Steaming is an effective method of softening or plasticizing wood (known as steam bending wood) so that it may be molded for craftsman and industrial applications, such as the manufacture of furniture and boat parts. Experts approach this method differently, depending on the type of wood grain and the quantity of the material involved in the project.
The timed process involves placing wood scraps in a box, which is supplied with heat via a steam generator. Once the wood pieces are steamed, they are pliable and immediately ready to be shaped during the second part of the steam bending process, with the aid of a jig and other shaping equipment.
Best Wood For Steam Bending
Is there an ideal wood for steam bending, assuming you had a project where you could choose any wood?
Michael Dresdner: There are many woods that work well, including (but not limited to) hickory, oak, ash, and yew. Is that enough to get you started?
Simon Watts: There are quite a few timbers that are amenable to being bent with the aid of steam. Among hardwoods I would put ash, most of the oaks, hickory, black locust and beech in the top form. The only softwood I know that bends well is hackmatack–also known as tamarack or larch. The moisture content of the wood is critical–the greener the better. If you can only get kiln-dried stock, prolonged soaking in salted water restores some, but not all, of the bending properties.
Rob Johnstone: I’ve never had a hardwood refuse to bend when I used steam as an aid. I’ve also never really had a great steam bending experience. It is a putsy and annoying technique from my perspective. With that said, what makes a hardwood ideal for bending is straight running grain with a minimum of flaws, and a moderate specific density.
How to Bend Wood: 6 Steps
1. Choose a wood species
All temperate-zone hardwoods (chart below) steam-bend well and, in general, bend better than softwoods. Steam-bending other temperate-zone species is possible, but limit their use to gentle bends. Among tropical hardwoods, mahogany gives acceptable results. The brittleness of highly resinous tropical exotics make them unsuitable for bending.
2. Select your stock
Regardless of the species you use, careful board selection increases chances of successful bends. Choose straight-grained lumber without knots or other defects and avoid decay (even slight spalting). The grain should run parallel to the edges of the workpiece or “run off” the edge at a shallow angle (maximum of 1″ slope to 15″ length). The greater the run-off angle, the more likely the piece will break when bent. Splitting wood from a larger straight-grained billet guarantees straight, parallel grain but is not always practical.
3. Machine the parts
Straight stock runs through a planer or jointer easier than bent pieces, so do as much sawing, surfacing, or shaping as possible before bending. Surface irregularities can cause splintering, so remove rough saw marks. Holes or mortises distort or they cause the part to collapse or split; perform these operations after bending.
4. Make a steam box
Steaming takes about one hour per inch of workpiece thickness and parts must stay on the bending form for one hour, so unless you make more than one form, the steam box only has to accommodate one part at a time. For efficient use of the steam boiler [Sources], a steam box should be only large enough to hold the part blanks with room all around for good circulation. For tight bends on thick parts, increase box size to accommodate resteaming a partially bent piece. The steam box shown in [Drawing below] holds two leg blanks for the desk (shown above) and accommodates resteaming of a partially bent leg.
5. Build the forms
Make bending forms from particleboard or plywood laminated to a thickness equal to the width of the bending blank. Bending a workpiece puts considerable stress on the form, so when in doubt, more form width beats less every time. You’ll never be disappointed by a tendency to overbuild.
6. Steam and bend
Securely clamp the bending form to a sturdy workbench. Have all clamps handy. Bending should be accomplished within five minutes after removing the blank from the steam box so you may want to rehearse your procedure.
How long do you have to soak wood to bend it?
Of course, wood moisture also plays an important role. Conventional (construction) wood, as you get it in the hardware store, usually has a moisture that is adapted to the environment and is called air dry (lutro) between 20 and 30 percent. In the interior of houses, the water content can drop to 6 to 10 percent (central or stove heating).
What is the best wood for bending?
The most plastic, and therefore more suitable wood for bending, are deciduous species of wood, such as birch, beech, oak, hornbeam, ash, maple, linden, poplar, alder. Coniferous species are used less often. (pine, cedar and larch). For the manufacture of bent glued blanks, birch veneer is best suited.
Which wood is best for bending?
Just about any wood can be successfully bent depending on how patient you are so there is no “best”. I would, however, avoid some species if this is your first attempt. Those are species that have open, short grain such as oak.
Rather than trying to bend something full thickness you might consider doing a laminate- using multiple veneers bent and glued into a form… a higher grade of plywood, as it were. This is actually pretty simple and will eliminate the need for a big vat, gallons of water, and lots of heat. Do a search for vacuum bag veneering.