Thursday, January 29, 2009
The French layout challenge
What you see here is a kinda complicated French sawhorse. At first glance, it may appear ridiculous to some - what possible point can there be in constructing such an object?
Strictly speaking, as far as sawhorse 'requirements' are concerned, this unit is clearly beyond any performance need. As the description for the piece reads, it is "très résistant". Much more than that though, this sawhorse is a vehicle for study of roof layout, particularly the layout of hipped roofs with diagonal bracing. As an example of roofwork featuring this sort of bracing, I attach a picture of one application, a Mansard roof:
There's more to this sawhorse than meets the eye at first. Take a look at the legs. You will see that one pair, diagonally opposed, are rotated so the corner of the leg meets the corner of the floor plan of the horse, and the other two legs are rotated 45˚ along their axes, similar to the way a hip rafter is commonly oriented (i.e., the side of the rafter is aligned plumb to the floor). Even the pair that are rotated so their corners meet the floor are subtly different from one another - one being aligned to the long axis of the plan, and the other aligned to the short axis. To this melange of leg orientations, we interconnect x-braces, and then even inter-connect x-braces between cross braces. It's quite insane! I get dizzy just looking at it. The layout problem condenses into determining relationships of positions between parts, as there isn't wiggle room between pieces, with so many crowded into the same space. To complicate it further, the pieces are all through-tenoned to each other, which means the shapes of the tenons vary and the mortises are shaped to suit. Even the cut out of the mortises will be difficult, given their shapes.
Why tackle something like this? Can I sell it for big bucks? I doubt it, and that is most certainly not the point. While some may question the value of doing anything if there isn't a pot of gold at the end, the study of this sawhorse, and the successful incorporation of the layout technique into my repertoire will lead to something quite wonderful: to be able join a piece of wood, at any rotation and orientation, to another piece of wood, at any orientation or rotation. This is a powerful possibility, and opens up wide design possibilities, as does any new capability. There is endless material that can be studied through the 'vehicle' of the sawhorse, and I will cover versions of Japanese sawhorses, which are complex in a different way, in subsequent posts.
I want to make this sawhorse, but I can't make it yet. Despite nearly a hundred hours of study, and multiple re-draws, I still do not understand this sawhorse completely. I'm getting there though, and expect to get to the construction phase within a month. Then I expect that the first time I make it there will be some goof-up, something I didn't see quite understand. If I don't understand a drawing, then I draw it again and again until the truth is gradually revealed. If I make it and something doesn't fit right, then I make it again until everything fits. It's a bit of a 'brute force and ignorance approach', more dependent upon perspiration than inspiration, but that is how it goes sometimes. Sometimes I wake up in the morning suddenly understanding what was a mystery the night before.
Here's what the drawing looked like a while back, to give you an idea of what is involved in determining the cut lines for each piece. This drawing is about 80% complete, and has a few problems, so I will be drawing it again. I need to rest a while and let some stuff soak in. I'm also in communication with a campagnon du devoir to help understand some of the, er, 'sticking points'. Not the best pun, but worth a try, no?
If you click on the drawing, it will become a bit larger and clearer. Welcome to my dream.
Okay - interested in reading about the actual build?
Go to part I
Want to skip the build and see how it turned out in the end? Click here.
For the next post on the subject of French carpentry in general, click here.