Bent, Not Broken: The Natural Process of Shaping Fantastic Wooden Forms

Masonic Amphitheatre, Design/Build Lab at Virginia Tech. Image © Jeff Goldberg - ESTO

Even as technology advances—leaving many of the old ways of building obsolete—certain traditional crafts and building techniques continue to captivate our imaginations with their simple ingenuity and unimpeachable effectiveness. Although used for millennia, the process of temporarily turning rigid members of wood into pliable, twistable, bendable noodles of lumber remains a favorite woodworker’s trick, capable of producing whimsical transformations and otherworldly forms from the most natural of materials.

Thonet Rocking Chair. Image © Dominik Matus / Wikimedia Commons / CC-BY-SA-3.0

Historically, steam bending has been most often used by wooden boat builders for shaping curved rib-like frames, by furniture builders for crafting swooping crest rails on chairs, and by luthiers for creating the shapely sides of hollow string instruments like guitars, cellos, and violins. The manageable scale of these crafts allows for the pieces to be prepared in homemade airtight steam boxes, often attached to a steam generator (basically a large tea kettle with a hose fitting) or a homemade boiler. Builders follow a basic rule of thumb: the stock needs an hour in the steam box for each inch of its thickness (depending on species).

A typical woodworker's steam box. Image © Steven Vacher / Flickr / CC-BY-SA-3.0

Using this method even substantial boards can be bent and twisted into exquisite compound curves, and thinner pieces become so pliable that they can be tied in knots without cracking or splitting.

So, how does it work? When exposed to the heat and moisture of a steam box, the lignan that binds a piece of wood together starts to soften, allowing the cellulose fibers that compose the major structure of wood to twist and bend into new shapes. At this point, the steamed stock can be molded into a vast array of shapes and left to return to room temperature and ambient humidity, allowing it to return to its original stiffness as the lignan cools while maintaining the twisted or bent form desired.

TRILUX Pavilion, Future Cities Lab. Image © Peter Prato

While other techniques of bending wood allow similar shaping capabilities—like laminating together thin, bendable sheets or pieces with strong glue, or simply cutting larger stock into curved forms by saw—none preserve the strength and structure of the wood’s fiber like steam bending.

Saw-Mill Shelter, Architectural Association School of Architecture. Image Courtesy of Rolando Madrigal Torres

The practicalities of constructing and operating a steam box usually limit the potential size of steam bent wood applications, particularly in architecture, but daring designers have found a number of innovative ways to incorporate bent wood into schemes at various scales, from the intricate to the ambitious.