the Carpentry Way: French Connection 11                                                          

French Connection 11

    
A received a question recently concerning the applicability of this three legged bench - did people make these? Well, yes - here's at least one, a scale model:


This three-legged bench is really a convenient vehicle for the study of placing an inclined saltaire cross between a cross-beam and purlins, along the lines of this study:


In the last post, it appeared I had completed the drawing work on side 2, the second set of saltaire braces, a pair which have their front and rear sides plumb. Well, not so fast there young fella! While working to develop the brace's joinery details, certain things came to light in regards to the joint where the two pieces cross one another, and that caused a back step in the process.

The first set of braces, on side 1, I had made as square sections, 1.125" on each side. As one might expect, those braces, as they have faces flush to one another, fit together seamlessly when they are the same size each. When it came to side 2, I followed along with that pattern, making the braces 1.125" on each dimension. It makes sense to use the same section of material for all the braces, or so I thought. What happens though, when you use the same size section for each brace on side 2, is that the crossing point between them ends up with some goofy little joint interfaces. This is something I hadn't noticed on the previous drawing go-round (three years back) on this piece.

I'll show you what I mean, using my prior drawing for the trépied établi:


Now, zooming in on the front of the crossing, and looking at the lower intersection, you can see that they don't quite meet spot-on, which leaves a slight little barbe ("beard") indicated by the arrow:


Rotating around the connection, a similar situation occurs at the upper rear intersection, though here the barbe is very slight:


In order to eliminate those barbes, I had to reconsider the dimensions of the sticks. After some thought, I decided to make the plumb measure of the braces equal to the section height of the tripod top beam pieces, at 1.5":


With this change, which was easily accomplished in a 2D to 3D development, the front face's barbe disappears:



Not all was well however at the back - there was still a tiny barbe:


This barbe is a compound joinery effect, as the two sticks each have a different slope. The only way to eliminate this tiny barbe, besides ignoring it of course, leaving a less-than-crisp or fudged fit, would be to change one or both sticks in their section thickness. I decided to change one stick, which made it 1.128" instead of 1.125":


None of these issues revolving around the fit of these parts as the intersection was apparent from the text, and it was difficult to know exactly what was intended, as the drawing of the tripod bench in perspective does not show the meeting points for this side. So, all i can do is discover the issues and try and find the best solutions I can. I'm grateful for the 3D as otherwise I don't think I would have been able to discover these issues so readily from the 2D plans. Indeed, I imagine that the second tiny barbe, as shown a couple of pics above, would have appeared in 2D layout as a tolerance error (it's about pencil line thickness) and I would have just connected the lines - fudged it - and the result would have been a gap in the fit or a not-quite fit.

Anyway, these barbe'd comments, ahem!, are but a warm-up for bigger fish to fry in this project. By far a bigger concern to me is how I am going to put the bits together with joinery.

Here's a look at the older sketch of this project, where you can see the prints (outlines) of a post and two braces (one from side 1 and the other from side 2) as they converge at the top surface of the beam:


Clearly, there is too much going on in that space. While a tenon from brace set 1 (to the right) emerges into clear territory on the top surface of the beam, such is not the case for the brace coming from the left side, from pair 2, which largely occludes with the traced outline for the post.

Here's a view of the same thing from my current drawing, in which I've drawn the post's tenon and the beam mortise already, and you can see where the brace traces emerge on the beam's upper surface:


I can't see any way I can put a through tenon in there coming from the brace - and the text indicates no tenon there, however whether the text shows a joint or not, I have a hard time taking the text seriously. After what happened with the 4-legged Mazerolle tréteau project from a couple of years back, where several mortise and tenon connections were indicated which later proved to be impossible to assemble, call me a skeptic. All tenon depictions in these books I take with a large grain of salt. In this instance, I agree though that no conventional through tenon seem possible in that location.

Take a look at this picture from Delataille's work, which shows a through mortise and tenon connection for the brace:


I'm doubtful that will go together as illustrated, unless some of that new rubberized wood is involved, and that is even presuming that the crossing point of the two braces is formed not from a lap but from three pieces, mortise and tenoned.

Examples of impossible connections abound in Delataille - here are a couple more:



From the maquettes I have seen, these sort of multi-legged saltaire-braced tables invariably have nailed connections. The French aren't that preoccupied with joinery. In some models you can often spot the odd place where a nail has rusted off and some little portion of a brace has fallen off at some past point in time.

Examples:


I don't see any pegs or other joinery telltales.


Here you can see the nailing fairly clearly:


Can't forget this one, one of my favorite little pieces of insanity:


Every time I see it I laugh and wonder how many hours that took to make!

I guess I would rather avoid using nailed or glued connections on this piece, but am seriously doubting how I might realize that goal. It might be unachievable.

Thanks for the visit, and we'll see you next time.

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