spacing was set at 4.00", outside to outside:


The other post came out similarly:


Tenon neck thickness was 1.00" - here's one tenon neck in the caliper jaws, a hair over dimension:


And on the other stick, I hit the same number:


Another one:


And number 4:


The front surfaces of the tenons were decked a 1/4" and the cut out on the wall pasts was done:


Another view:


I used a go/no go gauge to check the hammerhead shoulder offsets:


I find that with careful paring with a sharp chisel, you can pare a surface to a +/- 0.003" without too much trouble - - so long as you can measure that accurately of course, and don't get too aggressive with the trimming. The tool needs to be reasonably sharp of course. The go/no go is 0.004" under target, which is of no consequence as I have yet to cut the mortises. I will want a slightly tighter dimension on the neck height on the tenon so that the joint draws down snugly when slid together.

All for today - next up on this project are the flanking posts, which I have already started in on. More tomorrow on that. On to post 44

5 comments:

  1. Very impressive Chris! I've noticed you use the digital caliper a lot for the precise joinery. For a novice hobbyist woodworker, is there an entry level brand you'd recommend?

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  2. Siavosh,

    I wouldn't bother with 'entry level' for any marking, measuring, or layout tools. Buy the best you can afford and experience the pain of purchase just the once, instead of the long distaste of a tool that cannot be relied upon for accuracy. I find Mitutoyo products excellent generally and would recommend their 'digimatic' line of calipers, along with their squares and rules. The calipers are extremely robust and long-lasting, not bothered in the least by fine dust, and I trust them.

    ~C

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  3. Given the tolerances you are meeting, and the grain direction being fit to, your go/no go gauge will be more stable with the longitudinal grain going the other direction.

    Also a very good podcast interview about Japan going "Medival" by James Howard Kunstler and Morris Berman.
    http://kunstler.com/podcast/kunstlercast-263-yakking-with-morris-berman/

    You are doing a wonderful job on this Gate Assembly.................Jack

    ReplyDelete
    Replies
    1. Jack,

      thanks for your comment, and that is true about the go/no go being more stable if the grain ran 90˚ opposite. However, I was using the gauge as a quick spot check on the 4 shoulders (it's not a tool designed for extended use), so in the course of a minute or three I doubt that significant dimensional change is occurring. It seems a non-issue. When I go to cut the corresponding mortises, I will check the dimensions again and make sure the mortises conform accordingly.

      ~C

      Delete
    2. Thinking about it further, I think the main reason I prepare the go/no go with the grain longitudinal is simply the fast that it is easier for me to achieve the required size accuracy by processing through my Makita shoebox planer than it would be to execute a crosscut to that level of precision. Of course, I could have crosscut over length and then used a plane to shoot it to dimension, but that would take more time. Definitely would like to improve my shop capacity in regards to precise cross-cutting at some point in the future.

      ~C

      Delete

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