Now, it wasn't my intention to be devoting two posts to each of the drawings in the Mazerolle book, however, such is the case. I hope no one is falling asleep. Anyway, here we are again, with the hipped dormer problem detailed in the previous post:
Yesterday I mentioned that the drawing in the book for developing the view of the noulet was screwy, so I employed a different technique to produce the pieces. That method led to a perfect result - here you can see how the foot of one of the noulet (in yellow) meets the plate as it should:
My thought, always willing to give the benefit of the doubt, was that there must be some sort of new concept I was unfamiliar with in the Mazerolle drawing, and thought therefore that the best way to figure it out would be to place the completed piece, which I knew to be correct in shape and dimensions, back onto the drawing and reverse engineer it, as it were, to see if I could crack the code. Seems like a reasonable way to proceed, no?
Here's a view of the developing drawing portion, which I situated directly below (ie., in plumb) the actual dormer so as to easily transfer lines roof to floor:
First off, here's the developed drawing portion as shown in Mazerolle:
On the left side is the end portion of the plan view of the hipped dormer. Fig. 2, on the right, is supposed to show the development of the noulet. The piece LMQR is one of those noulet, KNPS is the other.
The weird bit is the establishment of the height, which is length AB. Trouble is, that length is not the same as the actual height of the dormer off the plate, but somewhat shorter. It should be the height off the plate as far as I'm concerned. I used a compass set to that measure AB anywayand looked around the drawing at a few likely places to see if I could find something the same, all the while doing my best in a carefully reading and re-reading of the text in its somewhat inscrutable 19th century carpenter's French. The best I could figure it, length AB was supposed to be the same as the length CE in the following portion of the drawing:
This section is the remainder of the plan view, and shows the noulet looking down from above. Thus length CE is the distance in plan from the foot of the noulet to their heads.
That use of CE as the height AB wasn't making sense, but what the heck - let the reverse engineering begin:
You can see that my rendition looks pretty darn close to the text. I have brought down a copy of one of the 3D noulet, and placed it on top of the plan. Trouble is, it doesn't quite match:
In the above picture you can see that the dimension of the lower face of the noulet, where it meets the plan, is not the same as the drawing. If I drop points down from the corners on the upper face, they don't met the plan at the right spots either.
At the foot end, the fit is also off:
So, I conclude that the method shown in the book on that section doesn't work at all to produce a correct part, though I am open to the possibility of profoundly misunderstanding the purpose of that section of the drawing.
One more detail - the bottom of that drawing in the text showed the means by which a stick of wood can be cut obliquely through its cross section to produce two of the trapezoidal noulets. Here's a focus in on that portion:
You can see two trapezoids touching at one corner. The lower one to the left side is the actual cross section from the 3D noulet which I know to be sized perfectly. The one on the right above is that produced by the drawing method shown in the text - not even close, either in width, height, or angle of cut. Look back to the Fig. two illustration a few pictures up, and see the parts labeled 'a' and 'b' with the arc swung between them. That is what I have reproduced in my drawing above.
Okay, setting that frickin' mess to one side, I went back to the main plan section of the drawing, where it showed another development for the noulet, one where the sauterelle, or bevel gauges, could be used to pick up the relevant angles. I set up my drawing in as close a representation to the one in the book as I could, then dropped the 3D parts down to see what lined up with what:
After a bit of fiddling, more than a bit actually, I was able to achieve congruence between the development in 2D and the part itself:
Trouble is, the drawing in the book is slightly misleading in how it shows things. Take for instance this picture of the cut at the top end of the noulet:
And this is what it actually looks like, note the difference in the form of the yellow trapezoid to the shaded footprint in the drawing above (and the other problems with the way the end of the developed leg looks in that drawing compared with the actual piece):
It's little things like that which can cause a lot of confusion when trying to sort out the connections between pieces and how something is supposed to look. Besides the error with shading the footprint, the book shows some erroneous projection lines. Things like that can lead you down dead ends for long periods of time. It's frustrating.
So, I know more than a few readers out there might be laboring trying to make head or tail of these drawings - it isn't the simplest stuff to get your head around, and that is why so many avoid it. Despite that, I am trying to show as best I can however that the Mazerolle book again seems to be, well, totally screwed up. I hope that you don't need to understand the drawings I have shown to be able to see that there are some problems there. If it wasn't for the luxury of being able to make the parts in 3D, then compare them with the drawing, I really doubt I would be able to sort these issues out.
There are so many pitfalls in following the drawings in the book.
So what to do? Should I keep going in this quest to draw so many of these pieces? It's a major uphill battle, and after such a struggle, probably 20 hours work on the simple hipped dormer, I might anticipate that there will be drawings ahead I won't be able to figure out even after many hours. Is it worth it?