Wednesday, November 25, 2009

Seeing the light again

To celebrate my 151st post (it's as good a number as any), I thought I'd break the unrelieved monotony and bleeding eyeballs of all the drawing that have characterized recent posts on the Mazerolle Tréteau.

A few weeks back, I managed to take the Shrine lantern I built (see the "First Light" build thread) out to a nearby reservoir, which made a nice setting for taking some photos. It seemed like a good idea to have an intermission and show a few of those pictures now, especially given the somewhat poor pictures I had taken of the assembled piece at the conclusion of the build.

Just walking along a path..


A few steps closer:



For a different perspective, consider what a squirrel might see:


And one last one, with some disheveled fellow standing next to it - the idea being to give a sense of scale to the lantern:


In closing, I would would like to wish my US friends a wonderful Thanksgiving holiday!

Sunday, November 22, 2009

Tréteau VII

Did I actually end the last post with the comment "the end of the drawing is nigh" or something like that? Silly me. Such optimism and naiveté.

This is the 7th post of a thread devoted to the construction of a 19th century French carpenter's sawhorse, of, uh, a somewhat complex design. This sawhorse is a vehicle for roof carpentry study, and that's why I'm tackling it.

I thought the legs would be relatively straightforward to lay out, however they have proved to be rather difficult - even brain-melting to deal with. It doesn't help that once again I find the original illustration in Mazerolle's book to have further errors. Now, I'm with the reader who suggested that the errors are likely due to the work of the engraver of the printing plates, however I'm not so sure that is the issue in all cases. It's one thing to connect a line, especially when it is clustered amongst many lines, to the wrong spot. It's quite another to depict a part as a mirror image (and an impossibility), as I mentioned several posts back in the case of the development of one of the long side braces.

Now I have found a similar 'mis-drawing' as I work on the leg development. This was a part that looked wrong months ago when I was working on it in 2D only:


This is a view of the narrow end of the sawhorse, showing the development of the left-side leg and one of the Saint André cross pieces. Note the orientation of the tenon on the top, in both views, and consider how the tenon is supposed to be cut so as to be in line with the top beam. Note the single mortise on the face of the upturned piece at left, which corresponds to the tenon of the narrow side Saint André's Cross member. The illustration omits the mortise for the other Saint André's Cross member which connects further up the leg. The undeveloped leg to the right of the pair shows the mortise for the long side brace illustrated lower down.

Anyway, the illustration seems to show an impossible tenon on top of the post. It shows the tenon rotated 90˚ out from where it should be. Hmm... initially I thought I was merely seeing things wrong and had left the issue aside while I drew other parts of the sawhorse.

Now that I am back to working the details of the leg layout, in round 17, punch-drunk as I am, this issue arose once again. I was partway through drawing the tenon, 2D into 3D, when I realized that the tenon orientation was simply wrong. NFG. I dragged an existing 3D rendered leg out of the horse and laid it down next to the one I was constructing, just to double-check:


The wood-colored leg at the left is the one pulled out of the 3D drawing of the horse, while the one in white is the one I'm developing from 2D. You could mentally superimpose the white leg right on top of the plan if that helps. Note the location of the mortise again lower down on the leg (for the long side brace tenon) and the relative orientation of the tenon on top. Like the mirror-image long brace I found earlier, this is a curious 'mistake' -- was the engraver a heavy drinker, or perhaps thought it would be humorous to mess with the illustrations?

I moved past that issue soon enough when I accepted that there was simply another 'mistake' in the text - the legs which are oriented to the axes of the plan are reasonably straightforward to draw, and the mortises not unduly traumatizing to lay out.

The same cannot be said of the legs with are turned (in French: pied faces aplomb) in relation to the x-y axes of the floor plan. Here's the drawing supplied in the book for developing the mortises on the rotated leg:


Right near where 'Fig. 2' is written there is a shaded area that is supposed to be the mortise for the long brace in the lower portion of the leg. The vast majority of the lines necessary to construct the view of the full mortise, entry and exit, are missing from the sketch - just the skeletal outlines are provided to give the hapless victim the general idea. Trouble is, the mortise depicted in the illustration is the wrong shape, so the lines lead you into a quagmire instead of the hoped-for session of clear sailing. The tenon width is fine, however the top and bottom walls do not angle so sharply as the text illustrates, and thank god as the mortising would be a right pain if they were that shape.

