The Exploitation of Wood

When designing furniture, the outward form of the piece is important, but equally important is how I exploit the wood to do things that are surprising or occasionally alarming.

I use the word “exploit” deliberately. Though “exploitation” has a fairly negative meaning in today’s lexicon, it is the correct term. In many ways I seek to take full advantage of the wood, perhaps even treat it unfairly to get what I want.

What do I want? Well, in this column I’m going to discuss how I fool the wood into acting like timber from the 18th century (which we can’t get anymore), or to become impossibly strong, even when shaved down to extremely thin cross sections.

Exploiting the wood (or any material) requires an intimacy with the stuff that goes beyond most textbooks. And as a designer, I can never know too much about my materials. After working with wood for decades I still think I have a lot to learn. And with steel – the other material I work with a lot in toolmaking – I still consider myself a kindergartner.

My graduate work in wood began with an 18th-century French treatise (aptly) titled “De l’exploitation des bois” by M. Duhamel du Monceau (1700-1781). His 1764 book was perhaps the first Western book exclusively about wood as a material.

I’ve translated several sections of it during the last decade, but even if you can’t read French, the drawings are enough to make your brain churn. In this book, Duhamel explores how wood can be manipulated to make objects such as shoes, frames for saddles or basketry.

M. Duhamel was keen on looking for the shapes he needed in the living forest.

Most shocking, for me at least, is the section where Duhamel demonstrates how to use the natural shape of the living tree to create a curved (and crazy strong) component for a wooden warship, for example. Since then I’ve learned of ancient cultures that actually trained trees in the forest to grow into particular shapes that they required for a chair, a horse collar or a plate rack. Exploitation indeed – poor trees thought they could avoid being harvested by growing into an undesirable shape. Sorry trees.?

Axel Erlandson was one of the 20th century’s great exploiters of trees and grew them to suit his sculptural needs.

Three Exploited Trees

Let’s dive into some examples that show why you should become intimate with wood (or steel or carbon fiber or…). All three examples begin with a typical design problem. And the solution requires science, trickery and perhaps a little cruelty.

The first problem goes back to 2005 when I was researching ancient French workbenches. After translating another 18th-century French book (A.J. Roubo’s “l’Art du menuisier” or “The Art of the Woodworker”), I wanted to build a workbench that had the same characteristics as the benches discussed in Roubo’s work.

The workbench shown here is a classic design. The problem is the timber required to build it isn’t available anymore. What to do? Get out the scientific charts.

“The top is made of a plank or table of 5–6 thumbs (inches) thickness by 20–22 thumbs in width. For its length, that varies from 6 to 12 feet, but the normal length is 9 feet. This bench is of elm or beech wood but more commonly the latter, which is very solid and of a tighter/denser grain than the other.”

— With All the Precision Possible” (Lost Art Press), a translation of sections of A.J. Roubo

So, you need a plank of elm or beech that is about 6″ thick, 20″ wide and 9′ long. If you go to the lumberyard and ask for this, you will be laughed at. Modern sawmills rarely cut stock thicker than 3″ or 4″ thick. Why? It’s mostly economics. Almost all sawmills dry their wood in a heated kiln, and thick material is difficult to dry without the boards self-destructing. Before drying kilns became common in the late 19th century, wood was air-dried, a process that might take years instead of days.

Bottom line: Most modern woodworkers won’t be able to easily find a dry plank of wood in those dimensions without immense difficulty or cost. Instead of giving up, I tried to get inside Roubo’s head. Was there another way to build this bench without first building a time machine?

Why would Roubo insist on wood that was 5″ or 6″ thick? (Modern workbenches are less than 3″ thick.) My guess was that it was for two reasons: the mass and the stiffness that thick material provides.

Mass is desirable in a workbench – it prevents the bench from skittering around as you work on it. Stiffness is also important. If the top flexes (even the tiniest bit) handplaning a board becomes almost impossible.

