Geodesic Dome Connector - Bogdan style

Inspired by Bogdan Isopescu's clever solution https://www.kickstarter.com/projects/25645348/geo-the-geodesic-dome-connector

I'm experimenting with printing the bottom part of the piece with flexible filament (TPU) and then print the upper part in non-flexible PLA.

To make the printer (Prusa i3 mk2s) pause at layer 6 (0,35 mm layer height) I'm adding the following post processing command (I'm using Simplify3D):

{REPLACE "\n; layer 6," "\n;*PAUSE*\nM83\nG1 E-1.000000 F6000\nG91\nG1 Z5.000\nG90\nG1 X10 Y10 F6000\nM84 E0\nM0\nM82\nG92 E0\n;layer 6,"} Fusion 360 link => https://a360.co/2InM4xV

How I Designed This

After a long cold winter spring finally arrived. To really test the connector to its limits I decided to go for a 3/4 dome v3 with 3.8 m diameter - the largest and most complex dome I've attempted so far.

http://acidome.ru/lab/calc/#Align_3/4_Piped_D42_3V_R1.8_beams_36x25

The struts are made from inexpensive 25x36 mm planks. With this connector struts don't need to be tapered, just cut straight at a 90-degree angle. So cutting up all the 210 struts was a pretty quick business after all.

This is one of my favorite building materials

Struts painted with an equal mixture of tar, linen oil, and turpentine. Smells as lovely as it's sticky.

I thought marking the struts was perhaps overdoing it but it turned out to be super helpful later when assembling the thing.

I had printed over a hundred connectors but that's not nearly enough for this dome so I had to print some more. I recently changed the PEI sheet on my printer and it was probably too smooth and clean because the flexible filament stuck to it so hard that I eventually ripped it. I had no spare PEI and the Prusa shop was out of stock. What a disaster! Without the PEI sheet, my printer was rendered unusable. While looking around in my workshop for possible solutions I found these metal bands with holes that happened to match the printed connector exactly. So I tried to cut pieces of metal bands and use them as a replacement for the printed connectors and it turned out to work quite ok. So the bottom part and the very top has printed connectors and the rest has metal ones. On the positive side, I can now compare how both types fare with time and weather.

Lots of connectors and this isn't even enough.

Disaster happened - I ripped the PEI

Desperation can be a source of innovation

3D printed connectors

Metal connectors

It took us about 3 days to put the dome together. It's hard work both physically and mentally. Sorting out which strut goes here and which goes there at the same time everything is on the verge of collapsing can be quite stressful. Having just two arms is sometimes not enough and the structure is quite flimsy until the last piece is fitted and the thing becomes one whole stiff thing. It's amazing to experience when it happens!

Half way there

Final pieces mounted in darkness

The morning after

A simple door makes the dome a bit more accessible

Covered in thin plastic

The cover is made of thin painter's cover plastic fastened with staples and tape and then shrunken tightly with a heat gun.

The story continues on https://twitter.com/hashtag/chilidome

Someone is now selling the #chilidome - lol ;-)

Inside the "Chilidome"

Thai chili - pretty hot (but far from the hottest ;-))

Mega hail!

Huge hail shredded the 0.03 mm thin plastic. Luckily the thin plastic is easily repaired with clear packaging tape. It might not look as nice at the end of the season as it did in the beginning, but it works.

Late autumn

End of season 1

The dome survived the 2018 season. At first glance, the 3D printed connectors seemed have fared pretty well. However, things progressed rather quickly when I began removing the plastic cover. In hindsight, I should have put up a camera to document what happened and how things escalated.

This is what happened: it turned out that some of the plastic connectors on the lower sections had broken and it was just the plastic cover that had been holding things together. I was optimistic though and thought I could replace the broken connectors with metal ones.

An interesting property with the dome construction is that it is only rigid when everything is connected, so now the dome started to behave rather flimsily and more connectors started to break. It came to a point when I realized I could not fix it, so I decided to dismantle the whole thing and rebuild it properly next season.

Is this idea a failure? I guess it depends how you look upon it. The 3D printed connectors were definitely too weak for a 3/4 sphere of this size. I think they can be adequate for a smaller dome, but then again the metal connectors are cheaper, easier to produce, and stronger.

Bottom and midsection was where the connectors broke

Things falling apart

Back to square one ;-)

Category: DIY