A “3V” geodesic or polyhedral dome is made of hexagons and pentagons, which means you will need 2 basic triangle shapes, called BAA and BCC. Start your project with a visit to desertdomes.com
, where you will find dome diagrams, dome formulas and an invaluable dome calculator. This Instructable is for a dome with a 7’ radius; this is a “5/8” 3V dome meaning taller vs flatter, over 8’ tall in the middle. The dome likes a flat surface to sit on making it ideal for the open desert playa, not so suitable for uneven terrain. The dome base isn't exactly flat, but close; the flexible nature of the coroplast bows and yields a little when you deploy it to make up for any uneven contact (Note: the prototype pictured here has a radius of 7.2’ but wasted more material from a 4x8 sheet. My next dome and this Instructable use the dimensions for an 84” radius - 7')
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.