Step 1: Computer Aided Design
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
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
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
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.