Slow, flexible & cheap

Despite the superabundance of DIY tools that can be found in books and on the internet, very few designs approach dome building from a non-shelter perspective.

Rightly so, the common thought is to design a connector that’s as rigid as possible, to prevent any mechanical wiggling that could occur. While rigid connectors are great for building a load-bearing spaceframe, they’re not so well suited for the type of dome building I was interested in.

What follows is the story of how it took two degrees in design and six years of prototyping for me to create the final form: a rubber hexagon with holes in it. It’s been a slow, arduous process. I’ve made a lot of hilarious and expensive mistakes along the way. Let me tell you.

3d-printing

I started by trying to 3d print dome connectors on my Makerbot (an early batch 5 Cupcake, #96). Working from an open-source design I found on Thingiverse, I invested the weeks-worth of time it took to modify the design and successfully print the 26 connectors I needed to make a 2V icosahedron dome.

 I had my mind set on making something bigger. While I could rapidly design and prototype with my 3d printer, going into production mode meant I had to stop my research & design process and tend to a finicky robot that needed constant attention.

So, rather than trying to print things myself, I experimented with crowdsourcing the printing of the connectors I needed for my next dome. The following was sent to all the 3d printing mailing lists I could find:

 Within two weeks I had all the parts I needed, printed by makers from all over the world. I invited over my friends Ezra and Andrew and we put it together in the backyard. It was awesome! Big enough to get inside, so naturally we did.

 This design had holes printed that would hold the strut at a precise angle. In order to make the dome self support, all the struts had to be the exact length and the structure built on a surface that’s perfectly flat (that’s why you see the wood planks in the picture above).

Wondering what would happen if the connectors could be flexible rather than rigid, I found and modified a 3d-printable ball joint connector on thingiverse to make the 5 and 6-way connectors required to make an icosahedron dome. This required a great deal of mechanical precision, and after a lot of calibration I was able to get my shaky Makerbot to produce a usable ball joint.

Despite each connector taking a good 6 hours to print, the design elegantly allowed each strut to self-adjust to the right position. There was no requirement to build it on a flat surface, and the flexible nature of the connector was easier for groups of people to build the structure.

 With the feeling I was onto something, I launched and successfully funded a Kickstarter project that delivered 3d-printed domes. With the help of my friend Mark Cohen from Brooklyn, NY, we printed over 1000 individual components in a couple of weeks.

 It was kind of a ridiculous thing to do, but we learned from this experience how boring production-level work with a desktop 3d printer is. The same object, over and over until the machine eventually breaks and hours worth of printing time is wasted. An obvious way to scale is to just injection mold it, but this design wasn’t ready for that. 3d printing is cheap, but slow. Maybe there was another way?

Tubes

For the Kickstarter project, I offered a cheaper alternative to the 3d printed design out of the prediction that folks would be more likely to buy a cheaper dome kit than a more expensive 3d printed dome kit. This prediction proved correct: we sold only 3 of the expensive 3d-printed kits compared to 27 of the cheaper design.

This alternative design was cheap and dirty, based off of something I saw in Domebook 1. Get a tube, cut it into lengths, put a bolt through the middle to hold it together, then stuff a dowel in the end. Crude but effective, it worked fairly well with flexible PVC tubing. Further iteration revealed an even lazier alternative: why drill holes when a zip tie will do?