Friday, January 30, 2009

The French Connection, part deux

Yesterday I showed what the sawhorse Olympiad looks like, and today we look at the three-legged race: the Trépied Établi, or three-legged joiner's bench. The perspective drawing is a bit odd, as it appears to show the rear-most cap beam rising up jauntily, whereas it is in fact horizontal like the other two beams to which it connects. The right leg looks like it is more sloped than the others, when in fact it is the same slope as the one to the left. I think the intention of the artist was to show what the mortises in the top beam looked like in that particular spot, though, puzzlingly, in other spots he omits to illustrate the mortises altogether.

In the sawhorse mentioned previously, the braces are are normal in orientation to one another where they cross, and it is the legs which are in a variety of rotational positions. Here, in Trépied Établi, the situation is reversed: the legs are all oriented in the same way in terms of rotation and slope to the floor, while the braces cross in a variety of rotations. The braces by the way are called "Les Criox de Saint André" (St. Andre's Cross), and the set facing us in the drawing is oriented with the two pieces normal to each other. On the left side, the braces are 'faces aplomb', meaning that each brace is rotated so its side face is in plumb. Then there is the set on the right side, "faisant lattis aux chapeaux", meaning that the braces are rotated so that their upper face meets the top of the beam (the cap, or 'chapeaux') flush. To the left is a drawing of this joiner's bench I did a while back. Again, I have at least 100 hours into studying this piece, and again, the drawing shown is incomplete and there are a couple of mistakes (at least!). In this version I haven't illustrated the Saint Andre's Cross for the right side. That in fact turns out to be the difficult one to figure out. The braces which are oriented plumb are the 'easiest', and the other set is, for lack of a better descriptor, 'medium'. I am actually at about the 90% mark with this drawing now, so it's getting pretty close.
There are yet further 'bracing possibilities', and in fact there is a second drawing set later in the book showing one of them - the same bench, in which one brace is rotated in plumb to the floor, and the other one crossing it is rotated to bring it's upper face flush to the top. Other configuration and combinations of course spring to mind. I've been thinking about designing a 5-sided version, a Cinqpied Établi, each of the 5 sides with a different combination of brace relationships, and putting a glass top on it. It would make an interesting dining table, or perhaps in a shorter version, as a coffee table.

This drawing starts to get pretty congested with projection lines when you draw the whole thing out, like a bunch of angry wasps swarming something, so I have been drawing a bunch of separate versions, each showing only one set of braces. I feel like I'm closer to solving the layout issues with this bench than with the sawhorse, so I may be making the bench first. Certainly the top beam assembly and legs I could start on any time. I need to get some wood - I might get African Mahogany from the window and door manufacturing place down the road for a final version, and perhaps some Yellow Poplar, which is inexpensive for the prototype. Again, the first one I make is likely to have some 'issues', so I would be smarter using some inexpensive material for that go-round.

Just for those who may be wondering about the drawing business - "what's the point of that?", you might ask. Well, the only way to figure out how to cut - uh, wait a minute, not the only way, just a very elegant way - to figure out how to cut the various pieces where they intersect is through creation of a developed descriptive geometrical drawing. This method of drawing, in fact, was invented by Gaspard Mongé in the late 1600's, a Frenchman, and the subject of a future posting. Carpentry is forever in this mans debt, though many carpenters the world over have never heard of him.

Japanese (and Chinese) traditional carpentry does not make use of diagonal bracing to such a significant extent, for various reasons, so my study of French brace layout is a means of filling a gap in my knowledge. I am a strong believer in the benefits of triangulation, except for, uh, the interpersonal kind.

2 comments:

  1. Hi Chris, Great stuff. Was wondering in Monsieur Monge might have been taught by some monks? Seems like I heard that the monks of the medieval era knew something of this.

    My instructor has taught us this method of graphic representation. However we have not quite gotten to this level. We have graphically represented two pieces oriented at any angle that intersect. After working with groundlines of planes it was difficult to then add the "skyline" (a term we came up with).

    To your point about the only way. Yes someone could possibly cut this from certain design programs as a crutch; but they would certainly have a difficult time with it without knowing what was behind it. And if the pieces of wood get bigger for some unique framing...well than it seems the graphics are imperative.

    Great blog man. thanks, mo

    p.s. I started something like this about a week ago. I am going to post all the lessons and models we have learned in chronological order. It is still in its infancy. I probably have about 18 more drawings to add with an additional angle to find in each one.

    http://raisetheroofhigh.blogspot.com/

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  2. Hi Mo,

    checked your blog out -more power to you! It's a valuable thing you're doing.

    Monge did not, as far as I know, learn his methods from monks - he was more of a mathematical genius and developed new insights. Definitely more to come on that topic later.


    Chris

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