What is Steam Bending?

How it works.

Wood is comprised of around 50% cellulose, and 30% lignin. Cellulose is in the form of hollow, tubular cells rather like straws. Lignin is a natural thermoplastic which acts like a glue binding the cellulose fibres together. When the lignin is softenend by applying heat it allows the cellulose fibres to slide, so the material can be squashed, twisted, and stretched into new shapes. When the material cools down the lignin “sets” again, re-binding to the cellulose, meaning the wood will (more or less) retain the shape it has been bent into.

Why the connection between green wood, and steam bending?

Green woodworkers often use steam bending as a way of creating new and interesting shapes and components. There are several reasons for the synergy between the two techniques. Firstly, due to the fact that when wood is green (unseasoned), it has a higher moisture content, and this makes green wood softer and more flexible, so tighter bends are possible. Another reason is that for steam bending to be succesful, it is important that the grain (fibres) run parallel to the edges of the wood. Short grain, ie grain that cuts across the length of the component, are likely to fail when bent. Because green woodworkers split their components along the grain, rather than saw them, there is a much higher success rate in bending. Finally, counter-intuitively, the steaming process actually drives moisture out of the wood, effectively partially kiln drying the wood. This is a distinct advantage to green woodworkers and saves on drying times. By using thoughtful construction methods, it is possible to make furniture very economical in terms of timber use. My Trefoil Table is a good example of this, using lightweight components to achieve a strong, elegant design.

Introduction to Steam Bending Course

There are various techniques we teach during our two day steam bending course. As well as learning the science, theory and techniques for making the bends, we will cover timber selection, steam boxes and steam generation, formers (to bend pieces around), compressions straps, (to increase the radii you can achieve), and various other jigs and devices that can simplify what you are trying to achieve.

If you are looking to source timber for green woodworking, or steam bending, check out this blog post about sourcing sustainable timber in Devon.