Here's what the mortises should actually look like:


The smaller half-size mortise is the exit hole, as the tenon diminishes by about half as it passes through the leg.

I just about pulled my hair out trying to figure that one out, as the drawing in the text is quite misleading and it doesn't become apparent until you have drawn for a while, getting more and more puzzled. The problem is that the wrong lines are being connected to form the upper and lower walls of the mortise.

Thank goodness for the 3D, because it allows me to compare the piece, as it should look, with the 2D development. Without the 3D, I would have gone off the text's example, drawing the piece in a similar fashion and started cutting, only to find that the mortise would have been entirely wrong and the leg ruined after hours of work. Hopefully I can avoid such pitfalls, and the 3D is a big part of that.

Still, as I've mentioned, the essential skill for the carpenter to develop is the 2D drawing skill, which can be field-applied on a clean flat surface with ruler, pencil, compass, and string. Here's a short series showing some of the steps, going a little further from the 2D, in developing those mortises in the above picture into the 3D mortise. First, I raise lines to the thickness of the post on the uphill mortise, and connect lines down from that mortise opening to the half-size mortise.:


A peek around the back:


I raise more lines from the foot of the leg at the baseline, and construct a short section of the post, now with the mortise contained:


Next step is to deal with the mortise for the Saint André's Cross member. By the time that's done, the plan is a mess 'o lines. I'll spare you the horrow show.

Another curiosity I discovered in the past few days is that the two legs which are oriented to the plan axes are not actually square in shape. They are slightly rectangular by about 1/64". At first I thought I'd found another drawing goof-up on my part, but after checking carefully I found I'd connected all the dots correctly. One leg was rectangular in one direction, and the other rectangular in the opposite direction. Hmm...

So, I started a new drawing to see, experimentally, what would happen if I controlled the dimensions of the posts so they would be exactly 2" x 2". Well, you can do that, but the cost is that a bunch of other parts will end up being odd sizes. For example, one Saint André's Cross piece pair will be 2" wide, while the unit on the opposite end of the horse will be 1.98" wide. Same thing happens with the long side braces - 2" for one pair, and 1.98" for the other pair. I did a few rotations with legs to see how the geometry changed and discovered that the issue lies with the fact that the slopes are irregular in this sawhorse. I'm not going to try and explain in detail, because it is a bit complicated, but it was news to me when I discovered it. It's not possible with this method, using square-section legs in differing rotations, to specify the sizes of all the parts - most of them, but not all. so, one keeps the sizes at a set point in the elevation views, and the result is slightly rectangular legs and the interior x-braces end up being odd sizes in both dimensions (mine are 1.16" x 1.79").

Very fortunately, I left the legs just slightly oversize enough - about 0.02" - from the jointing and planing earlier that I have just enough wood, by just a couple of thou, to make the rectangular legs I now realize I need. Lucky. If the legs had been scant, I would have had to re-draw the entire sawhorse, and planed a bunch more off the braces. No thanks.

So, after experimenting with holding the leg sizes to 2"x2", I found it caused more problems than it was worth and returned to the original, er, 17th, drawing, and kept with the slightly rectangular legs, as it allows all the brace pieces to be exactly the same width. Reflecting further, and considering the difficulty I foresee of the cutting of the mortises and tenons with the French construction, I have to say I vastly prefer the relative simplicity and elegance of the Japanese method of re-shaping the legs to bring them into plane with the prismatic splayed form. While the hassle is there initially with the re-shaping, once done, and done accurately, the rest of the parts are relatively un-troublesome to cut, and the mortises and tenons free of extreme angles and barbes.

In a related vein, I wonder why the French have come up with all these methods for dealing with a rotated hip rafter when the backing cuts are not all that much of a hassle to make? Sometimes they do use a backed hip rafter, from what I've seen in the various books, but not consistently and I'm curious why, given the extra time and hassle of the tenons with their barbes and the often angle mortises that result. It doesn't seem worth the trouble, so I am curious to know what advantage was perceived by the other method.

Perhaps for the next sawhorse, a year or two down the line, I will breed, so to speak, the Mazerolle tréteau with the backed leg technique I figured out for the irregular splay Japanese sawhorse I already have made. That would be a pretty cool cucumber. For now, I'll forge on, and finish up the drawing in the next day or two and then can move on to layout and cutting by mid- to late-week hopefully.

