Turn wood

As a handyman you get to do it over the years with a lot of work - from designing and creating new elements to renovation, modernization and restoration. Especially when working with wood, DIY enthusiasts quickly face seemingly great difficulties, namely the bending of wood. In fact, bending wood requires not only a great deal of specialist knowledge, but many years of experience ensure almost perfect quality. But at some point a beginning must always be made, so we explain the bending of wood below.

For bending wood a wide range of technical literature

Bending wood has always posed great problems for people. So it is not surprising that there is not only a high degree of technical literature, even scientific papers are extensive. This has the advantage of being on well-managed terrain and finding plenty of reading that really helps.

Thonet bentwood principle

Especially the Thonet principle is what you will come across again and again. Behind it hides the German furniture maker Michael Thonet (1796 to 1871). The main problem to be solved is that when bending wood, the inner side is compressed and the outer side is stretched and pulled. Therefore, especially on the outside is to be expected with the tearing of the wood. Michael Thonet has been working hard on bending wood.

An almost 200 years old technology still up to date

So it is not surprising that the Thonet principle of 1830 named after him is still of the utmost importance today. You can apply it for bending different woods.

  • solid wood
  • Plywood (laminating)

To implement this principle, various tools are needed.

  • hot water vapor
  • a steel band (bending band)

You have to know that about wood

First, the lignin contained in the wood is dissolved by the hot steam so that the individual cells can be shifted against each other - because that's what happens when bending. So that the wood does not tear on the outside, it is stretched into the steel bending band. Thus, the forces responsible for the tearing are largely dissipated to the metal band. The fact that these forces can only be partially dissipated, in turn means that you can bend a maximum of a radius that corresponds to 30 times the thickness of the wood.

Heat in the steam

Even heating in steam should be a problem for many craftsmen. The minimum temperature must be 93 degrees Celsius, otherwise the lignin will be insufficiently softened. The optimum temperature of the hot steam is exactly 100 degrees. Accordingly, your steam chamber must be very well insulated. But: under no circumstances may pressure be created by the steam in the steam tank. That means you have to maintain the exact temperature of 100 degrees while avoiding overpressure.

The right wood moisture

Of course, the wood moisture plays a big role. Conventional (construction) wood, as you get it at the hardware store, usually has a moisture adapted to the environment, which is called air-dry (lutro) between 20 and 30 percent. In the interior of houses, the water content can fall to 6 to 10 percent (central or furnace heating).

The most important factors in timber bending

The optimum humidity range for bending wood is also between 20 and 30 percent. The exact moisture content in turn depends on other factors.

  • Species
  • Bending and processing temperature
  • Degree of bend

In summary, it can be stated that the perfect combination of temperature and humidity leads to an extremely high bending result.

The wood bending in itself

The bending itself is not that hard. The wood is bent with the bending band into the desired shape and then fixed with screw clamps. Laminated wood is laminated during this process, ie glued and added layer by layer. Then the wood is time-consuming dried in the mold to maintain the bending shape.

Suitable woods

Of course, you also have to know a lot about the woods. Not every wood is equally well suited. Basically, harder woods (not forcing hardwood!) Are better to bend. The softer the wood, the harder the bending. Species containing many tannins tend to darken reddish discoloration at the bend. Subsequent woods are especially well suited.

  • beech
  • Oak
  • ash-tree
  • elm

More difficult to bend would be cherry or maple, but also tropical woods, although eucalyptus and bamboo are again relatively easy to bend.

Tips & Tricks

Before you tackle difficult wood bending projects, you should first familiarize yourself with the material and work techniques. In hardly any other crafting field is experience as important as bending wood. After all, each tree trunk within the same species of wood is an individual wood, as it differs by region, weather, age, density of many other aspects and even the time of beating. If you have the chance to look over the shoulders of a real professional, you should definitely accept this offer. Softwoods have a significant difference in density to hardwoods and therefore need to be bent transversely to the fiber.

Video Board: Woodturning - Log to Bowl