ALU Chair

Five laser-cut aluminium sheets, bent in one direction only and bolted together. The construction is the form.

The Project

This was a project at University of Applied Arts Vienna in collaboration with HAY. As a starting point for the project I chose the Interstuhl 262S by Hadi Teherani to study and identify what makes it interesting and develop it into a sitting object through exploration.

Early on I realised that the Interstuhl only has 2D bends, yet it achieves pretty interesting and organic shapes where the bends create the geometry. I wanted to translate this quality and visual language into a more affordable product such as a living room or a café. During this project I did a lot of exploration on how to achieve rigidity through 2D bends and assembly. Laser cutting, bends in a single direction, simple joints. No double curvature, no stamping, no hidden reinforcement.

Interstuhl 262S chairs by Hadi Teherani around a boardroom table, their bent sheet-metal frames carrying the seat and back. — Interstuhl 262S, Hadi Teherani. The reference.

Exploration

In the kickoff week I rebuilt part of the reference chair to understand its shapes. Sketching throughout, I tried different bends and constructions before building small models.

Eventually I landed on 45-degree bends for the legs which I wanted to develop further. The interesting part is how the backrest is carrying on as an extension of the legs.

A cardboard model from the kickoff week, its seat and back stepping down in a cascade of simple folds. — Kickoff week, in cardboard.

A small aluminium model with the legs bent at 45 degrees, standing on cardboard. — The 45-degree legs, at model scale.

A sheet of chair sketches, several with the seat divided into four identical parts.

Experiments

Furthermore I explored different joints such as rivets, screws and spacers. I wanted the assembly to be readable. You should be able to look at the chair and understand how it goes together. Furniture screws + spacers won, partly because they let it be flat-packed and it gives the chair an industrial and honest aesthetic.

An aluminium rivet set through a strip of sheet, held in a vice. — Rivet.

Two strips of aluminium joined with furniture screws through a spacer, on a workbench. — Screws and spacer.

Full scale prototype

Before committing to 4 mm, I built the whole chair in 2 mm scrap aluminium. No laser cutter at the university would take metal, so I cut cardboard templates and did the aluminium by hand. Precision suffered a bit and 2 mm was far too thin, but it showed me how the assembly would go and where the weak points would be.

While building the model I also had to consider how to bend it and how to assemble it. It was really valuable building it just to get a sense of how it would look and feel, how it would react to the environment. A big takeaway was for the seat to be structural and tie the whole assembly together. Everything connects to the chair.

Hand-cut 2 mm aluminium parts leaning against a board, the leg profiles already bent. — Cut by hand from cardboard templates.

A 2 mm part being bent over the edge of a workbench, clamped as a jig. — Bent over the bench edge.

The 2 mm chair carried outdoors past a graffiti wall, held by one leg. — A visual test and a test of rigidity: did it read as a chair, and did it stand up.

Building the final prototype

I ordered the 4 mm laser-cut parts and wanted the parts CNC bent, but found no one near Vienna who could bend it. So I used the workshop roller and tried to get there by hand. Where a bend starts and stops is hard to control that way.

A laser-cut 4 mm part on the bench with a steel rule, a protractor and the paper pattern laid over it. — Marking out the bends.

A 4 mm aluminium sheet being formed between the rollers of a bending machine. — Rolling a leg by hand.

A hand holding a bent 4 mm part with the custom spacer fitted between the layers. — The spacer that saved the assembly.

The big bend on the seat beat me. The 4 mm sheet was too stiff for a roller that small, the radius came out too large, and every screw hole shifted.

I fixed it with a custom spacer that took up the misalignment and bridged the gap it left. It was a repair, but I have come round to it. The gap between the parts is now one of the better things about the chair.

The bent 4 mm parts standing on cardboard, part-way through assembly. — Assembly.

Colour against the construction

A deep blue-green, set against a construction that is otherwise very technical. The spray finish came out rough and uneven, which was disappointing after the work on the parts. The renders show how it is meant to look. I later repainted the chair grey with a better lacquer, which is the finish in the picture.

The chair in a spray booth after being coated deep blue-green. — In the spray booth.

The chair repainted grey, standing in the studio. — Repainted grey, with a better lacquer.

Five parts, one direction of bend

One backrest, one seat, two side legs and one front leg, all 4 mm aluminium, laser cut and bent. Every fold runs the same way. Nothing is pressed, nothing is double-curved, and there is no bracing hidden inside.

Material: 4 mm aluminium sheet
Parts: 5: backrest, seat, 2 × side, front
Forming: Laser cut, roller bent
Joining: Screws and spacers

Exploded view of the ALU Chair: seat panel, backrest, leg frames, screws and caps.

The ALU Chair in blue-green from three-quarter, front and side, rendered as intended.

Key learnings

The feedback afterwards was that more three-dimensional (stamping) geometry would have been structurally more efficient. That is true, and is exactly the constraint I set out to test. Still, my process might have been too rigid. I locked into one method and one visual language early which left little room for exploring other materials. I was also a bit afraid of going for stamping as it is pretty difficult to prototype.

I do think it was valuable to dive deep into one production method, and something interesting usually happens when you dive deep into a given process or material and try to push the limits. This project made me more comfortable with prototyping in general and just building and seeing where it leads.