With all that precise 90-degree joinery, furniture makers can be pretty square. But when life's boring corners get us down, we make curves. Steam bending is a favored technique for such shaping, ideal in building everything from canoes to Windsor chairs.
Before it gets bent, the wood is placed in a steam box to loosen up. The heat and moisture soften the wood's celluloses (polymers that comprise its cell wall structure), which yields a surprising flexibility. The steamer is an uncomplicated contraption consisting of four main parts. First, there's the box itself, most commonly built with plywood, PVC or metal piping. To generate steam, two components are necessary: a small water boiler and a heat source such as a hot plate or gas burner. The boiler generates steam like a kettle — once joined to the box with a length of hose, it fills the box with steam. Of course, you'll need a hole for some steam to escape, unless you want to turn your wood into scraps...or shrapnel more likely. Despite such risks, building your own steamer is a feasible DIY project. The Bay Area Woodworkers site has a great description of the process with a link to buy a kit from the Windsor Institute.
All the recipes I've come across recommend steaming the wood one hour per inch of thickness. Ash and oak will practically bend over backwards because of their large open pores. Straight-grained wood is also recommended; material almost always snaps at knots or curvy grain. When the wood is ready, you'd better be too. It only retains its pliability for a minute or so, meaning it's best to be hyper-organized. The material is swiftly bent around an MDF (medium-density fiberboard) form of your desired shape. Clamps are then applied to hold the wood in place for at least 24 hours. To prevent "springback" (not to be confused with springbok, South Africa's national animal) woodworkers often build second "drying forms" that allow air contact to dry the wood's surface area.
While steam bending isn't the only way to bend wood, I've found it to be the most fun. Woodworkers also practice laminate bending (thinner, more flexible strips of wood are glued together then bent), kerf-cut bending (small slots are sawn in the underside of the bend providing flexibility) and hot-pipe bending (damp wood is bent around a hot metal pipe). But enough of this wood bending wordplay — It's about time I let off some steam and went on a bender...
Johnny is currently blogging his experience as a student and amateur woodworker. You can keep track of his projects on his blog, Woodlearner.