Why Bend Wood?
Wood is often intentionally bent in order to make or create objects with curves. Furniture is a common example for this.
Knowing how to bend wood will open many opportunities for woodworkers that before could only work with right angles.
Before I get into the most common and best ways to bend wood, you need to know something up front. Straitening wood is an altogether different concept.
Knowing why wood naturally bends will aid in preventing unwanted abnormalities.
Most Common Ways To Bend Wood
I will detail some of the more common methods found in this process. Yet I wish to begin with the most successful method. Luckily it is also the easiest to achieve and yield consistent results.
Education in woodworking classes can be found on this topic if you desire. There are artists who specialize in these techniques that also freely share some information.
Steam Bending Wood : The Most Successful Method
It may surprise you that steam bending wood is often the best route to go with. It yields the best results time and again.
In order to achieve this you need some basic tools which are not expensive. After this combine the tools with some diy ingenuity.
The steamer is the most critical tool of this process. Without steam nothing else will work.
There really is no best model as long as the steamer you have works. Some like the Earlex Steam Generator.
You then need an enclosed environment to capture this steam. Many will construct a box or use pvc pipe and cap the ends.
I will go into this more a little later. There is a huge advantage to this part of the process with bigger projects.
You then simply need to send over the steam from the generator through the attachable hose and into the pipe or box. It really is that simple.
Why Steam Bend Wood Over Other Options?
Yes this steam bend method is better than soaking. Some of the greatest furniture designers have used this method for generations without fail.
It can test you, but be patient and learn its ways.
Of the greatest advantages is its ability to work with thicker pieces of lumber. The general rule is one hour of steaming for every one inch in wood thickness. This obviously will vary based upon wood density so experimentation is needed.
An additional advantage is that this method does not require complete immersion in water. Within a box built for steaming a form can be used in conjunction with clamping. Steam, then adjust clamps, steam again as needed while making adjustments along the way.
Notes Of Caution While Steam Bending Wood
The steam box does need proper ventilation. Holes should be drilled if self made that allows venting.
The temperature in the box should remain near 212 degrees Fahrenheit. This is the same temperature at which water boils.
Due to the nature of this process it is best done outside or within a space that can safely accommodate this like an open garage. Wear safety equipment within reason, gloves for example to handle these temperatures is a must.
Be aware that steam can and will burn the skin. When removing the wood from the steam box it too will be at the same temperature. Handle it with great care.
It would also benefit you to research the modulus of rupture and the modulus of elasticity of the wood in focus. You can gain an idea of what kind of moisture content may be required for your project at hand.
Soaking To Bend Wood
Another historically popular way to bend wood is through immersion in water. After wood is soaked it is more pliable.
This is best done with thinner pieces of lumber.
Once the wood is removed it can be applied to a form and clamping can be used. Still be aware that this process still requires patience.
It also may require the wood to be soaked more than once if the piece is too thick.
Typically for the average piece of wood you would need to allow it to soak for approximately 24 hours. The word average is very vague and there is not standard for this.
Density and thickness matter. Varied species alone create a variable in density which one will have to research and experiment with.
This method was very common within historical periods if not the most common way in those times. While effective it does have its own challenges depending upon the intended project.
The key to success is ensuring the wood is soaked completely through while allowing for patience in forming.
The Kerf Cut To Bend Wood
If you do not know what a Kerf cut is in this context allow me to explain briefly. It is a cut which removes material from the lumber while not separating the lumber into two pieces.
If the wood is a 3/8ths of an inch thick then the Kerf cut may remove ¼ of an inch of material while the last 1/3 remains in tact. This creates a slit in the lumber.
When these slits are cut in succession the wood bend can take place more readily in the direction to the side where the Kerf cuts were made.
How far you separate the slits will determine the degree of bend that you can achieve. The closer the cuts are, the more bend you will get. The further apart they are will yield a lesser degree of bend in angle.
This method has been common in some instrument making such as violins and guitars. While it is not the most effective method it does achieve the goal.
A problem which occurs is how the shape will often not be rendered exactly how one wishes it to be.
Heating To Bend Wood
A more primitive way to bend wood is to simply heat it. Yet this method is temperamental. The thicker the material the less effective it will be.
If one practices Shou Sugi Ban for wood burning you will easily understand what heat does to wood.
In more ancient times the heat method was used in arrow making. An arrow is thin enough to allow for heat to make the wood pliable. The arrow maker would then straighten to a form.
