When Sarah first put some references of potential stock in front of me, one image stood out immediately. It was a circle arch and we both were equally excited and horrified when we knew what it meant. How were we supposed to make it out of timber? Luckily, we both knew the answer: steam bend it!
When we were prop students at NIDA, we had been subjected to the somewhat ‘experimental’ techniques of steam-bending, during the furniture component of our woodwork module. It was a challenging and ambitious course that was renown for sorting out the students’ woodworking skills and both Sarah and I had been given the daunting task of using timber steam-bending to fulfill the components of our respective chairs. I say ‘experimental’, because as far as we could tell, none of the students before us had really used or selected chairs that needed to have steam-bent components, nor had the teachers had an extensive working, practical knowledge of the technique. To be honest, I had never really considered that wood could be bent, not in a non-industrial capacity, anyway.
Needless to say, we forged on with the research and gathering of components for steam bending our chairs. Firstly, we needed to know and understand that the material characteristics of some timber means that not all timber is suitable for bending. Timbers can shatter and split along the grain with heat and cannot sustain the pressure and force applied in forming jigs. Secondly, we needed to work out the process involved in the steaming and bending of timber.
In order to saturate and soften the lignin inside the fibers of the timber, you need a constant and sustainable temperate of steam from a steady and stable source. Essentially you are softening these lignin polymers for a certain time, subject to the thickness of the piece of timber you are trying to bend. Generally, you are looking at around an hour of steaming per 25mm or so of timber thickness, but one shouldn’t think that you are going to achieve a ridiculously tight bend, nor should you risk it! Since we had limited resources and time, we were advised to laminate our timber from thinner sections, which were easier and more pliable under these pressures.
Oak, maple, ash and birch seem to be the best hardwoods to use for steam-bending and spruce and fir for softwoods. Sarah used a European species of beech for her chair, while I selected Queensland Ash for mine. For the Heartwood Arch, we chose American Oak, which has a long history in steam-bending and is durable, while having a nice finishing grain.
The steaming vessel is a little trickier. You need to know the eventual size of the pieces you are steaming and that you can distribute the steam evenly throughout the box. You also need a constant and steady supply of steam which can maintain its temperature. After experimenting with various boilers and kettles, we managed to buy a cheap wallpaper steamer that needed a little hack to attach it to the box itself. Plywood will do for the box; we were fortunate to have a little bit of marine ply left over from a job to make the box with, and then hinging a small door on one end for access to the timber. Using this setup, you can heat the box up to nearly boiling temperature and supply a steady source of steam for around an hour and a half, which is enough to bring the inside of the box to sufficient bending temperate and maintain it for an hour. Propping (no pun intended!) up the box and making a draining hole in one end allows the box to be kept clear of pools of condensation gathering in the box. Oh, and a thermometer for accurately gauging the temperate is recommended.
Stay tuned for part 2 next week!
Tom
