Our pal Gavin Harper cooked up this great how-to on making a geodesic dome…
In this article, we are going to be looking at a simple lightweight bamboo geodesic dome structure that you can erect in your garden as a temporary shelter for leisure use. This structure is so lightweight, that you could even safely give it to your kids to put up in an hour.
Geodesic Domes are great futuristic looking structures that enclose a large amount of space for minimal materials. At the Centre for Alternative Technology www.cat.org.uk I have just finished my last module of an MSc. Architecture: Advanced Environmental & Energy Studies. www.cat.org.uk/msc. Our team, Joe Lee, Ian Dalgliesh and myself Gavin Harper had to make a kit of parts for another group to assemble our timber frame structure. We were investigating structures and for our design project decided to build a Geodesic Dome.If at this point you are confused about what a Geodesic Dome is, Wikipedia has a good article.
- Quantity of Bamboo Cane
- Polysulphide Adhesive
- Cable Ties
- Red Electrical Tape
- Blue Electrical Tape
- Cling Film / Shrink Wrap / Saran Wrap (Optional)
- Tin Foil / Aluminium Foil
This structure is scalable. We worked on a long strut length of four feet, we will need 35 of these. To identify them we wrapped them with a band of red electrical tape to aid assembly. We will refer to them as “Red Canes”. The short canes being three foot six were wrapped with blue electrical tape to identify them. You can make the structure bigger or smaller. The rough and ready math is that the short struts need to be around 11% shorter than the long struts.
The first steps are REALLY boring a repetitive – the sort of job you need to find a younger sibling to do Essentially we want to end up with 35 canes that are four foot in length, and 30 canes which are three foot six inches in length. Because this structure relies on all of its elements for strength, you want to find bamboo with at least a half inch diameter cross section. Discard lengths where the ends are split.
When cutting bamboo, you will need to use a fine sharp saw. We found that s jigsaw with a sharp blade made the process a lot less labour intensive that using hand tools.
Construct a jig this will allow you to measure and mark the canes with relative ease.
We are going to attach eyelets to the ends of the bamboo canes by screwing them into the hollow centre.
The polysulphide adhesive was the crucial addition made by Ian which makes the project work. As well as setting very strong in only a few minutes, the glue foams and expands to fill any gaps.
This is useful as Bamboo is a natural product, and as a result is of a variable cross-section. When trying to join eyelets, whilst some screw in strongly and provide a solid grip, others do not form a tight fit with the bamboo. In this instance the glue fills the gap.
Adhesives always stick much better the first time around. So glue the joint, allow the joint to set, then leave it to dry fully before trying to assemble the dome.
One all of the joints have dried, you should be left with 35 red canes and 30 blue canes with eyelets at either end – now we come to assembly.
Bamboo is naturally hollow. This makes it fairly easy to attach eyelets. However, one thing to be wary of is that there is a soft pith in the centre of the bamboo canes. If the glue sticks to the pith but not the bamboo cane itself, then the eyelet is liable to pull out. It will take the pith with it along with the solid glue. If this happens. Simply reglue the joint.
To avoid this happening, first using a drill or other implement, remove the pith so that the glue adheres to the hard outer cane.
When using canes that are eight foot long, there really is very little spare bamboo at the ends of the cane going to waste. For our whole dome, the image below shows how very little bamboo actually went in the bin – most of these small pieces were split bamboo anyway which was of poor quality.
There really is very little wastage.
Assembly really is a piece of cake – it is made even easier by the completely foolproof diagrams drawn by Joe Lee to whom I am truly grateful. The only problem is, as Douglas Adams famously said, the problem with trying to make something completely foolproof is that people underestimate the ingenuity of complete fools.
The image below illustrates the placement of red and blue canes. You need to remember that this is taken when looking from above, down onto the Geodesic Dome.
Diagram Showing The Location of Canes in the Finished Structure
The first thing to do is to lay out the outer circle of 10 red canes. Once you have done this, you will need to insert cable ties loosely through the hoops of the eyelets. This allows you to attach additional canes.
The First Step – Laying Down the Outside Ring Of Red Canes
Now you need to lay down the first course of struts which will form the first level of triangles. The struts are laid in a pattern that follows two red, two blue struts around the circle. Now link each strut to the others at the base and tighten the cable ties allowing a little movement for alignment.
The Second Step – Laying the First Course of Triangles
Now you need to attach the ring of blue triangles which sits atop of the first course of triangles. Because this level is elevated, you are probably better “cable tying as you go” rather than waiting for the next level of triangles. You should find that the triangles are able to all lean against each other and stand up supporting their own weight.
The Third Step – Attaching the Ring of Blue Triangles
Now we will attach the upper course of triangles. Think of this like a red star, with the spare blue struts completing “blue pentagons” at the base of the structure.
The Fourth Step – Attaching the Upper Course of Triangles
Now the dome should really start to take shape. You now want to attach a pentagon of red rods to the points of the star. At this point, you might want to start taking up the slack in all the cable ties in the structure to give it some rigidity.
The Fifth Step – Attaching the Upper Red Pentagon
Now the crowing glory – the upper Blue Roof Star. Take five rods, and anchor them loosely in the centre. Take the five arms of the star, attaching them to the nodes of the pentagon. When the arms of the star are all attached, tighten the cable tie in the centre.
The Sixth Step – Attaching the Roof Star
This provides a nice frame which is surprisingly strong and resilient. The beauty of Geodesic structures is that the provide a massively parallel amount of triangulation, meaning that when all members are in place, they form quite a strong rigid structure.
Optional – Cladding the Structure
After performing some destructive testing, we found that the “nodes” where the cable ties join five or six canes together were particularly vulnerable. In the event of one of these breaking, the rest of the structure rapidly deteriorated, however, in one individual cane breaks, or and individual cane-eyelet joint fails, the structure is particularly resilient.
- Gavin D. J. Harper Esq.