There is a side effect to using this heat method. Once wood heats the sugars within the timber harden.
This method was also a way to “fire harden” tools of more ancient times. Once the wood cools it becomes more difficult to manipulate.
If one is trying to achieve a greater degree of curve within a piece of wood this process is more likely to result in a break.
I have used this method for straitening small stubborn pieces of lumber, yet I never have used it for bending.
Considering this I would say that you may experiment with the idea yet remain cautious and within reasonable expectations. Using steam or water immersion is more effective by far.
What Is My Personal Favorite Wood Bending Method?
By far my favorite method is steam bending. I prefer using this over any other unless it is very small pieces of wood. If the pieces are small enough, as in fitting the wood into a tray, then I do not mind soaking.
Here is the cool thing about steam bending. You do not have to use a permanent box. Unless you are a dedicated maker of some item like furniture or musical equipment, you can create a portable steam box.
I have used basic 2×4 framing and wrapped it in heavier sheets of plastic often used on construction sites. It is not perfect. It will leak and the temperature can at times fluctuate.
Yet it is an easy fix to prevent needing dedicated space for the tool.
In using this method you can make it as big as you need with relative ease. There is only one question that you may need to ask. It is if your steam generator can keep up with the volume of the box to make enough steam at the needed temperature.
Drying The Wood After Bending
Once the bend is achieved you are technically half way to completion. The wood must dry and most importantly retain its shape. Here is where things get really tricky.
All of the above methods are great in telling you how to get the bend. Yet a good form goes a long way to not only achieving the bend, but also keeping it.
There are some complications in using a form. You will notice at times on larger pieces that after clamping the wood will twist.
Sometimes there can be pockets on the inside curve of the bend which did not conform as intended.
To aid in preventing this use as many clamps as you believe that you need. Some bends require more complex curves so it is done in stages adding clamps along the way.
Smaller pieces may be held by a wood vise in order to aid in drying and shaping. Some ingenuity can at times be required.
As wood dries it also will want to reshape itself. Water from immersion or steam swells the lumber. As it dries it looses mass and shrinks.
It is this shrinking process as it dries where things can twist and turn.
When drying attempt to keep steady and even airflow across the whole of the surface. Adjust clamping throughout the drying period. Airflow is far more important than heat.
Applying heat in an attempt to dry the wood can cause more problems than it will give you in solutions. Allow ambient temperatures to be natural and normal while simply keeping consistent and steady airflow.
Does Bending Wood Make It Weak?
Actually once wood is bent it tends to become stronger. This is due to the compression which takes place naturally within timber. Think of how a bow and arrow function together.
If you look at a cross section of wood you will see the heart at the center and its outer layers continue to expand to the bark. The outermost layers are more pliable. The heart is rigid.
Just as when a tree blows in the wind its heart keeps it from bending to the point of breaking. Yet it must bend with the wind. The outer layers act as natural springs relieving tension that would otherwise snap the tree in half.
The direction in which you choose to bend the wood in your making process should play on this very principle. Nevertheless in general terms when wood is bent it often will gain strength to that form when dried.
The one thing to note here is that this remains true as long as you remain within reasonable designs that allow for support. Exaggerated bends, poor designs, or geometrically unstable shapes will compromise the integrity of the wood.
Can Wood Be Reshaped To A New Form After Bending?
Yes it can be reshaped. There really is no limit to this as long as the previous bends were within reason for the wood you are using. What degree of bend that is considered to be within reason will vary with the piece of lumber you are using.
If the bend goes outside of its natural limitations then the wood will be somewhat compromised to a degree. The greater the bend outside of that limitation the more likely a break is to happen.
The one exception to this reshaping rule is when heat bending is used. As stated before when heat is applied the sugars within the wood will harden and solidify.
If you take a piece which has been fire hardened it is more than likely that it will break when an alternative bend is attempted. While this is not always the case, I will say that the thinner the wood is the more likely you are to have success with heat.
Which Method Offers The Best Looking Finish To The Surface?
Steam bending will yield the best looking finish to the wood surface after a project is completed. The steaming process is less invasive overall despite most methods being invasive by way of moisture.
No matter which method you choose, when using water as the tool the key is to move as quickly as the wood will allow you. In other words do not let your lumber soak for an additional day if it is not needed.
Continued exposure to moisture is not a good practice. It does impact the fibers and can in turn impact the later finishing process of the piece. By all means allow the wood to have what it needs and do not rush, yet also do not procrastinate.