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Steam bending is the process of using steam on wood in order to make it more flexible. The wood can then be bent around a mold, which will give it the desired shape. Steam bending is a common method employed in woodworking, and is frequently used in fields such as shipbuilding, furniture making, and musical instrument construction.
The science behind steam bending is that the heat softens the wood's hemicelluloses, which are polymers found in it. Since these hemicelluloses have resin-like properties, when they soften, the piece of wood can be bent. Some of the more common woods used in steam bending include oak, ash, mahogany, and walnut. In general, hard woods tend to bend more easily than soft woods.
A steam box can be used for steam bending. This is a specially designed container into which wood is placed, in order to achieve maximum results. The size of steam boxes can vary according to the type of wood that is to be used. Many times, wood is soaked in a water solution before being added to the steam box. This makes the wood moister, and when the heat in the steam box draws this moisture out, it becomes more flexible.
Steam boxes are usually not airtight. Steam enters the box through one end, and on the other end, a small hole is drilled so that excess pressure can escape. The amount of time a piece of wood is placed in the steam box generally varies according to its size and type. A general rule, however, is that the wood needs to be steamed at a ratio of one hour for every inch (2.54 cm) of thickness of the timber.
After the wood has been steamed, it is generally removed from the steam box and placed into a jig-type device. This fixes the wood in place, allowing it to be bent in the desired direction. Molds may also be used in order to give the wood a specific shape, and are often employed when the same shape has to be made many times. Sometimes it is necessary to bend the wood as quickly as possible once it is removed from the steam box, since the steam-induced flexibility of the wood may dissipate as the wood becomes dry.
Steam bending has a long tradition in the history of woodworking. It is believed that Vikings were the first to use this method. Steam bending was an ideal technique for producing the curved wood needed for their boat construction.
@pleonasm - Wow it would have been amazing to see someone steam bending wood in person like that.
I would love to be able to build a boat from beginning to end. I think it would be more satisfying than restoring a car, somehow because you'd know each piece of the boat originated with you.
I've seen a few steam bending wood videos online and I think one day I might actually give it a shot. It doesn't look like it would be that difficult, once you have the right set up.
But, you'd need a lot of space in order to get started and right now, I just don't have that available to me. One day though, I'll hopefully get the chance.
@croydon - There are some beautiful (and some crazy!) furniture designs out there using steam bending, but my favorite application of it is always going to be in building boats.
I had an uncle who was slightly obsessed with boat building, I guess the same way that other people are obsessed with fixing up old cars.
He told me that steam bending is one of the best and only ways to get the right shape, but that unfortunately it can make the steam bent wood weaker, just by the very nature of what it does.
So you have to be very careful to keep that weakness to a minimum.
Unfortunately he passed away when I was quite young, so I didn't ever get to help him, although I did get to watch and that's when he passed on his advice.
There are some amazing pieces of modern furniture that have been made with steam bending. If you have a look online with a google picture search you can see some of them.
They tend to be quite expensive though, I think because the "classic" look at the moment is to only use wood, or at least make it look like there is no other material involved, and that takes quite a lot of technical expertise.
In fact it was only in 2004 that advanced steam bending techniques were pioneered by a design student. We learned about it in a business class as an example of innovation.