Tuesday, April 27, 2010

French Connection 11

Previous Posts in this Series:

French Connection
, French Connection Part Deux, French Connection 3, 4, 5, 6, 7, 8, 9, and 10.

I decided to explore some of the drawings in the Delataille work to see what was what, and started looking at some pieces on plate 15, which included a series of sub-sections of framing with through-tenoned parts. Here's the plan view drawing for one of them:

Now, I'll hold off for the moment showing exactly what this drawing is meant to depict, as I thought I'd share how I use SketchUp. My strategy is to draw the 2D development, then superimpose the parts on the drawing and transfer the marks needed to define cut lines, mortises, tenons, and so forth. This is using SketchUp in an unconventional manner, but it is a method very similar to the standard practice of both French and German traditional carpentry drawing, where the drawing is made full scale and the wood placed directly upon or above the drawing and the marks transferred. SketchUp is a modern tool, and I'm adapting it to use in the manner of traditional drawing practice.

Here's one section of the plan view that is up for a transfer to a corresponding stick of wood:

Note the location where the two arcs swing through the stick outline in gray at the left lower section of the picture. Where these arcs meet the lower edge of the stick, they are 'reflected' back across the stick, the lines at 90˚ to the length of the stick. Notice the area on the stick with the 'x' marked on it - this is the outline of a mortise.

Here's a closer-in view of the area, and I now have made marks, out and away from the stick outline, showing the intersections of the various lines I need to transfer:

Now, rotating around to look from another vantage point, the section of wood is placed atop the plan drawing and lines are transferred plumb up the stick. The plan drawing, in this case, is showing the top surface of the stick, so the marks off the plan need to be taken from the floor to the stick's upper surface:

When all the lines have been transferred onto the stick, I can connect the dots and define that mortise:

The same procedure is repeated for the other parts and surfaces needing marks on them:

The stick at the top and the bottom of the drawing, connected it would appear at one end, are in fact two copies of the same stick, just positioned so as to transfer marks to one side of the stick or another. The stick in the middle is a brace.

Once all the parts are done, I can 'assemble' the piece in 3D- here's the finished construction:

A couple of points:

-the post is rotated at an angle to the beam (not 45˚ but closer to 50˚) and the beam and brace tenons pass through the post at an offset angle. That's what the drawing is all about.

-this piece could not be assembled as drawn! There's no was that a beam and brace, tenoned together, and each through tenoning into a post, could assemble to the post. This could be done is the tenon shoulder on either the beam or the brace were trimmed to a taper.

So, just like Mazerolle, the Delataille book shows constructed items that are impossible. Perhaps the point is to show individual examples of various connections, I don't know.

Here's another example, first in plan:

This one is an irregular hip rafter problem, with a jack rafter and a cross-wise purlin which both tenon through the hip. Interesting (to me anyhow!).

Here again is the step of taking marks right off the plan drawing and transferring them to the sticks:

The purlin is seen at the bottom of the drawing, while the jack is angled to the left above the purlin and is in two sections.

Here's the finished construction:

The purlin is a continuous piece of wood, while the jack rafter is supposed to be in two sections, each tenoned into the sides of the purlin. Still, unless the crossing points of the purlin and jack were a good distance away from the side of the hip, it would be very hard to assemble this construction. I'm following the drawing in the Delataille work quite faithfully in terms of the relationships between parts.

Another view:

So, As I have noted previously, it seems like these early French layout books tend to show a lot of stuff which would trip up the unwary. There are good lessons to be gleaned however - for instance, while the above-constructed hip rafter assembly is not really possible to assemble, the drawing method does provide techniques for through-tenoning either jack or purlin on it's own through a hip rafter, and that might be desirable to do in certain circumstances. I can see some applications in traditional Japanese roofs with their hidden roof/structural roof system, for instance.

My study is on-going, as this is all about the journey and the lessons picked up along the Carpentry Way. Thanks for dropping by today.

1 comment:

  1. Posting from my phone. So I will be brief. I've used this method for
    irregular saw horses. I'm always gettin tripped up as to which lines are up
    and which lines are down.


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