Thanks for your patience and for dropping by. --> Go to part VIII

Wednesday, November 18, 2009

Tréteau VI

Still drawing....

Pffft! It's endless, or seems that way some days. I've had a few sessions of one step forward two back (my favorite game, after Sawing for Teens), however I am now complete through the stage of drawing the short side cross braces (the Saint André crosses) and the interior x-braces. All that remains to sort out now are the legs, and two of those are identical to one another, so I only need to draw developed views of three of them. So that's 'just' three parts to go and I'm done. Bwa-ha-hahahah - I'm not going to make any assumptions about smooth sailing however, as I seem to find innumerable ways to make mistakes in the drawing process and things never seem to go so easy-peasey as they first appear.

It does make it a little more troublesome that I use SketchUp in decimal inch formal, to 0.000000" accuracy. This means that when certain dimensions are off a teeny bit it can be a real hair-puller finding out what has caused the discrepancy. This does help me be absolutely rigorous in the drawing technique however. The software has a few quirks in it and crashes once in a while, even though I have the latest version downloaded. Otherwise, I find the mistakes I am so often making present me with lot of additional opportunities to draw the same parts over and over again.

Take the legs which are rotated 45˚ to the plan. While working on developing the views of the short side braces, I found a little discrepancy in a pair of lines that should have connected, but did not, missing by a few thousandths. That may sound irrelevant, and it most respects it IS, but it did mean something was wrong in the drawing, and in some cases SketchUp won't close a face up into a tidy plane if there is a small discrepancy like that - so I needed to dig into it. I tried re-drawing a few times, to no avail, and after puzzling it out a little while longer, I realized that logically the problem had to lie somehow with the legs. I checked the legs, which are supposed to be 2" wide, and found that both were ever so slightly wider at the back - at 2.000439" or something absurd like that. Enough to cause the beak-like cut on the end of the short brace to have edge lines not quite matching up with the plan development. That meant though that the legs needed to be re-drawn. In trying to redraw the legs, SketchUp got all buggy on me and wouldn't cooperate at all, so I had to start a new drawing. At least I was able to cut and paste quite a bit from the previous one into the new, and the legs were drawable on the new sheet.

I have developed the views of all four short side braces- I have figured the technique out enough now that I can draw both the leg and the sections of post which surround it, as in this example:


In the back ground you can see the two slices of post section. These weren't chopped out of the existing posts on the 3D rendering of the entire sawhorse, but developed from the 2D plan, like the brace.

The section of drawing which pertains to the development of the short side braces looks like this:


Actually, this is one side - on the other end of the tréteau plan and elevation views I have a mirror-image drawing of the same development, different only in respect to the generation of lines from one of the legs.

All four braces, now developed on all four sides into 3D from from the 2D, were rotated into the orientation they needed to be in the sawhorse, and 'tried' for fit. This way I could confirm the 2D drawing method was producing an accurate part. Then the 4 pieces were dimensioned and grouped in a separate area of the drawing so I could easily refer to them for the layout on the wood:


Of the four, the one at the bottom right of the picture has a pretty easy lower tenon to cut, as does the upper tenon on the right side, bottom - the shoulder is simply 90˚ across the face. To compensate for that however, there is the tenon and barbe (= "beard") found at the lower end of the top left brace - bleedin' diabolical!:


The barbe on that unit only about 1/4" thick at the root end and tapers to a fare thee well. It will be a fun one.

Today I had more vexations with Sketchup, but in the end managed to complete the drawing of an interior x-brace. Now, one thing about this entire process is that I have no one to teach me, just the text, so I don't always proceed in the originally intended order. Or in a logical order for that matter - "fools rush in where angels fear to tread" as the cliché goes.

In many cases, the drawing proceeds by determining a slope or dimension in one view, transferring it to another view to produce something else, and then often that development allows you to return to where you started with more information, thus allowing things to proceed further. Back and forth you go, dazed and confused for the most part. These interior x-braces are a case in point, and further demonstration of the fact that I am essentially stumbling around in the dark as I try to decipher the book and the methods it shows. And it does show you what you need to know - the trouble is recognizing that when you see it! Not so easy.

