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How is steam-bent wood produced?

Heating the wood under steam softens the lignin, the natural ‘glue’ that holds the fibres together in the wood. The wood can be pressed around a mould using bending machines and tension straps or, depending on the dimensions, by hand. When it cools down, the lignin hardens again and the bentwood retains its new form. To ensure the wood remains stable during the drying process, special equipment, regular checks and, above all, a great deal of experience are required.

Our projects with steam-bent wood >

Bentwood has a long tradition

The technique of bending wood using steam and heat has been used for centuries and is thought to have originated in boatbuilding. It was first used on an industrial scale around 1840 by Michael Thonet. He used tension straps that prevented the wood from stretching along the outer radius, thereby avoiding cracks. Thonet developed moulds and machines to achieve high repeat accuracy.

By using steam-bent wood in furniture making, he was able to use fewer parts in his chairs and work with smaller cross-sections. This reduced wood waste.

The term ‘thermoformed wood’ is also used in some literature but is the same as steam-bent wood.

Steam-bent wood simplified furniture making. Chairs became lighter and therefore easier to ship. In the process, Thonet also developed a completely new functional aesthetic that turned the Viennese coffee house chair into a world-famous design classic that continues to inspire designers to this day.

Strengths of steam-bent wood

Because the wood grain follows the curve during bending, steam-bent wood is more stable and durable and has a nicer texture. The much less attractive alternative would be to assemble and glue together individual wooden parts.

The advantages of bentwood – its flexibility, its stability and the organic flow of the grain – are still appreciated today. Steam-bent wood offers a wide range of possibilities for design, architecture, interior design, public furniture and timber construction. Countless other applications are conceivable and feasible.

Steam-bent wood makes
many things possible

The limits of bentwood have by no means been reached yet. For example, the ratio of timber thickness to bending radius (often given in the technical literature as 1:5 or 1:10) serves only as a rough guideline. In our wood-bending workshop, we have succeeded in bending wood with a thickness of 50 mm to an inner radius of 0 mm – in other words, a full 90-degree bend.

What is feasible in terms of length and cross-section is limited by the workshop equipment and the availability of wood in the required quality. We can currently bend lengths of up to 4.5 metres. With timber thicknesses of more than 80 mm, the greatest difficulty lies in sourcing wood that is of good enough quality.

Widths of up to 300 mm are easily achievable with our presses. For designs that go beyond the usual parameters, we take a highly creative approach to finding solutions and constructing special setups.

Which types of wood are
suitable for steam bending?

In theory, all types of domestic wood are suitable for bending. However, not everything is possible with all wood types. Every wood has its own special properties that need to be taken into account. We process ash, beech, oak, maple, robinia, alder, chestnut, walnut, black walnut, apple, pear, cherry, iceberry, plum, poplar, willow, larch, Douglas fir, silver fir, spruce, pine and many others.

As a general rule: The harder the wood and the more uniform its density, the more suitable it is for bending. From this, it follows that spruce and pine, for example, are poorly suited for bending wood due to their low and uneven density. On the other hand, the equally light but more even silver fir can be bent well with larger radii. Steam-bent silver fir and larch are being used increasingly in timber construction in particular.

We can also steam bend exotic types of wood. However, sourcing air-dried wood for these species is often difficult. They also tend to develop buckles and creases caused by compression on the inner radius. Although we can remove these with appropriate reworking, changes in the grain pattern often remain visible.

We are always happy to carry out bending tests with the desired radii and types of wood.

How we process bentwood

Whenever possible, we bend the wood directly to the desired finished dimensions. This works very well with large radii and small cross-sections. However, reworking is often necessary, whether to remove bending marks or to shape and profile the bentwood parts. We are very well equipped for this manual reworking and have the necessary experience.

For complex, three-dimensional shapes, we work with long-standing partners who use CNC to mill the final profiled form from our bentwood components.

Sustainability of
steam-bent wood

Nachhaltigkeit von dampfgebogenem Holz

Wood stores carbon absorbed from atmospheric CO2. Using bentwood therefore keeps this carbon locked away. The longer wood remains in use, the longer the carbon stays stored. Today, wood is increasingly replacing environmentally harmful materials such as plastic, concrete and steel. This is referred to as decarbonisation.

The aim of sustainable wood utilisation should not only be to use wood whenever possible, but also to build for the longest possible lifespan. Energy flows into every object and piece of furniture during production and transport. By extending the service life of products through stability, we also improve their energy balance.

During steam bending, we steam the wood and heat it to more than 100 degrees. This kills off fungi and bacteria, making the bentwood less susceptible to rot and thereby increasing its lifespan.

Thanks to bentwood, outdoor furniture (e.g. curved benches) requires less gluing – or none at all – and has hardly any open wood pores through which water can penetrate. This also has a positive effect on its service life. Furniture made of steam-bent wood is more robust and more durable than glued wood, thanks to the continuous flow of the grain.

In our consulting and development work, we place great importance on structural wood protection. With the right choice of wood and targeted surface treatments, we can ensure that the end products have a very long service life.

 

 

Our commitment
to the environment

We source most of the wood for our steam-bent wood projects from forests within a 15-kilometre radius of Felsenau. We mainly work with Swiss wood and have been awarded the HSH label.

We obtain the energy for steaming and drying from our wood heating system, which we run with wood waste. We prefer suppliers with short travel distances, and we support innovative bentwood design projects with the aim of bringing furniture and wooden product manufacturing increasingly back to Switzerland.

Steam-bent wood is highly versatile

Steam-bent wood has been used for centuries in boatbuilding, wine barrel cooperage and the construction of carriages and wagons (wheelwrighting). Thanks to Thonet, bentwood found its way into the furniture industry around 1850 and is still used there to this day, especially to make chairs and tables. 

It is also known for its use in sports equipment, such as the Davos sledge. For a while, skis were also made of steam-bent wood. Other applications include walking sticks, broomsticks, coat racks and clothes hangers. For public furniture such as curved benches, we are increasingly allowed to use steam-bent wood due to its beauty and robustness.

In interior design, architects and builders use bentwood for skirting boards, curved counters, edges and finishes of all kinds. We also use steam-bent wood as frames for round windows and portholes. In instrument making, many drums and drum frames are made of steam-bent wood.

The use of bentwood is also becoming increasingly important in timber construction, such as for façades, pergolas, arches and various solid wood structures.

For curved stair handrails, steam-bent wood helps to minimise the number of joints. Since handrails are both seen and touched, the wood’s warm and uninterrupted naturalness is a particular benefit.

We also bend wood to create jewellery. Luckily, inventors, creators, designers and architects never run out of ideas for how to use this beautiful material. The Winkler wood-bending team looks forward to every new bentwood idea and provides support at every stage, from planning through to installation. Our greatest challenge – and one of our greatest joys – is to constantly push the boundaries of wood bending and keep this ancient craft alive.

 

 

References

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