It takes 105 triangles to make the particular dome shape I wanted (called a 3V), which could be a time-burner to assemble. The Folding Geodesic Dome simplifies things with tape hinges that pre-connect many of the triangles into 16 segments, each of which can fold into a small stack and connects to its neighbors via tabs and clips. The more hinges used the less time spent connecting triangles in the field. The dome goes up with 2 people in 2 hours or less. Takedown time is 30 minutes.
There are great Instructables for light domes made from coroplast or cardboard which negate the need for a support frame. This dome was made with an eye for economy, using 20 surplus 4’x8’ 4mm coroplast political campain signs found on Craigslist for $100. The panels can be made from any stiff material (cardboard, coroplast, thin plywood, plexiglass) that is rigid enough to resist bowing.
This project was made possible by the resources at desertdomes.com including their dome calculator, dome formulas and the dome diagram that I use in this Instructable. (If you build a dome, please donate to desertdomes.com as I did.)
This dome is a light-duty ‘backyard’ dome, done as a proof-of-concept; it isnt’t waterproof or windproof enough for open country yet. My next version will utilize a combination of thin plywood for the hexagons and coroplast for the pentagons (to let light in) and will address weatherproofing. This project was a runner-up in the ShopBot Contest - most exciting! Thanks to everyone who took the time to vote.
Step 1: Design
The dome is composed of 3 basic folding segments: a pentagon (5 triangles), a hexagon (6 triangles) and a “hexagon plus 3” (9 triangles for the base row ). Each segment unfolds and is clipped into a convex shape with binder clips or a clamp made from pvc pipe.
To calculate the dimensions of the 2 triangles (BAA and BCC), use the desertdomes.com dome calculator and enter the dome radius in inches to get get the lengths of the A, B and C triangle sides.
For the radius of 84” (7 feet) we get
A= 29.284” (roughly 29 1/8”)
B= 33.898” (roughly 33 7/8”)
C= 34.642” (roughly 34 5/8”)
I used those numbers to calculate:
Height of BAA = 23.881” (roughly 23 7/8”)
Height of BCC= 30.213” (roughly 30 1/4”)
.5xB = 16.949” (roughly 16 15/16”, for the midpoint of the B edge)
For the 3V, there are 30 “BAA” triangles (to make 6 pentagons) and 75 “BCC” triangles (to make 10 hexagons and 5 semi-hexagons). 1” wide tabs are placed along B edges to connect segments together, and on some of the C and A sections too. The triangles along the base of the dome have 4” tabs with holes for the anchor stakes. Edges that don’t have tabs will have tape hinges that connect to their neighbors. I’ve mapped out where the tabs need to be for every triangle needed in the dome, adding up to 12 different shapes you’ll cut - download the pdf Cutlist for shapes and quantities.