written by Rene K. Mueller, Copyright (c) 2007, last updated Tue, November 4, 2008
As I proceed I will update the diary. Most up-to-date entry at top, first and oldest entry at the bottom respectively last page.
Bamboo / Conduit Combo Options
It has been almost a year since I pondered on the connectors for bamboo, because it seems it wasn't that easy to find something suitable.
At Bamboocraft.net has been a discussion with different approaches, yet, none really is convincing.
Discussing with a friend of mine, who is a locksmith, brought up this design as the illustration shows, using a special foaming glue.
The glue, named "Fermacell 59010", is slightly foaming or expanding and seals the 1-2mm gap seamlessly - as a few tests have shown:
Bamboo with steel pipe
Bamboo with steel pipe (close up)
One bamboo I cleared using a cutter to remove the glue and see small bubbles, whereas the other the overflowing glue remained as comparison.
For the first tests we dented the steel pipe, and in one case too much where you see the bamboo split - which should be avoided.
- Hubless: the screw could be removed, yet, then the static would solely rely on the glue, which could get brittle with the time, and a big surprise happen - so rather use a screw to fixate pipe and bamboo and have the glue as soft junction between two different materials.
- Hubdisk: the issue with this option is, that it can only used for large and fine-grided (high frequency) domes, as the angle how the struts reach the hub has to be small enough so it can be provided by the hole/screw itself, and not via the disk itself.
Bamboo / Conduit Combo
I hope to keep the light bamboo as struts, but find more stable or rigid connectors. The idea of making 92 joints or hubs could be also considered, yet, bamboo has a range of diameter, from 10-18mm approximately.
One idea is to use two kinds of metal tubes like electric conduits of 8mm and 10mm diameter, and either drill 8 and 10mm holes into the bamboo, and glue it into and stabilize it with a screw. For the few struts with less than 10mm using the 10mm conduit and move it over the bamboo.
And then squeezing the end of the conduit and drill the 4mm hole for connecting the struts then.
Will make a test of an A/B-pentagon to see who long the conduit requires to be, and also measure all struts diameter to see how much material of 8 / 10mm conduits I require.
Update 2008/04/07: to use the pipe within the bamboo poses a slight risk of breaking the bamboo, as the inside of the bamboo is soft and rather weak: you can break the bamboo easier from within than from the outside; so it rather suitable to use the pipe surrounding the bamboo instead.
I stayed two nights in the dome, actually a wonderful experience with so much space, the spherical space makes an alike sacred impression as the tipi does, an cathedral like awe I've got.
I gonna miss the dome, and will work for a stiffer but still lightweight solution using bamboo - as I like to avoid steel pipes which would make the frame too heavy and too hard to pitch up without additional tools, not to mention the inability to lift it up and move around when erected.
The dome I took down by just unscrewing 5 or 6 connectors, and took it away like a collar, and folded it in itself as far possible - and later unscrewed all connectors on the side.
So I'm back in the yurt
With the current setup with soft-pipe as connectors the skeleton is too weak, and the sun heat softens the pipe further - so much that tying the rain cover to the ground pushes the top down - so I likely will take the dome down much sooner.
I definitely require to find a better connector for the bamboo, the softpipe might only work with smaller domes and average temperatures.
Things learned with this test pitch-up:
- the higher the frequency (e.g. 4V) the more precise and less threshold allowed, e.g. soft-pipe connector might work much better with 3V and 2V icosahedron-based domes.
- connector with PE is stiff and might work at lower temperature (<20°C), but when 40°C gets very soft
- more "weight" due to fixating the rain cover (pulling down with cords)
- moving the dome requires stiff baseline, at least 3 people to move (at 6.4m diameter)
- the rain cover and maybe even the interior cover could be simply circular, and left over due the spherical wall can be done via folding
CONBAM.de , german bamboo expert, has special connectors for more stable and large domes.
Preliminary Dome Setup (no ropes and fixations)
Today I switched from the yurt
to the dome - I took down the yurt and moved the skeleton of the dome on the same interior (both yurt and dome having ~ 6.4m diameter), finally we were 4 people moving, not neccessarly because it was heavy but clumsy to move.
Yurt & Dome
Yurt taken down, floor & interior left
Dome skeleton moved on floor & interior (me inside)
Dome skeleton moved on floor & interior
Preliminary dome setup (no robes & fixation, no door yet)
It took me a couple of days to erect the dome, usually it's a matter of an afternoon (4-5 hours) but it was so hot the last days I worked only early morning and evening before sunset.
