Tensegrity Coffee Table
Introduction: Tensegrity Coffee Table
A year ago I made a living room furniture for a friend of mine with an industrial style; since I am an engineer I wanted to add structural concepts to the design and therefore I made it by inserting tensegrity elements.
The top was made with the "shou sugi ban" technique which is very nice together with the steel frame. Another friend of mine saw this first job and he was amazed and asked for one for himself; I also offered him some finishing variations but he was in love with what I had already done and he wanted it identical.
Step 1: SAFETY FIRST
Safety must come first! For this project I mainly used these power tools:
Welding machine
Angle grinder
Drill, better a drill press
Circular saw
Each of them needs a specific safety equipment that must be worn correctly according to what is written in the user manuals.
Step 2: BOM
To make this 80x50xh.60cm table I used:
* about 7m of 30x2mm square box
* about 2.6m of 30x3mm plate
* 4 feet
* 4 cables of 65cm each
* 4 cables clamps (not needed if you use brake cables with already mounted end caps)
* 4 M10x40 bolts with washer and nut
* wood screw
* 4 L to fix the tabletop
* tabletop
I have spent about 40 €. For the tabletop I used leftover strips from my pitch pine parquet as it has a really beautiful grain; other wood species or a laminated glass sheet can also be used as desired.
Step 3: WHAT IS TENSEGRITY
The word tensegrity derives from "tensional integrity" and refers to structures whose stability is guaranteed by the coupling:
- tense elements, generally composed of cables;
- compressed elements, more squat, with adequate flexural stiffness.
Tensegrity structures are based on the combination of a few simple design patterns:
* members loaded in either pure compression or pure tension, which means that the structure will only fail if the cables yield or the rods buckle. This enables the material properties and cross-sectional geometry of each member to be optimized to the particular load it carries.
* preload or tensional prestress allows cables to always be in tension, to maintain structural integrity.
* mechanical stability, which allows the members to remain in tension/compression as stress on the structure increases. The structure also becomes stiffer as cable tension increases.
see https://en.wikipedia.org/wiki/Tensegrity
Step 4: CONCEPT
The concept behind this piece of furniture is simple: the upper frame is hung from the lower one through a chain and the 4 lateral cables have the purpose of stabilizing the structure, which otherwise would be in a situation of incipient motion.
The two frames are perfectly identical in shape and size, the only variations are represented: by the feet present in the lower frame only and by the tensioning devices in the upper frame only, in which they will be hardly visible as they are hidden by the wooden top. The frames are made up of a square box of 30mm and 2mm thickness, shaped as per the attached sketch.
The 4 side tie rods are ø1.5mm bicycle brake cables, guaranteed for a load of 40kg each and will need to be pretensioned for about 20kg. 787
To make sure that all cables have the same voltage just pinch the cable and listen to the note produced, you can also help yourself with an app on your mobile phone, which indicates the frequency (Hz) of vibration. For your curiosity you can also evaluate the traction on the cable: https://www.spaceagecontrol.com/calcfunm.htm?MA%5...
The central chain, when the cabinet is unloaded, will therefore be subjected to a traction of 80kg (20kg x4 cables) and therefore cannot be identical to the side tie rods. When the piece of furniture is loaded, the traction on the central chain remains unchanged while that on the tie rods decreases.
Step 5: SHOU SUGI BAN
The <PERSON> technique consists in carbonizing the surface of the wood with a flame. Carbonization decreases the moisture contained between the fibers and closes the pores of the wood, making the surface compact and hard. At this point the boards are much better than normal resistant to sources of heat, water and humidity, parasites and insects and UV rays.
This technique was born in Japan and has been widespread on the island since ancient times but has been supplanted by the use of chemical coatings, dyes, paints. Recently this technique has begun to spread worldwide, also thanks to design choices that involve giving color to the tables and at the same time maintaining the contrast with the burnt veins, which remain black. 959