Materials Arrive

The Hubs

The hub kit arrived after a few days and was roughly the volume of 2 shoeboxes.

This is the 3V frequency option and can be used for all sizes....ie angles stay the same only the appropriate stick lengths change. (see calculator )

Core Hub Module llooks like this. (smaller than you'd think)

Ball joint clips into the hexagonal / pentagonal connector and secured by screw, washer and wing nut combo. The ball joint is attached to your stick of choice via a screw that extends 3.2cm into same to end up coincedent with the flat of the ball joint arm. Takes a little force to clip the ball into the socket and a little play in the angle of the ball wrt the joint but generally feels good. 

61 hubs in all for this dome and 360 ball joints to connect everything up......A lotta lotta work ...so need to get it right first time. (some trials required re ball to stick connectivity).

The Poles

The bamboo poles followed a few days later. Ordering is done in 4m lengths which you can have delivered as 4 x 1m , 2 x 2m or a single 4m pole options. The 2 x 2m option had half the carriage cost of approx 60€ for the 50 (4m= 100 x 2m poles I ordered to construct my 5.2m diameter dome.

The poles arrived in 2 rolls with the ends protected by tightly wrapped polythene. There is considerable variation in the 3 cm diameter but the supplier advised about this due to natural tapering of plant and sorting tolerances. For our purpose (as described in the guidelines) a maximum diameter of 3.2cm is fine with some machined tapering rerquired above that value. 

The total weight of the 100 x 2 metre long poles came in at 38Kg split between the 2 rolls ie easily moved with a little effort. 

On closer inspection there was a greater variation in diameter than I had expected from the supplier. I decided to measure all of the diameters at both ends to see how I can accomodate the variation best in the geodome build and also to give feedback to the supplier, UK BAMBOO SUPPLIES LTD.

The above graph shows the variation in diameter of the wider end of each of the 100 poles. As you can see only 3 fall in the expected target range of 30-35mm.

Looking at the tapered end the situation is of course worse again.

Approx 40% of the poles have a diameter of 20mm or less. A taper is to be expected ...and quite a large taper on occasions, but given the average starting diameter is approx 6mm less than expected there may be some penalty to pay in the robustness of the erected structure. Having said that , bamboo is inherently very strong and I ordered the 30-35mm diameter poles purely on the basis that this was the largest diamater the hubs could easily accomodate. It is unlikely but not impossible that these narrower diameters may be a liability down the line, but hopefully keeping these poles towards the top of the dome will be a successful strategy.

Inner Diameter of Poles

This is a bigger issue (as of just now). The inner diamater ....ie the ends we need to plug in order to accomodate the ball joint screw (shown above) varies like crazy due to both the outside diameter (as above)  and the sidewall thickness...which can be the full diameter (ie solid) or more typically between 2 to 7mm. In order to accomodate this variation with softwood dowels (original idea) I need dowels of diameter 7 to 23mm ideally in 1mm steps.

Alternatives might be plastic rawl plugs or epoxy resin .....Need to contemplate and run a trial or two to determine which is robust enough , cheap enough and reproducible.

Just saw this on the web....Maybe its the way to go .....Buy a few dowel diameters and then customise them as shown below and described more fully here.

Insert dowel that is slightly too large into drill bit and with a very rough sand paper ....take the diameter down to a nice snug fit. Looks good to me.