We had also some rain, which wasn't so good for the fully exposed skeleton - anyway.
I also use a skylight frame so I could reuse the skylight from the yurt.
Finally, before I actually decided to switch I put over the rain cover of the yurt on the dome.
Dome skeleton moved on floor & interior (me inside)
It took 4 people to move the skeleton as the base tended to fold inside, and 3 people might have worked too with some skills but finally with 4 people we did it. The skeleton itself is rather light, apprx. 40kg I think total.
Once we had it over the existing floor and interior and moved it over the shelves, I had to move some interior further into the center, 10-20cm apprx., due the spherical walls.
Interior Cover & Rain Cover
Since I use the yurt covers (interior & rain) I had to use a cord which I tied on the height of 1.50m apprx. which is also the center of the A-pentagon - on that cord I tied the interior cotton, as first layer from outside. As next I added the yurt rain wall, also tied on the same cord - and finally put on the roof interior cotton, and then the roof rain cover from the yurt.
The skeleton with bamboo is strong, yet, the soft pipe junction are weak and soft, too soft. I don't expect it withhold a storm and make a tend (push a junction inside). The cable binders aren't that strong either, and while moving one teared apart, so I might have to use 2nd cable binder for all endings, at least on the west side where storms usually come from.
I was aware that the bamboo/soft-pipe combo was only suitable for a lightweight setup, rain cover and cotton interior I reused from the yurt setup, and now realize I won't able to add another layer unless I would choose another strut endings other than soft pipe.
The reason I use soft pipe was I could use them to various diameter as the bamboo came, 15-18mm - so I'm looking for other options.
Anyway, I'm expecting to stay a couple of weeks inside the dome, but as far I can see won't last longer and then switch back the yurt.
The next things to do:
- fixate the rain covers
- add 1.7m height door (I already did for a yurt)
So, finally again raising the dome, and checking if I can use part of the yurt setup, such as a skylight (octagon and a bit smaller than the top 'A'-pentagon) and this allows me as a first step to reuse the inner cotton cover (roof & wall) as well rain cover (roof & wall) of the yurt.
If all does well, I will switch the yurt for the dome sometime this weekend.
I noticed moving the dome is problematic due the base not being stable when it's not pushed on the ground, it bends inside and the entire dome looses its form - so I will stiffen the bottom connectors so the circular base is kept in shape so 3 person can lift it to the existing floor where my yurt sits on now.
Today I coated the 250 struts with white semi-transparent paint, so the bamboo struts are brigther and don't heat up so much anymore in the sun and reduce the risk of splits.
I'm also about to finalize the connector reinforcement construction and updated the previous illustration with the new design. Next days I will make a few tests with the construction, and if the weather allows it raise the dome within the next week.
Existing Connector (Closeup)
As I discovered with the first dome skeleton erection that my LDPE do good with bending, but a bit too much of elasticity for pushing, which allows then to dent the construction with little effort (apprx. 10-20N push ~ 1-2kg) direct on the connector (whereas area push withstands far more force, not yet measured), with this extension as illustrated I add a wooden construction, a wooden star to limit the LDPE elasticity for pushing force(s) only.
The wooden star would be composed by:
- center hub: 30mm diameter, 10-15mm long hardwood
- spike: 8-10mm diameter/width, 15mm long hardwood or softwood
Since the struts are slightly bent, apprx. 8-9°, I leave 2mm as spacing, but final length of the spike will be measured on the erected dome again.
Total 91 connectors, where as the bottom 20 connectors (4-way) I wouldn't enforce:
- 6x 5-way (connecting A's)
- 65 6-way
- total 71 connectors
Total requirement of wood:
- 71x 15mm = 1.065m x 30mm diameter hardwood
- 6x5 + 65x6 = 410 x 15mm = 6.150m x 10mm diameter/width hard- or softwood
So, this is the plan for reinforcing the LDPE connector so far, I will of course think it over again and make small tests, e.g. the 8mm spike is small and some will enter the hollow bamboo, so maybe a small ending of larger diameter is required.
The connector could be also stronger if I wouldn't have left 27.5mm but less, maybe 15mm could work too, or a whole pipe not a half but this would require a single diameter strut and with bamboo this is not possible - so it's likely worth to reinforce and find a strong connector solution in order to build the skeleton with lightweight but strong and rather cheap priced bamboo sticks.
