This instructable is going to take you through my process of design and development and give you all the information you need so you can build a 4m diameter geodome kit for under £50. I am also going to go in to some key decision points and ideas for keeping the cost down and making this accessible for every one, i will also put in some options that you might like to consider to make this work for you. All the materials I have used and tools should be easily available free or cost effective.
Why did i build this?
I have been researching geodomes for a while and just love the concept and the aesthetic that they have. I wanted to create a geodome kit, that my Cubs and Scouts could build on summer camp and possibly sleep in.
Key cost drivers:
keeping the cost down keeps thing accessible and enables plenty of prototyping. key cost drivers were price per meter for the spares and price per fixing for the hubs
Domes can be complicated to design and build but the methods I have developed eliminate most of that.
after a quick bit on what is a dome and what type to select, im going to jump straight into the fun bit, the building and will add extra stuff at the end
Step 1: What Is a Geodesic Dome (geodome)?
There is tonns of great technical material on the web, have a look at the link below or google it. In essence they are a dome made out of a number hexagons and pentagons each divided into triangles (like a football (soccer) made of leather patches). Structurally they are very strong and can take huge amount of loading from wind and snow. One key structural aspect is large areas can be covered with relatively short lengths of material without internal supports.
Designing them can get quite technical but the methods i use eliminate a lot of that. Just one technical bit to remember is the dome frequency (V) V1 (simplest) V6 complicated. The dome I am going to build is a V2 and will mention V1 and V3 (more on that later)
first choice v1 v2 v3
Comparison for a 4m diameter dome
max length of a strut (m) 2.1 1.24 0.83
total length of strut (m) 53 82 131
total number of hubs 11 26 61
V1: requires long struts so they need to be fairly rigid
V3: required loads more hubs and material so although stronger, it is going to cost more almost double for the structure
optimum choice for a 4m diameter dome i think is a V2
Step 2: Materials and Tools
Spars: 65 spars total length 82m (bundle of 1.25m x 25 = £4 x 4 lots running total =£16)
Price per meter and strength was important. During a recent trip to Nepal we built quite a lot of stuff out of bamboo and it is both strong cheap and light.
Bamboo Diameter: Initially i thought i would need about 25-30 mm but when looking in the shops i went for about 12mm. Turns out this has loads of benefits
Hubs: (this bit that joins all the spars)
I use a combination of 2 options both work fine
Cheapest - string or cable ties ( i used this a lot for testing and for full building)
Nuts, bolts and washers ( to date I haven't built the whole dome with nuts and bolts but the tests look really good and next time I build it I will be using nuts and bolts instead of string) 2*25 *£2.5 = £5 running total £21
As this was a kit for my Scouts and not a permanent structure needed a system that they could build easily and consistently. After some prototyping i found screwing metal eylets into the end of each bamboo meant they could then tie them together easily with a simple double knot.
65 spars in total = 130 eyelets, 100,4mm bag = £5 x 2 lots (running total £31)
One tin of two pack wood filler (had that in the cubourd (lets say £5) you don't need much (running total £36)
all other bits (running total £49) ; )
12mm bamboo x 65 * (longest length) (plus some wast)
26 nuts and bolts (m6 40mm)
2pac wood filler
2 different colors of tape
Drill (3mm) - drill out the bamboo
saw - cut the bamboo to length
knife - cut string
Step 3: Cut the Spars to Length
I used the V2 dome calculator here:
so the two lengths i need are:
A 30 x 1.093m (Red)
B 35 x 1.236m (Blue)
I adjusted the length slightly to take into the consideration the eyelet not sure how cruical this is but the closer you can get to the actual lengths the better.
Bamboo is not standard so has some natural variants it also has nodes these are your friend if you can get a node near the end of your strut you can screw the eye into it and it wont split and is really strong. I wrapped duct tape around where the cut would be to limit any splintering when i cut them
I lined the nodes up where i could at least on one end. It takes a bit of time but is worth it.
I bundled them up and cut them on the chop saw i also used a hack saw for some of them it actually give a better finish but might take a little longer.
You should now have two bundles of two different lengths
Step 4: Eylets
The center of bamboo can have a very soft center. To clean this out i used a screw just pushed it in and out a bit it worked really well.
Some end sections have a very thick wall and tight hole (smaller then 3mm) some have a wide hole (bigger then 4mm) some end sections might have a knot near them
Drill out all the ends that have a tight hole or a knot with a 3mm drill and screw an eye in them
You will end up with bamboo that you cant screw an eye into as the hole is to big. This is where the filler comes in.