In that case of the interior x-braces, which tie the long side braces together, I had already produced them in the 3D drawing so I thought I had them pretty much licked. Ah, nope. I was having all sorts of problems getting the lines to tie up as I thought they ought to, and have pulled the 3D interior brace assembly out of the model and placed in on the plan to see if I could make sense of it. Things still weren't adding up and I was most perplexed. Then I noticed, through performing a bunch of checks, that while I had indeed drawn the interior braces, I had misunderstood the progression of step to develop them and had in fact drawn braces which were parallelogram in cross section. It was funny how I hadn't noticed all this time, even when I laid the assembly down on the drawing. Anyhow, once I saw that issue, I was forced to re-examine a number of assumptions about the text drawing and ba-ding! a light went on for me and I suddenly had a bunch more insight about the drawing. Struggle struggle struggle, and down a hundred wrong paths, but in the end persevering leads to those 'a-ha' moments often enough. Often enough to keep me going in this demented pursuit anyhow.

At last a couple of curious lines on the drawing, which I had long puzzled over and never understood, were now very clear in purpose. Like I said, everything is there to be seen on the drawing, even with all the little mistakes present, and in time it will reveal itself if you keep at it.

Here's the completed development of one of the interior x-braces - all four are identical so I only needed to develop one:


The tenon on the lower end of that puppy looks a bit troublesome, but not so bad as it was looking when the piece was a parallelogram.

All for today- the end of the drawing stage is nigh. Stay tuned. --> Go to part VII

Saturday, November 14, 2009

Tréteau V

The odyssey continues. I've been drawing and drawing and drawing - in between other paid drawing work I am engaged in for a client at the moment - and when I take a break from the drawing, well, I can do some layout on the wood, which is in fact simply more drawing. I'm going batty!

This sawhorse is a fairly complex piece. As of today I have completed the 2D drawing details for, and subsequent layout of, the main top beam, and the four long side braces. I keep thinking about trying to find a way to explain the layout to the readers here, but it is the case I'm afraid that due to the complexity level I would have to spend a LOT of time trying to describe mere isolated aspects of the layout. It seems like a tough thing to explain with clarity unless I write for what might be months. Maybe once I have a better grasp of the subject, after making this piece and letting the material soak into my skull a bit more, I will hopefully find a good way to go about explaining some of the layout stuff.

I'm finding that doing the complete drawing, which I have now done at least 15 times (to one extent or another), takes about 25~30 hours per round. And the layout on the wood hardly proceeds with any great alacrity since one has to be fairly circumspect about it - it's so easy to place the lines in the wrong places. I've done plenty of erasing already - by which I mean scraping, as a card scraper is the means by which I am removing erroneous marks.

The mechanical pencil, my usual choice for layout out on wood, has a lead which is unfortunately of a colour -gray - that blends in with the Canarywood all too easily, so I have switched to a Staedtler 0.35mm black ink marking pen, which does a good job but seems a bit fragile at the tip.

Here's a few pictures of the completed laid out pieces, in no particular order...

The piece to the left shows the inside face where the upper end of the interior x-brace mortise is located, and the piece on the right shows the brace's lower tenon, this one going through a leg which is turned 45˚ to the plan:


Here's a view of the tenon layout at the top end of one of the braces:


The cut-out will definitely be challenging, if not downright diabolical, in a few spots due to the long slopes across faces and tight interior intersections of planes in several spots.

Here's some of the mortises laid out in the upper surface of the beam:


And a view of the mortises emerging at the underside of the beam:


Same view of the underside of the beam, this time of the mortises for the long braces:


And another look at mortises for the legs on the underside of the beam:


The drawing work has been a challenge to figure out, to say the least, partly because of the errors that I find in the original (if it is original and not a copy), and partly because a fair number of development lines are simply omitted from the drawing. To give one example of that, take a look at part of the original drawing which concerns the spot where one of the long braces slopes down to meet a leg:


That doesn't look too bad at all, until one actually goes to work on the development of the brace - in particular the brace which meets a leg turned 45˚ to the plan. Once that scratching is completed, the view is a tad more congested:


It occurred to me that a nice application for this form of sawhorse wold be to make a joiner's workbench. Unlike a table, say, a person doesn't need to pull a chair to sit at a joiner's bench, so the crossing braces wouldn't interfere with anything. Since having a shelf in the lower section of the bench generally just results in, uh, dust collection, it would be fine with just the structural elements. Of course, one could always sling a few drawers in under the top if need be. It would be great to have this sort of structure for a planing bench, as it would be absolutely resistant to back-and-forth loads, much more so than the usual non-splayed trestle-based bench. I'm keeping that in mind for the future, and for now I'm keen to see how this sawhorse turns out. With such a hard wood and all the awkward joints and multiplicity of interconnection between pieces, it seems like it will be a miracle if everything fits just right when assembled. We'll see of course.

