The process of wood steam bending involves exposing wood to steam, making it pliable, and then shaping it accordingly. When the wood cools down, it will take on a new shape. The generally accepted steam bending procedure is done using a steam block box and a former to bend the wood upon.
Steam bending presents low energy, ecologically and economically viable method to manipulate wood. There is no expense attached to the process for the drying time of glues. You will also find that this process generates less scrap since we can bend smaller pieces into shape rather than cutting a shape from a larger wood piece.
We apply steam bending techniques in various fields like shipbuilding, the manufacture of musical instruments, and furniture. We also use the steam bending technique to make tennis racquets and other such sports equipment.
There is not much on record about the history of steam bending of wood, but the first patented technique was recorded over a century ago in England. In the US, wood steam bending was done as early as 1794.
In this post, we take a close look at the various techniques of bending wood. We then consider the best types of wood for or bending and some of the applications for which wood can be bent. So, let’s jump right in!
The Best Wood for Bending
If you want to bend wood, you have to choose plastic-like timber. Most of the wood suitable for bending comes from deciduous trees like birch, hornbeam, maple, alder, oak, ash, and poplar. We use coniferous species like pine, cedar, and larch less often. For the manufacture of bent glued blanks, birch veneer is best suited.
Based on the bent wood requirements, the table below features different types of wood and their varying degrees of “bendability.”
How to Bend Wood
There are a few different ways to bend wood. The choice of bending method depends on different factors like the purpose of the bent wood, climatic conditions, and wood bending equipment availability.
Bending Wood with Steam
Wood is exposed to steam in a steam chamber to a temperature of 100°C. We then clamp the wood in a mold in hot conditions and bend it to the required shape. We then leave the wood to cool down and dry. Once the wood cools down, the new, bent shape will become permanent.
It takes about one hour for each 25 millimeters thickness of the wood. So, you want to steam wood using 30% humidity and an initial temperature of 25°C, the time taken will be one hour. If you have a wood thickness of 30 millimeters, then under the same temperature and humidity conditions, it would take 1 hour and 50 minutes to reach the desired temperature. Once the wood reaches 100°C, you have to be very fast in bending the wood.
Using Chemical Impregnation
This method works on destroying the lignin bonds that bind the wood fibers, making them more flexible. The main chemical we use in this process is ammonia. You have to soak the wood in a 25% aqueous ammonia solution for a few hours or overnight. After some time, the wood becomes pliable, and you can shape it with a mold.
Once you have completed the shaping operation, you must let the ammonia evaporate so that the form gets fixed. Leave the wood in a ventilated room to dry. Once the ammonia dries, you can remove the wood from the mold, and it will retain its new shape.
The Kerf Cutting Method
In this method, you have to make cuts in the wooden piece that you want to shape. You need to make wooden cuts inside the bend, but take extra care not cut to deeply as to break the wood. A table saw serves the best purpose for making the notches in the wood.
First, prepare a paper template. Then take a cross-sawn wooden board to bend the piece. The notches will be about one centimeter apart from each other, and you have to fill the grooves with glue. You may need to use a strap to tighten the pieces into the required shape.
You will also have to use clamps as required. Leave the wood for four to five days for the wood to dry. Once you remove the clamps, straps and fixtures, you will see that the wood becomes permanently shaped as required.
Here you have first to procure thin layers of wood that can be bent. Once you have collected the wood layers, pile them up together to form the thickness you want from the final piece. Now, use a template to bend the layers into the desired shape. Add glue and clamp the layers as required. Once the glue dries completely, the wood will remain in the new shape.
How to Bend Wood Using Water
If you don’t have a steam chamber or want to keep the process simple, you can bend wood using only water. The procedure is quite simple – you soak the wood in water, preferably hot water, for a few hours. Once the water soaks into the wood, it is ready for bending.
For the bending stage, you need to arrange a series of fixtures in conjunction with the size of wooden pieces you want to bend and the required shape. Once the wood dries, you can remove it from the fixture, and it will permanently take its new shape.
Wood bending is both an interesting and challenging woodworking activity. Many woodworkers shy away from the process of wood bending. It requires a lot of time and patience to get it right. As we have seen here, there are several different methods you can use to bend wood.
You will probably need to do a considerable amount of experimentation with different methods before getting it right. But if you persist at it, the rewards can be satisfying. Once you get the hang of how to bend wood, it will surely be worth the time and effort spent when you see your finely-shaped wooden items.