Tuesday, February 5, 2013

French Connection 9

It's been a while since I updated this series - a bit over 3 years in fact. After my various frustrations with drawing dormers in the 19th century Mazerolle book Traité Théorique et Pratique de Charpente, I decided to put the French carpentry drawing study on the back burner for a while and lick my wounds. If you do a search under the label 'French Carpentry Drawing' you will see where I have been.

Having taken my ginseng and multi-vitamins, done some stretching, and am feeling well-rested, I am re-engaging with the material. I decided that I will tackle the 3-legged joiner's bench, a project I first mentioned on my blog back in 2009, in a post entitled French connection, Part Deux. Here's the piece, as shown in perspective in the book:

The camera angle I used produced a photo which makes the drawing look a little distorted, though the sketch in the book does seem to exaggerate the view of the rearmost beam, tilting it up towards the viewer.

I worked for quite a while on the developed drawing to solve that particular piece, and in a post entitled French Connection 8, I shared my completed drawings - here's one of them, albeit with one of the brace pairs hidden from view for some reason:

That was three years back, and when re-entering the maze, I find that while I know my way around a bit, there are lots of places where I have to find my way again, often by following blind alleys I know I've explored previously. By another analogy, it's like some of the paint stuck, but a bunch fell off. Hopefully in the next round I can get more paint to stick to my feeble brain. The eventual goal, as far as I am concerned, would be to reach an understanding and facility with the method such that I could just sit down and draw the whole thing without doing too much head-scratching, and then, three years later, could do the same thing without recourse to my notes or having to re-study. I'm talking about soaking in the knowledge to the point where it becomes second nature, and I can tell you that I am a long way off that with this French stuff!

To recap a bit further, and provide context, there was a fairly demented Mazerolle sawhorse I studied, drew and built a few years back, in which the purpose of the exercise was to place scissor braces between 'hip rafters' (i.e., the posts of the sawhorse) which were rotated in various positions:

Some of the legs are rotated as a hip rafter would usually be rotated, i.e., with sides that are in a plumb plane, while other legs were rotated so as to be in plane with either the short end of the horse or the long side. Additionally, a set of scissor braces is placed between sets of main interior braces, which are each in a rotation relative to one another. In all cases however, the scissor brace parts join to one another with a mitered lap joint, their rotations being normal to one another - that is, their front faces are flush, like most lap joints.

I use this 'sawhorse' in my shop, and while it is plenty strong, it is not the most useful sawhorse as there is not much clamping surface available along the beams due to all the braces crammed in there.  I mean, the point of the exercise wasn't to just make a sawhorse, but to study a layout problem, or étude, and it certainly was a boot-full of that. That it is of some use at all is an added bonus of sorts, however the ultimate usefulness of a thing that absorbs hundreds of hours of my time and energy is a factor to be considered when deciding whether to plunge into the pool or not. I'd rather come out at the end of that swim with a piece that is a complete structure, useful for something, even if only decoration and the joy/pain of learning.

With the three-legged bench, or trépied établi, the posts are all in the same rotation and it is the scissor brace rotations that are manipulated. I'll show you what I mean-  let's look at the three sides of the bench - take a look at how the scissor brace pieces are rotated, relative to one another and relative to the bench top and plumb.

One - the braces are in plane with one another:

Two - the braces are each rotated to have two faces plumb:

Three - the braces are rolled to that their upper faces meet the top beam flush:

In the above 3 sketches I've removed the development traces, which are rather numerous, to give a clearer view.

I have contemplated building this piece a few times over the past few years, but have talked myself out of it each time. My objections are two-fold:

  1. a three-legged joiner's bench would not be a useful thing to have in my shop
  2. the ill-fit between the leg and the beam bugged me.

By #2, above, I refer to this - the red bit that sticks out to the side:

I have tried solving that problem in a variety of ways, including rotating the leg, making the leg a parallelogram in section, feathering the face in to the beam arris with a twisted surface, etc. All those other 'solutions' are problematic for various reasons, and rejected.

So, how have I now overcome those two objections? Well, I have decided just to live with #2, and will make the piece as a coffee table with a glass top, so I don't have to worry about its questionable functionality otherwise.

For the past several days I've been devoting my spare time on a new drawing of the trépied établi, and have nearly completed scissor brace set 1:

This sketch gives a good idea as to how many traces associate to developing just one set of braces.

A view from the other side:

I'll keep pecking away at it and hope to have the drawing work done by the end of this month. I've got other projects going on at various fronts, and this is a lower priority. I do enjoy re-engaging in study, even if my brain feels like its going to melt sometimes.

Thanks for visiting! Comments always welcome, and if you have tried to comment and it won't go through for some reason, try refreshing your browser or using a different browser. And if that is to no avail, please send me an email to let me know. On to post 10.


  1. Hallo Chris
    I can not say very much about design of sawhorse, because You are so far ahead, but if
    You start making it ,what kind of tools are You using to carry angles from computer to the wood (lets say that in computer You have a line 37,61 degrees to another or whatever and this angle should be drawn to the wood). Is there any special technique ? I have seen Japanese are using rather thin squares in marking process(have no idea how they keep them precise-from dropping to the floor and get damaged etc ?), but it would be more interesting to know more about it. Probably angle measurement should be avoided and replaced with two 90 degree straight lines with certain length and needed line comes with help of the lenght of these lines. If You understand, what I mean ?

  2. Priit,

    good to hear from you. I have various tools and techniques for laying out angles. I use a framing square of course, and various bevel gauges, along with straightedges and rules.

    A traditional method is to draw the piece at some scale and then set a bevel gauge to the drawing for the required angles, or draw at full scale and place the sticks directly atop the drawing and transfer up the marks from paper to wood.

    I didn't follow that full scale layout method for the sawhorse I did previously because I made the thing in my kitchen and simply didn't have the floor space to do the drawing. So, I used my calculator to work out the trigonometry, giving me the angles, then set the angles using framing square and bevel gauges.

    With this project, I'll probably do a full scale drawing for at least some portion of it. The disadvantage of a full scale drawing crops up in the odd place where the line produced by the drawing is short and the potential for inaccuracy when applying a bevel gauge or direct-transfer of tick marks is there. In such cases, i often calculate the true angle and then use my framing square. also, if there are angles which appear in several places, I will set the angles first on a pitch board which I can return to later and use to reset the bevel gauge.


  3. Hey Chris,
    I'm glad to see you back at the Mazerolle! My own carpentry drawing exploration has been on the back-burner as well, but your new series may inspire me to give it another look.

    Good luck,


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