Anyway, I'm rolling onward. Next step is to develop the views for the short side braces, then the interior x-braces, and finally the legs. Then lay it all out. I'm guessing, given my schedule at the moment and the somewhat reduced available time I have to devote to this, it will take about a week more to get to the point where the layout is all complete and I can start hacking into the wood.

Thanks for visiting today. --> Go to part VI

Tuesday, November 10, 2009

Tréteau IV

Well the last few days have been a little chaotic for me. First of all I came down with a cold which slowed things down a bit. Then, while getting towards the final stages of some drawing work I am doing as part of a consultation, SketchUp started overwhelming my computer and it repeatedly crashed. I would restart and then find that some data had been lost, even if it had been previously saved, and this resulted in more than a little hair-pulling and stress. It gets a little old when you find yourself drawing the same thing for the fourth time and not sure if it will be lost again.

So, I went out and got a new computer - a new Mac Mini to replace my old Mac Mini. The processor chip is nearly twice as fast and it has about 8 times the memory of my older one - and the price had remained unchanged at $799. No surprise there. What was surprising, after I had transferred my data over and got the new machine up and running, was to try and hook up the the internet. You see, I live in one of those pockets of Massachusetts, akin to sub-Saharan Africa or perhaps isolated Pacific atolls, where there is no available high speed internet, no cable, no wireless reception, nada. It's use a 56k modem or nothing. Actually, maybe sub-Saharan Africa does have high speed now.

I went to plug the phone jack into the back of my new computer and I discovered that there was no phone jack(!). I guess dial-up is so hopelessly old fashioned now that computer makers don't even bother to install such hardware. Along with the lack of a phone jack, I learned that my computer doesn't even have an internal phone modem, and, after talking with a guy at the computer store, learn that OSX 'Snow Leopard' does not actually 'support' a dial up modem function. It was looking like a total disaster for a while, with two computers and a snarl of wires on my desk, with the monitor having to be switched manually back and forth between computer drives, $800 in the hole with a computer I couldn't get on-line with....

Anyhow, I have since learned that the computer shop was not entirely accurate in their comment - while the new operating system does not 'support' a phone modem, if you plug in a Mac USB modem, it can actually read it just fine and connect. Of course, Mac has stopped making such outdated devices, and no store around here has one in stock, however I was able to locate one online and it is on the way to me now. My neighbor is letting me borrow his for the time being.

It's funny to think about the pace of technological change sometimes, as it is an accelerating phenomena, ala Moore's Law. My old Mac Mini went 4 years before the software started to overwhelm it's chip and memory capacity. My new one I might expect to go 2~3 years (?) before reaching the same point. That pace of change is accelerating, so I am left to wonder when the point will come where I buy a new computer and find it is out of date and unable to keep up within days of my purchase. It's a strange sci-fi becomes reality sort of world.

I'm reading a book right now by a Princeton Professor name Wolin, called "Democracy Incorporated" in which he contends, among other arguments, that the pace of technological change, a feature very much associated with the society I live in, is so rapid that it doesn't allow the previous changes to 'sink in' or be fully adopted by society. He included the 'social technology' of participatory democracy, the phenomenon of the democratically-engaged citizen, in other words, in that list of changes that never really took because they were supplanted, and continue to be supplanted, by subsequent developments. What we have right here right now is what Wolin calls inverted totalitarianism, in which the state exists to serve the needs of business and 'democracy' as such is managed like a business or other complex system- instead of an engaged citizenry, we have a passive consumer society that confuses an occasional trip to the ballot box (uh, for those that bother to make the trip) with 'democracy'. And that disengaged passivity on the part of the citizenry is exactly what the power structure would prefer for the masses - entertained, distracted, disengaged, feeling powerless yet able to scrabble amongst themselves for minor possessions. Anyhow, that's another topic, but the read is quite intriguing so far and I recommend the work, if you can stand a little bad news.

