Steam Box

In bending wood, the wood needs to be immersed in steam. A variety of boxes have been designed to put the steam around the wood. Probably the most common is to use pipe of 3-4 inches diameter with bamboo skewers or wire fitted into holes near the bottom to create a shelf to support the wood. A box can also be built of wood. One popular steam box design is to use rigid fiber insulation (the type with foil on one side) to make a box - the insulation ensures that heat is retained in the box and is uniform along the length. Others have used rigid polystyrene foam insulation.

Steam can be introduced into the box from one end or from the middle. One advantage of adding steam at the middle is that the hot steam travels a shorter distance to the ends and will cool less. This will help ensure a more uniform distribution of heat. If the steam box has a slight slope towards the middle, any condensing water will drip back into the steamer to be reheated.

Sources of steam can be:

• electric tea kettle
• tea kettle heated by a camp stove
• wallpaper steamer

Wallpaper steamers, such as those sold by Wagner, produce a lot of steam and are well regarded.

It is important to supply a shelf to support the wood in the steam box. This is often a set of wires which cross the box above the bottom, allowing steam to surround the piece and keeping the piece in the top part of the box, where most of the steam "hangs out".

Effective steaming requires that the temperature be very close to 100°C (212°F). If it is cooler, the wood will not heat sufficiantly and will not bend easily. Use a thermometer to check the temperature while steaming. Ensure that the steam will flow through the steam box. The point where the steam is introduced should be reasonably sealed and the other end(s) should be vented. A heavy rag can make an effective control for the vented end - just drape enough over the end to control the amount of steam alllowed to escape.