Wood is like a box of chocolates…
Insider Secrets for Crafting Excellence
When it comes to woodworking, selecting the right wood is more than just picking maple for a table. It's like choosing the perfect avocado—you need to feel it, know its quirks, and hope it doesn't disappoint when you cut into it.
Wood is like a box of chocolates—no, scratch that. It's more like a Pandora's box of surprises. You see, when a tree meets its maker (the sawmill), it undergoes a transformation that would make even a caterpillar jealous. From moisture content to shrinkage and swelling, wood is a living, breathing entity that refuses to be tamed by mere mortals like us.
Let's talk about moisture content…
Because who doesn't love a little hydration drama? High moisture content means your board will shrink faster than a wool sweater in a dryer, potentially leading to unsightly gaps in your project's edges and seams
On the flip side, low moisture content might have your board puffing up like a marshmallow over a campfire. It's akin to playing a suspenseful game of "will it fit?" with your woodworking projects, but the stakes are higher (and the tears are real) because the wood may swell or buckle in response to high humidity. Ever experienced a door in your house that refuses to properly close during the humid summer months? Or perhaps your front door shows a sliver of light along the edges in winter, but not during the summer?
How much shrinkage or growth to plan for is always a topic of debate within the woodworking community. In the past it has been up to the woodworker’s best judgment when deciding these tolerances. However, now in the information age we can turn to the internet for answers and we have actual wood shrinkage calculator websites at our fingertips.
You mean… shrinkage (and swelling)
Shrinkage and swelling are the most common and visible signs of wood movement, often manifesting as changes in dimensions that can affect the fit and functionality of a project. These movements occur primarily along three axes: tangential, radial, and longitudinal.
Tangential shrinkage, which occurs perpendicular to the grain and parallel to the growth rings, is typically the most significant factor influencing dimensional changes in flat-sawn boards. The extent of tangential shrinkage can vary widely depending on the species of wood, with some, such as teak, exhibiting minimal shrinkage, while others, like certain oak species, experiencing more pronounced changes.
Radial shrinkage, which occurs horizontally from the center of the tree to the bark, is generally less pronounced than tangential shrinkage but can still contribute to overall dimensional changes in a board. Wood that has been riven or quarter-sawn from the log will typically exhibit less radial shrinkage compared to flat-sawn boards.
Longitudinal shrinkage, which occurs along the length of a board, is minimal and is rarely a significant factor in wood movement. However, it is important to consider when designing projects that require precise dimensions or joinery.
While wood movement is an inherent characteristic of the material, there are several strategies and techniques that I as an experienced woodworker employ to minimize its impact on my projects. Proper milling and seasoning of lumber, for example, can help stabilize wood and reduce the risk of excessive shrinkage or swelling.
Additionally, choosing the appropriate joinery method(s) and allowing for adequate expansion and contraction of wood components can help accommodate changes in dimensions and prevent structural issues such as splitting or warping. Techniques such as breadboard ends and floating panels are commonly used to allow for wood movement while maintaining the integrity of a project's design
Uneven shrinkage and swelling
Despite our best efforts to mitigate wood movement, some degree of warping, twisting, or checking is inevitable in woodworking. These imperfections, while frustrating at times, are a natural consequence of working with wood and can add character and authenticity to a project.
Warping, which encompasses various forms such as cupping, twisting, bowing, and crooking, occurs as a result of uneven drying and tension within the wood. While some degree of warp is common in most boards, excessive warping can be indicative of improper drying or milling practices.
Cupping is a form of warp that has changed the flatness of a board across the grain and is a result of Tangential shrinkage and is directly related to how the board was cut from the timber and moisture content.
Twisting, this is when a board is not flat across the corners and when laid on a flat surface only 2 of the 4 corners touch the surface.
Bowing, this is when a board is not flat lengthwise.
Crooking is when the board is not straight along its edge.
Distortions of wood due to Shrinkage and Swelling
Selecting wood is a art and science. It takes woodworkers years to learn how to select the right wood for a project.
The cause of twist, bow and crook can be directly related to uneven drying in a board due to “Reaction Wood” often associated with an unusual spiral grain, an unusual growing environment or juvenile wood. A slight twist, bow, or crook is common in most boards, however some wood is more susceptible to violent changes when not dried properly.
Warping issues in general result from tension and compression within the tree as the tree grows and becomes evident when milled into boards. If you look at some trees as they are growing you may see some evidence of this. Where a tree grows in a forest has a lot to do with these characteristics in a board. If a tree is growing under another larger tree it may be struggling to get sunlight, so it grows in an odd direction. Maybe that same tree was affected by the larger tree dying, giving it more sunlight so now it can grow in a new direction creating a twist in the tree. These possibilities are endless, and it is up to the woodworker to manage these issues.
Checking, this happens most often as a result of a board being dried too quickly, and as a result the board or log will develop cracks close to the ends. Another cause could also be that the board was cut from a part of the tree that was weakened by stress like persistant winds. Checking from wind stress is commonly found in the heartwood of hardwood, because of its fibrous support cell structure, and can happen almost anywhere in a softwood tree because the cell structure is more uniform. This type of wind stress checking is more pronounced when lumber is dried under the best of conditions. While checking can detract from the aesthetic appeal of a project, it can also be embraced as a unique feature that tells the story of the wood's journey from tree to timber.
In the end there is rarely a perfect board, there will always be some type of issue to address. It is up to the woodworker to take all of these issues into account when making a selection. Often the decision is easy, just don’t buy a board with a big problem. However the grain of a board might force you to overlook warping and checking issues simply because it is beautiful. The fact that you will have to do extra work might become secondary to the issues because you know that your end product will be much more desirable to the beholder or potential buyer.