Sunday, December 20, 2009

Battari Shōgi 2

In the previous post, I described in detail the meaning of battari-shōgi - a folding bench installed on the front of Kyōto-area merchants houses, and showed some examples of these benches. Today I'll share with the readers the bench at the Bostons' Children's Museum as I found it, and begin the process of constructing a replacement.

The bench is made from Southern Yellow Pine, I do believe, and was constructed at the same time as the machi-ya installation into the museum. Thirty years of wear has left the frame of the bench quite eroded, and the panels with a delightful texture:


Nearest to view, the short-side frame member also has a long crack on it, though that did not become apparent until I had the piece back at home and commenced work upon it to remove the panels. I will keep the panels and construct a new frame. The existing frame joinery is a butt-jointed affair with screwed and plugged connections at the corners. The panels are held in a groove in the frame and are affixed to the cross-pieces with domed brass finishing nails. The panels attach to each other along their edges with double-pointed nails.

Here's a look at the bench folded up:


The cross pieces on the bench are tenoned and glued to the long frame rails. I plan to replace them with wedged through-tenoned parts, probably without glue (or I'll use rice-paste glue).

The hinges for the fold-out legs are formed out of 2"x2" stock - here's the right side one:


The other end:


The 2"x2" hinge pins are screwed to a cross piece at one end, and mortised into the frame at the other. Later on, I had the pieces apart:


The cylindrical part of the pins is not lathe-turned but formed using - presumably - chisel and plane. They are not perfect cylinders by any stretch, and therefore the fit to the corresponding holes in the legs is somewhat loose. I don't plan to duplicate that aspect of the previous fabrication.

Here's a look at the other end of the bench, folded up, showing, for one thing, the lovely metal catch that serves to keep it in place (one at each end):


At the bottom of the picture can be seen one of the two support brackets. The long side of the frame at the rear terminates in a pin, about 1.5" diameter, which fits into a socket in each bracket. Like the singing leg hinges, these main hinges were not made with precision, and likely had a somewhat sloppy fit from the get-go. Thirty years of being raised and lowered had caused the pin and socket interface to become quite worn, as one would expect and so loose that I was worried the bench could slip right out of the hinge. The looseness of the hinge points had led in turn to a lot of wear on the bottom edge of the bench frame - about 1/8" of wood had eroded away from the edge, also visible in the above picture (and the third picture above).

Here's a picture of the pair of support brackets, showing the condition of the sockets:


The brackets were fastened to the building by carriage screws and metal screws. The connections were very firm and took a little careful investigating to discover. I'm planning to use timber screws to fasten the replacements into position.

And as for the replacement, well, which wood to use. The museum agreed that replacement of the SYP with the same, or another soft wood, was not worth the trouble and expense. I suggested that, given the extraordinary wear and tear on the piece, compared to a 'normal' situation, it would make sense to construct the replacement frame out of a much tougher wood. There were a few possible choices in that regard, and it was recognized that the ideal choice would be a wood which matched the dark stained color somewhat closely, as a stained piece would suffer the issue of needing somewhat regular renewal of the finish, re-surfacing and so forth.

After some thought, I concluded that Wenge (millettia laurentii) would be an ideal choice. Wenge, a member of the legume family of plants, is found primarily in the open forests in the Southern Regions of Tanzania and Mozambique, and also occurs in periodically-inundated swampy forests in that region as well. It is a tree of medium size, growing 50~60 feet in height with a trunk diameter in the 30~36" range. It is a highly bend- and shock-resistant wood, that seasons without much distortion. As with many woods, the harvest of this tree is apparently not sustainable at present and it is only intermittently available from suppliers. A lot of the available timber is processed into veneer and flooring, and the bark is harvested in it's local area for the reddish sap, termed kino, an astringent and medicinal. It's fairly expensive to buy. I have not had much experience working the wood, though I know it is a bit challenging to polish. I happened to have one plank already on hand in my small reserve pile - it had found use previously as a planing beam. I ended up buying another 4 foot section of an 8/4 plank at the local hardwood supplier and I had enough to make the frame. This is precious material and I have a responsibility to make very careful and considerate use of it.

Here's a few pictures of the material, the first showing how it's natural color compares to the stained SYP:


Most of what I have to work with is near-perfect rift grain, though, as the above picture shows, the brackets have flat grain.

Some of my other pieces, now jointed and milled to dimension - I took the wood to the shop down the street and worked with one of their employees for an hour to process the pieces:


I've already started in on the layout- the first pieces I tackled were the main frame components:


The mechanical pencil lead is clearly visible on the dark surface so long as the lighting is sufficient.

Because the Wenge is leagues stiffer and denser than the SYP, it did not need to be as chunky. The original frame rails were 2.25" (50mm) by 5" (125mm) - I've slimmed these dimensions down to 1.75" x 4.5". The frame is still going to be stouter than it needs to be on structural grounds, however the aesthetic norm needs to be addressed as well. It's a compromise.

I found the original support brackets to be a bit on the rough side - the outer lines were not sinuous and there were intermittent flat sections in a couple of places, and they had been formed with little more than chisel and saw. I looked at a bunch of other battari-shōgi examples to compare their support brackets, and found that there was a diversity of forms. Thus, I felt safe in massaging the form a little to obtain something a little cleaner looking, while still keeping to a semblance of the original lines. I have made templates for the new pieces, and in the following photos you can see how the old and new shapes compare:



One key design issue were the main bench hinges. I fired up the SketchUp to explore the joinery. I told the museum that I would be stepping the quality of construction of the frame up a notch or two.

The points where the rear frame corners connect are the tricky bit. After some manipulation, I settled on a twin-tenoned construction with a lipped mitered return on top and a floating hinge pin 1" in diameter:


Notice the small curved section removed at the bottom edge which will allow the piece to smoothly rotate around the support ledge on the support bracket.

The twin tenons will also have root stub tenon, or mechi, which will serve to resist any tendency of the part to twist and to reinforce the tenons:


Here's the opposite piece which will be mortised:


The pin is to be a separate piece which I will glue into place. I considered machining the pin out of the solid frame piece, but I don't have access to such a large lathe (the ideal way to fabricate such a piece), and by using a reversible glue, like hide glue, any wear on the pin could be repaired by replacing only the pin. And the pin, for that matter, along with its mating socket (which will also be an insert) will likely last for a very long time as I am going to make them out of lignum vitae. The hinge should last, effectively, forever.

More to come...click here for part 3

2 comments:

  1. Looks like a great build..... I'll be following daily as usual.

    ReplyDelete
    Replies
    1. Ah, alas, I forgot to reply to you Woodjoint - - belatedly, many thanks for your comment!

      ~C

      Delete

All comments are moderated:

Anonymous comments will be deleted

Spam will be deleted

Comments containing links unrelated to blog content will be deleted