Tuesday, June 30, 2009

French Connection 4

This is my second post today, so if you are just checking in you may wish to take a look at the archive for my previous post.

It was about 6 months ago that I first started intensively tackling some projects in a 19th century French carpentry drawing book I have by Louis Mazerolle. One of those projects, the tréteau, was first shown in this blog back in late January, in a post entitled The French Layout Challenge. This post, though of a slightly different title is a continuation of that series beginning in January. Subsequent posts have been French Connection, Part Deux, and French Connection 3. New readers, or those, like me who find their memory occasionally betrays them, may wish to read those posts first before proceeding.

When I last left off in this series, I was somewhat impatiently waiting to hear back from a campagnon who had said he would help me with the areas of the drawing that were giving me trouble. Well, eventually I'd gotten to a point where I had pretty much given up on that fellow, when just last week I got a message from him apologizing for the delay, and that he hadn't been able to make much of the drawings, text and photos I had sent him and let me know that he was going to France for the summer and would be picking up a copy of the Mazerolle book and would be better able to help me from that point.

That was great news. Then it occurred to me that in the meantime, now that I had gained some facility with SketchUp, I might be able to render the parts of the drawing that were puzzling me into 3D, which would be much clearer a means of showing the campagnon exactly what the issues were. So, over the last few days I have been devoting a fair amount of time to re-drawing (this must be the 6th time overall now) the tréteau. My intention was to try and use SketchUp as a 2D platform, where I could use the development techniques to locate the positions and shapes of the parts, then replace the central plan view with a 3D view.

Here's a look at how the overall drawing looks, not quite complete but mostly there, with all the traces still in view:

While it might look to some as some kind of spaghetti junction gone mad, it's actually pretty clear once you know which line is going where and more importantly, why.

Here's a closer view of the tréteau, not quite complete, showing how I have developed the 3D from the 2D plan view:

Well I've gotta say, this SketchUp has really helped me out a lot! The reason being, is that once I have completed a 2D development, I can construct it directly (that is, virtually) by raising the 3D view from the plan. If the points from the 2D plan and its developments connect to form planes (which is what you want) in 3D, SketchUp shows that by automatically filling in the planes. It's not that I necessarily want the planes filled in, as in many cases I don't - it's the fact that it confirms that my 2D development is correct. And once I know that a given part is correct, that is one less thing to be uncertain about and the process can roll onwards.

It goes further though, the 3D, in helping me out. There were concerns in my mind that I wasn't seeing the 2D correctly in some views, and that the legs were surely going to interfere with one another in a couple of spots under the top beam of the horse. Developing the 3D has shown me that I was correct in these suspicions.

I have also been able to clearly establish that the original drawing of the sawhorse in the book is in fact incorrect in several places. Whether these errors are as a result of original error or miscopying, or are deliberately there to keep the student on their toes, I can't say. The main thing though is that I'm not hung up on these little issues any longer - the book, wonderful as it is, has a few minor glitches is all.

Another aspect of the original drawing is that a fair number of lines are in fact omitted, and I think this makes sense given how many lines are eventually required. I think that L. Mazerolle left out lines where it was presumed that the development solution was 'obvious' (perhaps to him and his students, but not always to me!), or where, as I have discovered, he is using the same method elsewhere on the drawing and only chooses to illustrate it once. Further, there are parts of the drawing where even after looking very closely with a magnifying glass, I have been unable to make out exactly what is happening at certain places. At other ares of the drawing, I have been unsure whether certain locations where a lines meet are in fact intersections or are simply lines that end up close to one another. There are a lot of places where the drawing is quite bewildering, and given my poor command of 19th century French, apparently very tough even for French speakers today, the text is not of much help even though I have translated all of it that pertains.

In the classroom, were Mazerolle to be teaching the layout of something like this, he would more than likely have an example already made, and having the actual object there while working on drawing it, is very helpful indeed. Now with the capacity to develop 3D views closer at hand, in effect I do have that model to refer to. In some cases I can draw the 2D, develop from that a 3D assembly, and then actually remove the part in question from the assembly, rotate it around and down to be flat on the floor, so to speak, and then I can superimpose it over the 2D and check things out. That technique has helped me resolve several areas of confusion and bewilderment on the drawing, and I'm happy to say that I have managed to now complete the drawing of the tréteau! I won't actually be needing the campagnons help after all it looks like (though we'll see about that - I haven't made it yet!).

Here's the 99% complete tréteau drawing:

The above drawing, as well as the one to follow, are in the large size format, so if you click on them you will get a better view.

As a final bonus from this application of SketchUp, I have been able to readily re-scale the tréteau to be more useful to my needs. The example in the book scales out to 90cm high (@35.4" tall). I prefer sawhorses that are lower myself, and my other current sawhorse, the irregular-splayed Japanese style one I detailed in the series of earlier posts entitled "Irregular Situation", is 24" tall. I was able to scale the 90 cm tall tréteau down to 60.94cm, and now I have been able to re-measure the parts, and thus it will be easier to re-draw the horse (yup, I'll need to draw it at least one more time) knowing how big to make all the bits so they work in a more compressed space. That means, for example, that the legs of the tréteau are going to shrink from 8cm (@3.1") to 5.8cm (@2.3") in section. Here's a look at the original, along with the scaled-down tréteau:

I'm feeling quite elated to have cracked the code of this drawing at long last. I must have hundred of hours in now on the drawing work, and it's good to not have to pull any hair for the next while at least. This realization of an accurate model also saves me at least one round of trial and error in the construction process, as previously anticipated, since I am now very confident that the layout will be correct and I can cut pieces hopefully without wasting any wood. The assembly of this horse is likely to be pretty tricky, so at this point the unresolved issues concern the tenons on various pieces, and how their shape will affect the assembly process. In many cases the tenons appear to diminish in size by about half from root to tip. The above drawings do not show all the through tenons yet, nor have I performed the diminishing-down to some of the exposed tenons.

I posted twice today as I am going to be away from my desk for about a week. When I get back to the keyboard, I can return to the lantern project, and of course the next installment in the kō-ko-gen-hō series. I hope my readers in the US have a great 4th of July, and those in Canada a happy Canada Day on July 1st (and my apologies to readers from other countries as to my ignorance of your holidays).

I will have net access, so any comments posted will be receive a response.

à bientôt

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