As far as the tréteau goes, I have managed to make some good progress despite the past few days. The top beam is all laid out and I have laid out the tenons and shoulders on the tops of the long braces. Through my ongoing study, I am working the 2D drawing to develop the views of the various parts and determine the required cut angles and lengths. These measurements i can then check against the 3D drawing to confirm. Through this process I have had a couple of minor breakthroughs in understanding the drawing method in the book, and have found yet more lines in the book that are mis-drawn. Again, I am surprised to have found so many mistakes in the drawing, and am left to wonder how it has come about. My latest theory is that either the drawings are copied by someone who was not Mazerolle, or perhaps the drawings are partially reconstructed from a surviving old text, where the lines had become faded and someone in recent times attempted to re-draw, making several mistakes along the way. Whatever the case, it keeps me on my toes, and I would not be surprised to find more errors in the original text in the next few days.

I have completed the drawing work on the tenons for the interior x-braces, and wanted to share some pictures. Here's a view of one x-brace, with a long side brace pair removed from the scene:


From low down at the post corner, here's another view:


I also found a pair of base lines on my drawing that were out by, oh, a few ten-thousandths from where they should have been, and this was causing weird issues with the layout of the tenons in the top beam. So I corrected the location of those lines, then redrew all the tenons and mortises for what seemed like the umpteenth time, and here is the result of that:


The top beam is ready for cut out as is now, though I am debating whether to partially or fully house the legs into the beam, and that decision will affect the layout. The housings make sense usually, as it makes for a stronger connection than the tenon alone, however with so many interconnected and cross-braced parts in this sawhorse, I wonder if it is a moot consideration.

I have to yet to complete the developed views for the various tenons and mortises where the long braces meet the lower legs, and then I can complete the layout on the long braces and move to the leg layout. After that I will deal with the short side braces, and lastly the interior x-braces, the only group of parts on this project which will all be laid out identically. The next few days will be drawing, calculating, checking, and then laying out - and then re-checking. There are 4 long braces, and only 2 of them are identical to one another - the other pair are each unique. It is a struggle to keep the parts distinct in my mind and make sure that they are laid out in their own unique way without confusing things between one and another. I've already laid out the long brace top tenons three times due to errors and mis-assumptions. I need to check and re-check that I have things right. Putting the lines in the right places remains the penultimate carpentry challenge.

--> Go to part V

Wednesday, November 4, 2009

Tréteau III

Some progress realized today, both in the real and virtual worlds. I took the material down to the street and worked with a guy to joint and plane all the material, managing to get all the pieces to about 0.015" oversize:


I'll be working on putting the lines into place next, aiming to lay out all the sticks before proceeding to cut out.

So I returned to the drawing to work on getting all the tenons sorted out, which helped me learn a few more things about how the drawing method works, and I also discovered a goof up on my part with the interior x-braces which connect the long side braces together - I had them fitting fine but of a smaller size than they should have been. It had been a case of connecting to the wrong line in the first place and then managing to put all my marks on the wrong line. I've sorted out now, and that has made the x-brace section a fair bit taller, by 0.25" or so.

I thought I post up a few pictures of the varied tenon arrangements on this piece. It's possible to squeeze every last little bit of space out of a given tenon junction - note how the protruding tenon on this leg slips in under the short-side x-brace barbe:


The tenons themselves diminish in an unusual manner, by simply tapering:


The arrangment is different in every case - here's the opposite leg to the one above:


And an interior view with the leg out of the way:


The short side x-braces will have tenons as well - I haven't gotten to that part yet. They will penetrate about halfway into the leg at each end, not run through. The x-braces that run between the long side braces will however through tenon and will also taper.

The tapering is presumably to make it possible to assemble, given the way that tapered post structures have to go together incrementally, a little bit here, a little bit there.

At the top of the sawhorse, the legs tenons are all quite varied too - here's one end:


On the opposite end of the beam you can see where the two legs slightly interfere with one another:


I'll be trimming the corner off the left hand leg.

The mortising will not be so easy in some spots, that's for certain. The right hand side leg in the picture above will be the easiest case, since that leg is rotated to the short axis and thus the mortise will be square (on horizontal alignment). It's opposite number requires a parallelogram-shaped mortise, and the other two have 5-sided profiles.

