Thursday, June 9, 2016

A Ming-Inspired Cabinet (60)

I'm sure many readers have drifted off to sleep by now with this series, but I'll forge ahead with new posts all the same.

Presently I'm working on the frames for the upper sliding doors. These frames are to be mitered at the corners, and will accommodate both a solid wood shedua panel and the recently completed latticework panels.

I decided to go with twin tenons on the frame corners. The reason for twin tenons instead of a single tenon relates to improved strength. How so? Given that the frames are 1.125" thick, a single tenon would typically be 1/3 of that dimension, or 0.375". If you consider that tenon as a volume, which is a way of gauging the number of fibers it places into the mortise, for this example the tenon volume is 0.264404 cubic inches.

With the twin tenon, each of the tenons has 0.17627 cubic inches, together a total of 0.35254 cubic inches, representing 33% more fiber than we see with a single tenon. Also, when considering a joint which will be glued, looking only at the tenons cheeks (the primary gluing surfaces), it is readily apparent that the twin tenoned version has twice the number of cheeks, so roughly twice the gluing area overall:


Finally, if the twin tenoned part represents the end of a beam, as it does in the case of these sliding door frames, the twin tenons provide greater support and stability against twisting than does a single tenon:


The caveat is that a single tenon represents a greater likelihood of a good joinery fit than do twin tenons, and thus the advantages of a twin tenon may be moot if the cut out results in a sloppy fit. Also, the twin tenon takes much longer to cut and fit, so it is hardly an economic choice. A single tenon is a fine, and adequate choice, but the twin tenon is a little better, putting labor cost to the side.

Here, following a roughing out of the tenons in respect to the thickness of the sticks, I am reducing the tenon height by sawing:


I chose to diminish the tenons so as to accommodate the dado in the frame. Were it possible to center the dado between the tenons and leave the tenons taller, that would have been most ideal, but the panel dado is off-centered in this case, and I wanted the exposed tenon ends to be evenly spaced on the faces which show.

We slice, we dice:


That excitement is followed by some chisel work:


These tenons measure 1/4" (6.35mm) thick, with a 1/4" space in between.

A completed twin tenon:


A while later, the tenons were completed on all of the frame rails:


The short pieces with mortises in the above picture are the frame stiles, which have had their mortises roughed out at this stage.

Another view of the tenoned rail ends:


You will undoubtedly notice that 4 of the sticks are tall and 4 are shorter. The tall ones will have a tongue cut into their upper edge to insert into the sliding door upper tracks, while the shorter ones will fit to the lower tracks and have a much smaller tongue.

While I've been working on the frames, I've been gradually gluing up the lattice work panels, getting one done per day. Today saw the last one into glue up. Once the glue has dried overnight, I plane the panels off to level everything out and get an even sheen.

The joinery work for these frame corners, meanwhile, does takes a while, partly due to the fact that the miters are slightly unequal, instead of being the more usual and easily dealt-with 45˚.

Here's one frame corner coming together:


The parts meet and the miter line looks reasonable for an initial fit:


The tenons will be wedged and glued sometime down the line.

Another view - this is the back face of the frame:


Here's another corner:


Another view, this being of the front faces:


The first frame took me most of the day to fit together, and here it is, with the lattice panel sitting atop just for a sense of what's coming:


Another view:


I'm intending to get through the remainder of the joinery in the next couple of shop sessions. Then I will rebate the frames, check the fits of the frames to the cabinet, and to one another, and finally mould the fronts with a bead.

All for this round. Hope you liked the progress report. Slide right over to post 61 if you like.

12 comments:

  1. Twin tenon vs single tenon......putting rotational strength, increased glue area,and additional work aside...the twin tenon just plain looks better...fits the "style" much better! Well done!

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    Replies
    1. Joe,

      appreciate the comment and glad you find the twin tenons pleasing to look at as well.

      ~C

      Delete
  2. Chris, thanks for detailing specifics about the additional strength of twin tenons. I've always liked them for increased glue area and rotational strength but the increased amount of wood fibers is interesting to see in number form.

    Nice work! I like the offset miters. I have my guesses on how the lattice work will be attached....spear point mortises?

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    Replies
    1. Brian,

      yes, the mortises/housings on the frames will mirror the points of the lattice. I had considered various solutions, but that is the one I am going with.

      ~C

      Delete
  3. Chris, this may become clear later but I was wondering why the miters don't meet in a point but rather show some end grain for one of the halves. Is it to accommodate the tongue you mentioned? Amazing and inspiring work as always...not sleeping here, thanks for keeping us posted!

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    Replies
    1. JL,

      the matter was alluded in the post - the long members of the frame will be rebated to leave a tongue, so for the moment you see the end grain exposure. After the rebating, only the tongue end will expose end grain, and those portions rest in the sliding tracks.

      Appreciate the question all the same and pleased to hear you like what you find here.

      ~C

      Delete
  4. Haven't fallen asleep yet Chris. I learn something on every post you do. I'm waiting for the final money pics.

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    Replies
    1. Ralph,

      thanks for the comment and I should forewarn you that those final pics are a ways off yet!

      ~C

      Delete
  5. I'm intrigued by your use of what looks to be a general metalwork vise with smooth jaws as a platform to guide end grain paring. I've seen steel blocks (1-2-3 blocks?) used for this in many of your earlier posts. Do you use the vise for that a lot? I like this idea, as my own experiments with formica-skinned plywood jigs have been tantalizing (they work!) as well as frustrating (they usually turn out to only work for very specific jobs).

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    Replies
    1. Jim,

      thanks for the question. It is a metal working vise, something i brought back from Japan with me when I left in 1999. I use it from time to time when I want to hold a stick in a certain position for paring work. Other times I clamp the stick to my planing beam with a Bessey K-Revo. Both methods work well for me.

      ~C

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  6. Chris,

    Never think for a moment that we're getting tired of these post. I look forward to checking daily to see if you've updated your page. Every post i feel i learn something whether intentional by you teaching/explaining a method or reason or just by watching your skill and patients in pictures. Keep up the great work, you inspire me to want to start cutting some of these types of joints.

    John G.

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    Replies
    1. John,

      thanks for that. This blog has bee an avenue to explore various topics, and sometimes I worry a bit that these long build threads might only appeal to a minority of readers.

      ~C

      Delete

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