Mix up a small amount (it goes off quickly) and try and force some in the end of the bamboo i used a plastic credit card and that worked fine, I also spread a bit on the screw thread of the eyelet. While still wet screw an eyelet into the filler and pack some more in if you can.
Critical - make sure the eyelets on each end of the bamboo roughly line up
Eyelet O======Bamboo=========O eyelet both lined up (not twisted relative to each other)
At the end of this you should have two different length bundles of bamboo with eyelets in each end
Step 5: Marking Up
As this is a kit you want to make it a little bit easy to assemble and sort out
Rap red electrical tape around the A (short) struts
Rap blue electrical tape around the B (long) struts
You could also use paint or nothing if you want to make it hard to assemble later
Step 6: Build Your Dome
Building I am sure you can just work it out from the picture how to assemble it. My garden is a little small for it so i took it to the beach with my mate and his kids (5-7) the 5 year old cut the string and lifted up sections and the 7 year old tied the knots with a bit of help at first and none needed by the end.
It was also blowing hard and the dome (although not covered) stood up fine.
Hub Connection Method:
2. Nuts bolts and washers (hint: don't tighten the nuts up leave them as loss as you can they need some wiggle room, tighten them up at the end if needed)
Top Down Building method:
Build the top pentagon first and work your way down. This works well for light domes and when you have little people helping who cant reach 2m
- Lay out the top pentagon 5 red 5 blue
- Lay out the second layer in the order BRB * 5
- connect the centre 5 R spars
- Work your way around the next ring connecting the spars together
- Lay out a complete ring of red spars
- Lay out the next layer of spars in the order BB RR (linking blues to the layer above and the same with reds)
- Connect the spars together
- Lay out the final ring or blue spars
- Connect the spars together
- Dome built
Bottom up build method:
lay the bottom ring then work up great for big heavy domes.
There are some great instructions for the bottom up approach here but using a different hub method
Step 7: Covering
You can cover it in what ever you want, if you have a youth club they could make and decorate a panel each out of cardboard or fabric if you are not using this outside, there are loads of options including:
Plastic sheet/ bin bags
The options are endless and depend what you want to do
I managed to get hold of an old fly sheet for a broken tipi and at the moment that works for me although I might try and refine the shape at some future point (any one a wiz on a sewing machine let me know) i just tucked it under and tied a ring of cord through the peg down points and pulled it all tight. Then weighed it down with some water bags just to stop it moving in the wind.
Step 8: Creating a Door
To create a larger door I disconnect one of the hubs and moved some of the spars around (see highlighted picture) I tried to maintain the triangle where I could and used some tape and sting to tie it into place, it didn't need any extra spars. Just have a play, i'm sure it will work for you.
Step 9: Lessons Learnt and Other Options
No more nails doesn't work as the glue shrinks when it dries, 2 pac glue or filler works better
Don't use week string as it will need to take a bit of load
Plastic bottles hubs:
After my initial build I really wanted to build a V3 but that meant more hubs and more spars, so back to the drawing board. Then one night I woke up with the idea to use plastic bottles. I actual sat up in bed drew it and went back to sleep. The next day i knocked up the prototype you can see. it is so simple. cut the top off a bottle and remove the tamper ring drill 5 or 6 holes then cut down through the thread to the holes. Use a normal screw in the end of the bamboo with or with out a washer. Slot them into the holes then screw the cap back on. It makes a proper solid hub.
nearly all bottles seem to work but I like the one with a wide neck and there is a load of plastic in them so they are tough.
The hubs price just dropped to close to 0, if you drink a lot of squash. The spar price has come down as now you just need normal screws and it will make it easier to screw into a node and the screws are longer than the eyelets are.
I cant wait to build a V3 with this new hub design and I will post it when I do. If any one works for Robinsons and want to ship me 61 bottles of squash I might even get it built for scout camp. I only like peach flavour though!
Where to buy stuff
I brought a lot of the hardware from Stax but ebay looks good for eyelets and Amazon for bamboo.
Step 10: Thanks for Reading
I hope you enjoyed this and you get a chance to build your own
If you have any questions or are struggling to get parts please ask I am not a shop but could potentially put a few kits together with all the hardware if any one is interested.
I'm going to enter this in the outdoor competition so if you like it please vote and if I win i'm sure my Scouts will love the tent prize too.