When we fully enter the world of carpentry and DIY, one of the tasks that at some point must be faced is bending or curving wood.
There are different methods to bend wood, which you can adapt to the type of project you will develop and thus obtain an original result quickly.
Decreasing the hardness in a piece of wood is achieved through softening, making the carving or carving work to be carried out easier. At an industrial or artisanal level, various pieces of furniture or wood are made that need to be softened to give them the curvature they need.
In the art of carpentry and cabinetmaking, it also becomes necessary to soften the wood to create various pieces of wood used to construct bentwood furniture, houses, and boats, among other things.
Many constructions require adaptations to the various hydrodynamic and ergonomic requirements, so it becomes useful to know some methods that serve bentwood.
In this article, we will explain some wood bending techniques, which you can adapt to the type of project you develop and thus obtain an original result quickly.
Using steam to bend wood
Steam bending is a process of softening wood fibers with a combination of heat and moisture until they are flexible enough to bend. Hot, wet sticks are drawn from a steam box and quickly wrapped around a curved shape.
Steaming and Boiling are the most common methods. The steaming method is carried out in a bucket, and the increase of steam and pressure obtains the high temperature; in this way, the treatment time is less. In the boiling method, the temperature must necessarily be raised, and this method is easier because it is slow.
The surface of the wood, before bending, must be perfectly smooth, not only because it is easier to machine before bending but also because surface irregularities can lead to the formation of roughness in the wood. Once the wood is prepared, the method of curving by vaporization can be applied.
The steaming method is carried out by introducing the prepared wood into a steam stove. In this stove, steam is injected at a temperature of 180 to 212°F, maintaining it for approximately 1.8 minutes for each mm of the thickness of the wood.
To make wood plastic and compressible, it is necessary to treat it with steam and heat.
It has already been indicated that wood with 25 to 30% humidity contains enough water to be compressible when heated; In addition, the contained water facilitates the internal heating of the piece.
Most laboratory tests show that bending qualities are not improved above the boiling temperature of water 212°F.
Probably the most common and most adequate method to obtain the required conditions is to submit the wood to the action of saturated steam at atmospheric pressure in a stove.
The essence of the stove is that enough steam enters to maintain an average temperature of 212°F and that there are devices to insert and remove the wood quickly.
The wood inside the stove is placed in ponds. It should be remembered that some wood, such as oak, stains in contact with iron or steel.
To save steam, the stove must be thermally insulated. There is no interest in using high-pressure steam, as bending properties are not improved above atmospheric pressure. High pressure also has several drawbacks.
The stove must be much stronger; Before opening the door, you have to make sure that the pressure has dropped to 1 atmosphere, which forces you to waste time; It has also been proven that high pressure damages some wood and even stains it.
Pros and cons of steam bending
It is important to note that this technique is still handmade; For this reason, it is expected that it is used mainly to create small or medium-sized objects, with the large ones being more difficult but not impossible.
The great advantage of steam bending is that it allows the strength of the cellulose fibers to be preserved, guaranteeing a long-lasting, high-quality product.
The new generations, accustomed to a world whose technology evolves at a gallop, could imagine that there are more sophisticated techniques for it.
But the reality is that today the tradition is still maintained in certain procedures since the results continue to be excellent in the long term. The best example is the versatile and durable curved wooden boards.
Using sheets to bend wood
And if I do not have the means to do it in the previous way, how to bend wood? Well, the answer is not complex, using plates.
The wooden veneers, 1 or 2 millimeters thick, are very flexible and do not split unless we force them excessively, which is why they are an ideal option for obtaining curved wood. The process is very simple.
We apply glue on the sheets and all the faces inside the piece, and we do not make sure that the surface is well-impregnated.
We join them until we get the desired thickness, being careful not to go too far since, with each sheet, the resistance increases.
We fix the union of sheets to the mold using the presses.
We wait for it to dry. With this method, it will not be necessary to wait more than 2 or 3 hours, although depending on the glue used, it may take a little longer.
Do not use very fast-drying glue since it can take several minutes to finish applying it and at least another couple to fix the presses.
Glued Laminated Wood
Glued laminated wood, or Glued Laminated Timber (Glulam), is a structural material manufactured for the union of individual segments of wood glued with industrial adhesives – generally melamine or polyurethane resin adhesives.
The resulting pieces provide high durability and resistance to humidity, capable of covering large spans and building unique shapes.
Many carpenters use glue to bend the wood. The way they do it is they apply glue to the laminated wood boards and bending the wood before the glue dries.
The wood used must be fine, and it is not convenient to use normal wood glue. Not ideal for the process. Instead, use epoxy. It is very effective but expensive.