Since we expect rain and snow the next days, so I already took the dome skeleton down, took me roughly 2 hours - I also wasn't able to take down the dome the way I planned before, I realized to keep some of the structure intact was too complicate (e.g. keep A-D combo together), so I finally disassembled the entire structure to each single strut.
But before that I measured the dome:
- diameter: 6.30m to 6.48m; best is to draw a circle like when pitching a yurt, to fit the bottom level (D) on that circle, actually the connectors
- door option I discovered a better way than thought before: taking the E triangle, and make a rectangular door, 1.70m high and 1m wide, 5 struts removed, none cut or so
4V Construction Map
I decided today to raise the skeleton of the 6.33m 4V geodesic dome I did - so far Roger and Gabriella joined me, two who discovered my web-site and approached me with their own plans to live in domes.
Pitching the Skeleton
I decided to build top to bottom, means, level by level until the bottom is reached - since the entire skeleton is apprx. 40kg it was easy to lift it for the last bottom level.
The construction map on the right helped me to lay out the struts on the ground and level by level attach them and screw them together.
Roger helped me and it took us about 4 hours.
Preparing Pitching 4V Geodesic Dome (2)
Pitching 4V Geodesic Dome, 1st & 2nd Level (2)
Pitching 4V Geodesic Dome, 3rd Level (2)
Pitching 4V Geodesic Dome, 4th Level (3)
Pitching 4V Geodesic Dome, 5th Level (1)
4V Geodesic Dome Finished (1-6 level)
4V Geodesic Dome (6.33m) (1)
4V Geodesic Dome (6.33m) (3)
4V Geodesic Dome (6.33m) (4)
4V Geodesic Dome (6.33m) (5)
4V Geodesic Dome (6.33m) (6)
4V Geodesic Dome (6.33m) (7)
4V Geodesic Dome (6.33m) (8)
4V Geodesic Dome (6.33m) (Closeup 1)
4V Geodesic Dome (6.33m) (Closeup 2)
4V Geodesic Dome (6.33m) (10)
4V Geodesic Dome (6.33m) (15)
First conclusions & experiences:
- the LDPE pipe is flexible as expected but it allows to push the 5xA into the dome with little force - so it's not suitable for whole year application (e.g. snow on the roof) but only for spring to fall, so I'm not sure to reuse the yurt thermal insulation due its weight, I may give a try. A storm may make a dent into the structure, but unlikely make serious damage
- for a full year applicable bamboo based geodesic dome a different connector approach is required, one which cannot be dented
After working a lot on geodesic polyhedra the last two or even three weeks, and finding out why my L3 variant of the Icosahedron didn't provide the same strut lengths as those from B. Fuller (via DesertDomes.com )
I realized that while doing the L3 from the L2 (geodesize an already geodesized L2/2V) that the strut lengths had less variance.
- L3: 5 strut lengths, 17% variance
- 4V: 6 strut lengths, 28% variance
I summed up 1/1000th or 0.1% variance of length to the same strut, so I ended up with 5 strut lengths, the 4V could also have 5 strut as two strut lengths are so close but not as close as the L3.
But the variance difference is quite obvious and it would mean to have more alike triangles and probably also less waste (which I have to proof first).
Anyway, I already have cut and assembled all struts, I won't change it - but for another and future version I might prefer the L3 over the 4V variant.
Ln vs nV:
- Ln creates more alike struts - less variance, and it seems less strut lengths even
- nV provides more fine tuned triangulation, e.g. 3V or 5V, whereas L1 = 1V, L2 = 2V, but L3 ~ 4V, L4 ~ 8V etc.
Pitching the Dome
The last days were very sunny, but night and day temperature difference up to 15°C which I like to avoid to expose the bamboo struts - as I would expect them to crack more likely.
So I likely wait a few more weeks before I make the first pitching of the dome skeleton.
Next Page >>
- Page 1: The Numbers, The Details, Connector, Skylight, Door, Cover, Interior, 2nd Floor
- Page 2: The Diary, 7. 4. 2008: Other Connector Ideas, 6. 5. 2007: New Connector Ideas, 1. 5. 2007: Dome Taken Down Again ...
- Page 3: 20. 2. 2007: Planning Pitch Up, Take Down & Storage, 19. 2. 2007: Completed Struts, 11. 2. 2007: Adding Connectors ...
- Page 4: 18. 1. 2007: Starting with Planning, 10. 9. 2005: Building 4V 4/8 Model, 30. 8. 2005: Building 2V & 3V Model ...