Monday, November 2, 2009

Tréteau II

I will have to wait until Wednesday to do the jointing and planing at the shop down the road, which is fine as it gives the recently-cut Canarywood a little more time to move and unstress if that is what it wants to do.

I started working on some of the developed views today, starting with the long braces, or croix de Saint-André des liens mansards- here's that section out of the text, and once again I apologize for my photographic clumsiness and the slight blurriness to the image:

Note in the drawing, in the elevation view at the upper section, how the two mortises (which are for the interior x-braces) are arranged on the face of the brace (the mortises are however not transferred to the developed view) - the illustration can only be showing the inside face of the braces, as they are laid flat on the ground. Given that fact, the brace which is developed can only be the left hand one on the sawhorse (given the side which the view is produced from), and the developed view is also of that same brace.

Now, I drew the brace development on my drawing by following the method of the drawing in the text as well as I could. To be sure, I don't fully understand every line on the text's drawing quite yet, and I am also, it must be emphasized, not able to simply copy the drawing. There are some differences in the relative spacing of some lines in relation to one another between my drawing and the one in the text, attributable to differences in parts sizes and angles, and thus it is my job to puzzle out why a given line projects to a point. Most of it is not too difficult, but there are some lines that remain quite baffling for the time-being. Anyhow, after a bit of work I had succeeded in drawing a similar picture of the brace to that in the text:

All was looking fine, I thought, and so I decided to extract the same component from the 3D drawing, rotate it flat to the floor and place it next to the 2D version to see how they compared. The idea being to more fully understand the 2D layout. Then came the surprise:

Clicking on the image will enlarge it. The developed view of the brace in the textbook is illustrated incorrectly - it is in effect a reversed or mirror-image of what it should be. You will see, if you mentally rotate the 3D brace at the top of the above drawing around, that no matter how you flip it (and there are only two possibilities, as it can't be flipped end for end), it simply cannot match the text's drawing. Curious. In the above drawing I have the barbes (the 'beards', or thin slices at the ends of the stick) so they are on the same side as the 2D drawing. Clearly, the lap joint is backwards and the slope of the barbes is opposite in this case. If you rotate the stick 180˚ to it's opposite face, then the slope of the lap notch is correct but the barbes fall on the wrong side, amongst other problems.

The brace as illustrated actually looks much like the right side one of the pair, however the right side one meets a 45˚ rotated leg, so the lower tenon and adjacent tenon shoulder would not be the same arrangement. So that is not what it is either.

It's not big deal- I will simply redraw the 2D sketch to correct it, however I am left again wondering how to account for the 'error'. Is it a deliberate mistake on the part of the original illustrator, or did he simply have it mis-oriented in his head? One would think that if the drawing was actually used to produce the piece of the horse, this error would have been discovered. One of the commonality of the ways which the French and Germans employ layout is at full scale and by superimposing the actual parts atop the drawing and transferring marks to the actual sticks. If this were done with the drawing as it is shown in the text, surely someone would have discovered the problem? Maybe it is a deliberate mis-drawing for some reason.

It's hard to discover the answers to those questions, so I will plow onwards and see what other sort of trouble I can get into.

-- > Go to part III

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