Why would Roubo specify elm or beech as the woods for a bench? Neither is a fine furniture wood by traditional standards. Beech is the red oak of the European continent – it is plentiful, cheap and is used for lots of utilitarian objects. Elm is used in some furniture, though it is difficult to work. That was a clue – neither wood is particularly valuable to the fine furniture maker.

Both woods are quite heavy and dense (they are similar in weight to North America’s hard maple). That was the second clue. Also, neither species has a lot of open pores. This is a minor point, but open-pored woods such as oak and ash could collect dust and metal filings. Closed-pore woods offer a much smoother surface.

My first Roubo workbench, built using Southern yellow pine, has the same mechanical properties as the bench from the 1700s thanks to a knowledge of wood’s properties.

So, I decided to look for a wood that was heavy (about half the weight of water, in terms of specific gravity), inexpensive, widely available, stiff, not particularly desirable as a furniture wood and had closed pores. While there were several contenders, the yellow pines – longleaf pine, loblolly pine and shortleaf pine – turned out to be dead ringers for a Roubo-style workbench.

These particular species of softwoods happen to be a perfect workbench wood. They are heavy, cheap, stiff, common and have no real pores. The only problem is you can’t find them in 6″-thick slabs. My solution? Buy 2 x12s, rip them in half and glue them face-to-face, effectively creating a 6″-thick slab.

This worked brilliantly. With yellow pine – readily available from any home center – I could build a 300 lb. workbench for about $250. Plus, it had all the mechanical characteristics of an 18th-century bench. Instead of having to wait a decade for a slab to dry out (or pay through the wazoo for someone to do it for me), I exploited the wood’s mechanical properties (thanks to the “Wood Handbook” from the U.S. Forest Products Laboratory) to get what I wanted – quick and cheap, too.

Laminating the top using a species that mimicked ancient beech created a benchtop I couldn’t buy for love or money.

The only thing it lacked was that it didn’t look like an 18th-century bench because of all the glue lines. With a workbench, appearance isn’t terribly important, but with a dining table, it’s critical. And that leads us to our next puzzle: really wide boards.

Amazingly Wide Boards

One of the big differences between modern and ancient work is the width of the boards used in the show surfaces, such as the top of a dining table. Thanks to the bounty of the forests in the New World, furniture makers in the 17th through the 19th centuries were able to use boards that were 30″ wide – or wider. That meant that a tabletop could be a single wide board, which is visually stunning.

Modern tables – especially mass-market ones – have tabletops made up from narrow boards that are glued together edge-to-edge. Sometimes the individual boards are only 2″ or 3″ wide. Unless you paint a tabletop such as this – or stain it into dark oblivion – it looks like crap.

Today if you want a single wide board for a top, you have to pay for it. Really wide boards can cost three to five times as much as narrow boards of the same species – if you can even find them for sale. This problem has vexed me for a long time. My solution relied on visual trickery and a firm knowledge of the structure of the wood.

In essence, the trick is to glue up several boards to make a wide top but to camouflage the joints so they are invisible. Some of the camouflage tricks were obvious:

Use boards cut from the same tree so their color and texture are consistent.

Pay attention to the annular rings. Boards have two broad faces. One face usually faced the bark of the tree (called the “bark face”) while the other face usually faced the center of the tree (called the “heart face”). These surfaces reflect light differently. (It has to do with the way light bounces off the interior or exterior surfaces of the wood’s cells.) Bottom line, all the boards for the show surface of the tabletop should be either heart-face boards or bark-face boards. Not a mix.

Most wide boards have grain lines that look like arrows running down the center (what woodworkers call “cathedral grain”) with straight grain lines running down the edges of the board. The trick to making a board look wider is to glue on boards that have similar grain patterns.

The third trick is the trickiest. Lots of woodworkers take a wide board and position it in the middle of the top. Then they glue on boards that feature only straight grain lines to the center board. This fools the eye into thinking the top is one wide board.

But it really doesn’t.

What most woodworkers forget is that trees trunks are cone shaped. They taper toward the top of the tree, so the straight grain lines taper as well. So, to really fool the eye, all the boards in the tabletop have to taper so that the grain lines are parallel and continuous.