I've got another few hours of drawing ahead of me yet before I can start on the layout on the material.

All for today. Thanks for dropping by. Go to part IV

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

Sunday, November 1, 2009

Tréteau

I decided to start a new thread for the Mazerolle sawhorse build instead of continuing on with the "French Connection" series, since there are a lot of other French 19th century joined structures I wish to study and build and can take up that series later with those other pieces. The tréteau is but one example of French classic carpentry, and I thought it best that it have its own thread. Welcome to the puzzle.

Choosing the wood turned out to be easier than I thought, and I didn't even need to make a trip down the road to the local hardwood supplier. I had 5 planks in my little storage closet that were of adequate dimension to produce all the wood I would need for this horse. I hoped to get it all out of one plank, but I needed a little 24" bit out of a second plank.

The work will be done, once the stock is ready, almost entirely with ink line, knife, chisel, saw and plane, due to the nature of the odd-shaped joints involved. However I'm sure my electric drill, and possibly the router will still prove useful from time to time, and for the initial rough cut-out on the 8/4 stock, my circular saw was brought into action:


The saw is a 190mm 'finishing saw' made by Hitachi, available only in Japan. It is light in weight, has a 20 mm arbor, electronic motor control, cast aluminum base plate, and even a laser, which is handy once in a while. Too bad it couldn't actually cut with the laser - I guess that's a few years away! It's a very quiet saw and I could get away without ear pro if it were only a few cuts, - which it wasn't. It's a real pleasure to use a nice circular saw like the Hitachi.

So the wood. Let me describe it - the Latin name for it means 'many lobes on leaves' and it is a member of the pea family of plants, Leguminosae. It occurs in scattered fashion, not in stands, and is native to Panama to Ecuador and southern Brazil. This tree's wood that I obtained is FSC certified and the species is not threatened. The tree grows to a height of 100' or so with a trunk diameter of up to a maximum of about 50". It produces yellow or purplish flowers in season. Here's a young one:


The flowers, after pollination form large seed pods, which resemble a cross between a Chestnut burr and a Maple seed, on a rather large scale:


The average specific gravity of the wood ranges from 0.61 to 0.69, about 15~20% denser than Mahogany. This will not be the world's lightest sawhorse, but it will be pretty damn tough. The wood of this species is really stable, both in drying and in working, with a near perfect T/R shrinkage ratio of 2.3/1.

After the slicing and dicing with the saw, I discovered that the dust of this species is really not pleasant to breathe at all - good thing I did the work outdoors with a mild breeze at my back, and of course, will be employing no sanding in the actual working of the material. Here's the tidy pile of rough stock after the saw was put down:


One of the reasons I decided to use this species of wood was because I already had it on hand, which was convenient of course, but it also turns out to be, unlike most light-colored wood species, highly rot-resistant. It is also unappealing to termites and other insects. It has a grain structure that makes it near-impossible to impregnate with preservatives, which means it will also tend to not absorb moisture from the ground or air.

In it's native locales, this wood is used for heavy construction including railway ties, as well as flooring, and also ship components like planking, keel, decking and trim. I bought the wood though for its reputation of easy workability with hand tools and intend to turn some of my pile into furniture or cabinetry one day. I'm looking forward to pulling some shavings off of this stuff.

This wood is really stunning, I must say, even at the rough-cut stage:


Believe me, the above picture does no justice whatsoever to the vivid streaks of color in this species. Yellow, purple, and red steaks - so beautiful!

I will be using my palatial workbench - the irregular splay sawhorse that served the same duty for the lantern build (the "First Light" thread), as the basis of operations. Here, I am using the horse to stack the wood, letting it rest overnight:


Now, my next move is to take the pile of sticks to be jointed and planed to near-dimension at the window and door place down the street (maybe I can convince them to let me work the jointer and planer). That will save me a lot of labor and time for a mere $30, and give me a nice straight and square starting place for the layout. This sawhorse project is all about the layout after all.

So, has the reader guessed which wood I'm using here? Well, I'm not going to hold you in suspense in case you haven't twigged on (no pun intended): I'm using Canarywood, centrolobium robustum. This is the first time I've worked the stuff, so it will be a learning experience in many ways. Hopefully time will prove I made a good choice.

Go to part II.