Bend Wood with Kerf Cuts
Kerf bending involves sawing a series of deep notches through the grain to weaken the stock. After notching, the thin top layer that remains is flexible, allowing for flexing to be done.
After folding, the action is quite brittle and must be supported. As you’ve probably concluded, cut flexing is impractical. Kerfs are quite distracting and, even if hidden, telegraph across the face of the curve.
Also, the stock is severely weakened and has no structural integrity unless the pans are later filled with wood or epoxy. Even so, this adds to the visual distraction.
If you need to create a wide curved panel without the time and fuss of laminations and the inherent weaknesses of kerf flex, a better solution is flexible plywood.
Bending wood with chemical
There are other bending methods based on the chemical treatment of wood, such as immersing the wood for a few minutes in a liquid anhydrous ammonia bath.
Wood thus treated can be bent until the ammonia evaporates, when the wood becomes hard. The problem with this system is the cost; this bending method is not well known and only use for special purposes.
Bend wood with water
How to Bend wood with water? By submerging it in water, wood can be bent in one of the most frequent ways.
Look for wood that is neither too thick, too hard, nor too thin. If it is, it will be hard to bend or break. Wood about 20 mm thick would be the best choice. The best choice is also wood with a straight grain.
Check the wood’s moisture level. The best wood for bending has between 20% and 30% moisture level.
Find something waterproof to put the wood in so it can soak. It should be able to hold the water and the whole length of the wood you are bending.
Wood needs to soak for 24 to 48 hours, and a wood moisture monitor should always be used to check for moisture. Putting the wood in hot water helps the process move along faster.
Take the wood out of the water and place it on the mold. You will need to use clamps or bolt-on clamps to hold the wood against the wall of the mold.
Now, the wood needs to dry out. Keep an eye on how much water is in the wood. It can be taken away when it returns to its original moisture level.
Once the wood is dry, you can take the clamps off and use them.
Things to Keep in Mind When Water Bending Wood
To water bend wood, carpenters soak the wood in water for days.
Then, when the wood is flexible enough, they fix it in a mold and keep it that way for days. Afterward, the wood will be curved and ready to be used.
However, as with everything, the theory is always easier than proof. There are multiple considerations if you are going to water bend wood. Such as:
Wooden boards that are too thin can easily break if you try to bend them with water. On the other hand, boards that are too thick can be difficult to bend.
Choosing a medium-thickness piece of wood is best for the best results.
Some carpenters prefer to work with less than 3cm thick wood, and others have no problem with thicker slices. It depends on your experience.
Type of wood
It’s not news that some types of wood are easier to bend than others. They tend to have open veins, which allow water to seep in and soften the fibers.
If your project doesn’t require a specific type, you should look for flexible wood. For example, white oak, beech, and elm bend easily after soaking.
There are also a couple of other types that bend well, such as hackberry, hard oak, pecan, and ash.
Some woods bend well but discolor, like walnut, so if that’s going to affect the quality of your project, avoid them.
The direction of the grain can make a big difference when it comes to bending wood. Wood with a straight grain is known to be easier to bend.
Straight grain means that the wood grains are parallel to the vertical axis. So the chances of the wood splitting are low because you’re bending in the same direction as the grain.
Cross-grained wood is more likely to break because the grain can split when it is bent in another direction.
Avoid bending the wooden boards that come from the center of the tree. These are more prone to breaking.
Container Size & Heat Tolerance
size, heat tolerance, and water resistance should be large enough to quickly move the wood in and out.
You should also remember that you will need to keep it on a hot plate for days, so choosing a suitable size is essential.
Aside from size, you also have to consider heat tolerance.
As I’ve mentioned briefly, the container will sit on a hot plate for a couple of days, so making sure the material doesn’t warp is essential.
Other materials with high heat tolerance, such as stainless steel and nickel, also work.
After considering size and heat tolerance, you have to consider water resistance. The container will be full of water for days, which often takes its toll on the material.
Copper does not oxidize under water. It is commonly used for underground pipes, making it a suitable option. There is also nickel and aluminum: both resist water well.
Wood moisture level
Before attempting to bend the wood, check its moisture level. Wood boards with moisture levels of 25% are ideal for bending and will be easier to work with once soaked.
A slightly lower or higher level is also fine, but ensure the humidity level is not too low.
The humidity level cannot be less than 10% because the wood could burn. It also can’t be too high because that will cause it to become soaked.
The easiest way to check the moisture level of the wood is by using a moisture meter. This model would be perfect. It is very reasonably priced yet provides an accurate reading time after time.
You can substitute the oven method if the money is tight.