Wood Moves: Seasonal Expansion & Warping

WoodWise

(Welcome Johnny! — Johnny Williams is our new columnist for WoodWise, a weekly post exploring furniture construction and woodworking.)

Wood is never quite willing to stray from its roots. Each time a furniture maker transforms a tree into a table, they must defy the rules of nature, always bound by the simple dynamic that wood moves. Heirloom quality pieces made from solid wood take this movement into account, expanding and contracting with the grace of a sleeping lover (ed. note: you've been spending too much time in the woodshop!). So be careful furnishing your bedroom with high quality pieces — you might wake up spooning the bedside table.

As a woodworking student, I’ve been staggered by how much wood movement impacts design and construction. Expansion caused by seasonal fluctuations in humidity causes constant shifts in size and shape. In the northeast, furniture reaches its peak expansion following the dog days of summer humidity. You may have noticed your drawers are a bit snugger these days, and I'm not talking about all those Shake Shack burgers you've been eating. In solid slab construction, such seasonal movement is inevitable, and always occurs across the grain of a board.

A tree just wants to be a tree; once milled, it will always try to strike its original pose. Wood warps in one or more of the five following ways:

Pin it button big

Cup: to warp along the width of a board
Bow: to warp along the length of a board
Twist: to warp in opposite direction at either end
Crook: to warp along the edge of the board
Check: to split along the length of the board (often due to improper drying)

Furniture makers employ a bevy of techniques to control wood movement. The most basic is to orient their various parts such that the entire piece expands and contracts in the same directions. The solid slab entry table that I’m currently building, for instance, was designed to breathe downward and upward, and not forward and backward.

Pin it button big

Larger slabs of wood move more, so I utilized a frame and panel technique to break up the tension. Panels sit loosely, or float, in grooves inside the frame, free to expand seasonally across the grain but trapped from warp.

For many modern furniture makers, wood movement has become a non-issue. Using fiberboard and plywood has allowed for a whole new era of visionary form and function largely free of motion. But in my very humble opinion, nothing compares to the organic beauty of solid, moving wood. Now enough with all the innuendo, I have some spooning to do.

(Images: 1 Johnny Williams, 2 Wood Magazine, 3 Johnny Williams)

Johnny is currently blogging his experience as a student at Maine's Center for Furniture Craftsmanship. You can keep track of his projects on his blog, Woodlearner.