Here’s how I fool the wood into looking like a massive single board (something you can’t easily buy). Follow the grain lines closely and you can fool most people.

So instead of gluing up a bunch of rectangles edge-to-edge, you need to glue up a bunch of odd and tapering polygons. Then, after the polygons are glued up, you cut the resulting mass into a perfect rectangular tabletop. It’s more work. And there’s more waste. But the result is worth $1,000 (or $10,000, depending on the checkbook of the customer).

The exploitation? Instead of allowing a tree to live to be 150 years old before being harvested to be a one-board tabletop, I can get what I want by using a 40-year-old tree instead. And I don’t have to pay an exorbitant price for the 150-year-old tree.

Incredibly Strong Spindles

Gluing up a top as described above is designed to fool the eye of the customer. Sometimes you need to fool the wood itself to get the job done.

One of the reasons old chairs survive centuries is the wood. On many high-quality old chairs, the wood was cleaved – or rived – from the tree instead of being sawn. This cleaving process ensures that the wood fibers in the stick are continuous from one end of the stick to the other. These continuous fibers make the stick incredibly difficult to snap, even when crazy thin.

The spindles in this chair taper to almost 1/4″. That’s alarmingly thin and these would snap easily if I hadn’t sawn them in a special way.

Sawn stock, on the other hand, is traditionally weaker because it doesn’t have these continuous fibers. So, spindles, legs and other sawn components fracture with ease, especially when thin.

Splitting (or cleaving) your wood ensures the fibers run from end to end. But not all species split easily. And only certain trees grew straight enough for this operation.

Cleaving your stock has disadvantages. You need to get your wood from the forest (or from a tree service). It’s still wet when you begin working it. And you have to dry it yourself, which can take patience.

When I started making chairs for money my goal was to find wood that had the same continuous fibers as cleaved stock, but to do it with sawn wood that I could buy at my city’s local lumberyard.

Take a close look at the grain lines on the edges of these boards. In the top one the slanted grain would make a weak spindle (yet many factory chairs are made from this stuff). On the board below the grain is arrow straight, which makes it a candidate for a chair spindle.

The trick turned out to be to fool my sawn lumber into behaving like it was cleaved. I did this by opening my eyes to how I bought wood at the lumberyard. When most people buy wood at the yard they look at the wide faces of the boards for knots and beautiful figure. Instead, I also examine the edges of the boards for grain lines that run straight all the way up and down the board. Those straight grain lines indicate that the fibers are nearly continuous through the thickness of the board.

Here you can see how I marked out a spindle in a board. By following the grain on the edge and the face of the board, I can create an incredibly strong piece of wood.

With the fibers continuous through the thickness, I can then saw out my chair parts from the wide face of the board by marking out my parts so they follow the grain there. And bingo, I have old-school parts that are incredibly strong. Like cleaved material but without all the work.

50 Shades of Green

Now if you’re smart, you probably aren’t buying my contention that I’m “exploiting” the poor defenseless wood. And you’d be right. While you could look at these tricks as exploitation, I prefer to look at them as ways to conserve a precious raw material via a deep understanding of the wood’s mechanical properties.

So, to build a workbench, I substitute quickly grown plantation softwood for massive old-growth timbers. To make a wide tabletop, I avoid using the biggest trees, which are more suitable for veneer when they reach the end of their lives. And to make strong chair parts, I use materials that are easily obtained locally instead of traveling deep into the forest and making an environmental mess of things there.

Truthfully, “exploitation” sounds a little more Fellini-esque and naughty. A lot less like an environmental film strip from Mr. Peel’s 8th-grade science class. And when you’re a boring old woodworker who talks to his materials, you take all the excitement you can get.

Legerdemain aside, the design lesson stands: A deep understanding of your materials gives you superpowers over designers who don’t.

Christopher Schwarz is the editor at Lost Art Press and one of the founders of Crucible Tool. He works from a restored 1896 German barroom in Covington, Ky. You can see his furniture at christophermschwarz.com.


Source: core77

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