Step 1: Computer Aided Design
Since I wanted to order all the profile sections pre cut, I thought it would a good idea to draw the chair with a CAD program. I used a fairly simple 2D CAD program named QCAD for two reasons. It was freely downloadable and my computer lacks the processing power to handle 3D CAD effectively.
If you have access to AutoCAD, you could benefit from the plug-in from Bosch-Rexroth. If I have understood the information about the plugin correctly, it provides you with a catalogue of parts that you can copy and paste into your design. Later on, you can "punch a button" and print an order with a list of all your parts.
Even though I had to draw all the parts myself, cadding the design was very helpful.
Step 2: Double-Checking the Design
Before ordering all the parts from Bosch-Rexroth, I built myself a styrofoam scale model.
I wanted to see how the chair looked in 3D, but also double check that no parts were competing for the same piece of space-time real estate. 2D CAD may have its merits, but it doesn't help you discover such problems.
This model also provided me with a feel for the weak spots in the construction. I could push it here and there with my fingers, observing were it bent the most.
Step 3: Unpacking and Labelling
The whole "kit", weighing over 80kg!, came in two compact boxes.
When spread out on the living room floor, the components piled up quite impressively. In order to avoid silly mistakes, all parts were measured and marked.
Step 4: Bolting Everything Together
Eh, well, I am sorry. This "step" should be replaced with proper instructions, but I can offer two hints:
Always buy/use high quality tools.
Proof-read your Instructable title twice if you work late in the evening and use foreign words!
Over time, it has turned out that the belts are not held in place by the elegant scheme I use in the last picture of this instructable. They creep slowly, slowly out of the T-groove. Sadly enough, I've had to secure them with seams.