This is the first post of an ongoing series about wood. Understanding its nature, the way it moves and changes, and the implications for designers and builders. Check back every Wednesday for the next installment.
Here's a dangerous assumption we might make about wood: That is once it's cut it remains, more or less, the same. But this is not the case. Even after being cut it moves; it expands, contracts and warps. And this movement often results in dramatic alterations to (or completely ruins) the design of furniture or environments. Understanding the nature of wood is the first step to avoiding surprises, and it is crucial knowledge for a furniture designer to amass. Changes in humidity alone can remove or add as much as a quarter-inch from a board's width. Think about what that might do to your carefully-placed joints on either side of, say, a tabletop you'd designed, that was comprised of four boards glued together along their edges: if each board grew 1/4” in length during a humid summer, you'd have an inch overall of added width—and joint failure where the tabletop connected to the skirt or legs.
So to unpack wood, I'll start a few steps before the lumber finds its way into your shop. What goes into a sawmill is logs, and what comes out of it is boards. But turning the former into the latter is a more detailed process than one would think. Initially it's a geometry problem: We have one log and we want to cut it in such a way as to yield the most useable boards. Over the years, sawyers have devised multiple ways to cut boards:
In this series I will describe each cut—its advantages and disadvantages—and its best applications.Let's start with plainsawn, also referred to as flatsawn or "through-and-through." Looking at the illustration above we see that plainsawn yields the most useable wood with the least waste. The boards are cut in parallel, one right after another, right through the pith of the log. Plainsawn is simple, very fast, and the most cost-efficient. And that's why this is the type of cut found in most mills. And the cut can be used for the most species of tree. In fact these days where serious custom milled wood is becoming more and more rare, plainsawn is typically the cut that people use for well, nearly everything. It is estimated that well over 90% of all logs cut into boards are cut plainsawn.
"Quartersawn is used only in situations where the grain, or look of the wood, is very important or the quality of wood is very important," says Josh Vogel, a wood artist and owner of Black Creek Mercantile and Trading in Kingston, NY. "These days everything else is pretty much plainsawn."
Plainsawn yields distinctive patterns on the face of the board. Because it is cut parallel through the log it results in a face with ripples, large graphic ovals and U-shaped patterns, also referred to as "the cathedral effect." You can see the long ring patterns, that lie almost parallel to the face of the board, here:
While the dimensions of the "cathedral" will vary depending on where in the log the board was cut--think of the variety of places where the tree's rings will intersect the cut line--you can look for it to quickly identify if a board has been plainsawn. Here are some examples of boards where the cathedral does not always come to a perfect point, but that you should still be able to identify as plainsawn due to the characteristic ripples:
It's worth noting that most may refer to this as the "grain" of wood when actually the correct term is "figure." So if you want to display your new expertise, say this instead: "The figure of that wood table is really beautiful." By the way, the word "grain," when used alone, technically refers to the different kinds of cells within a tree that form the characteristic growth rings.
Of course, plainsawn wood is only attractive depending on what you are building. It might be great for a long dining table but not necessarily for kitchen cabinets. For a smoother, more refined look consider either quartersawn or riftsawn boards (more on those cuts in future posts.)
The big drawback in using plainsawn boards is how much they change due to drying, aging and changes in humidity. Take a look at this shot:
This angle is known as "end grain" of the board. As a board ages and dries the tension of the grain can cause the boards to twist, cup and bow. While every type of cut yields boards that will absorb and release moisture, plainsawn boards are the most likely of all to suffer distortion during that ongoing process. In fact, the longer the length of tree ring that you see in the end grain the more likely the board will cup or bow.
Some final tips:
If you are going to use plainsawn wood, have it kiln-dried so that any movement and shrinkage is minimized. Also, keep in mind the final destination for the wood. If you are building a piece in hot, dry Phoenix and shipping it to rainy, humid Seattle you may want to consider a more stable cut like quartersawn, which we'll discuss in a future post.
The way you join the wood can also help accommodate movement. We will discuss some options for joinery in future posts.
Also from a design perspective, if you are having the logs sawn at a mill, ask the lumber sawyer to stack the boards (for drying) in the same order as they were cut. This way it's much easier to match up the grain, figure and color of the boards.