Colin sent me a very interesting e-mail with information about strut angles for a 3v geodesic dome, I''ve uploaded it here because it has some very useful information that gives some insite into 3v dome angles:

Hi Paul,
I had some spare time today so i thought i`d take a look at the angles for a 3v hub/strut geodesic with rebates/slots for fitting triangular panels.

I`ve attached a pic which shows the details (you`ll have to excuse the top quality pc artwork..i prefer to use good old fashioned paper and pencil)

I haven`t tested it but it should be quite accurate. It wouldn`t take much to knock up a full hex or pent panel to test the theory.

The slots should be easy to cut on a table saw with a tiltable table and adjustable cut height. I doubt anyone can cut the angles to 2 decimal places but the closer the better.
Ideally everything should be within a mm or so.

The hubs pose some problems but if the triangle panels had the corners nipped off (flat) I guess it wouldn`t be too difficult to get a reasonable seal against the hub using some kind of goop ;)
It may even be possible to route a slot around the (wooden?) hub itself to locate the panel tips...something else to look into perhaps.

Making the faces of the hubs the same width as the timber used for the struts would probably be best the best bet but entails different sizes for both pent and hexagon hubs.
The downside is that it deoesn`t leave much hub area for fixing to the strut.

All in all, it could be a daunting project for an experienced chippy, a novice dome builder using basic tools might need some luck from the geodesic gods.

It could still be a fun project... just for the sake of building one :)

Enjoy your sunday

Regards
Colin

[ Comments 6 ]

posted by
Colin

29/03/2007 15:37:32

Hi Paul,
Thanks for the posting.. it may be useful to someone :)
Just a quick revision note to the pic regarding the "B" strut edge angles, only 30 struts will be needed with the 7.23/4.13 deg angle..these are used solely for the pentagon perimeters (the red angle edge faces into the pentagon)
The remaining "B" struts (10 or 25 depending on whether a 3/8 or 5/8 design)will need a 7.23/7.23 deg angle.
These B struts are used to link the pentagons together and also form part of the hexagon perimeters.
I knew i was missing something but couldn`t put my finger on it :)

posted by
admin

04/04/2007 02:46:56

How did you workout the dihedral angle Colin? I managed to work out the end angles by using a formula I found on the net, I can't find it now but it's fairly simple to work out the angles if you know how long each side is on a triangle. I used the dome calculator to workout the radius and strut length. The radius equals two of the sides and the strut length makes the bottom of the triangle. I'll post a diagram to make it a bit clearer later.

posted by
Colin

04/04/2007 10:56:38

Hi Paul,
Take a look at the "Fastening Angle Determination" section at tekcad.com

posted by
Jero

14/03/2012 14:54:57

Hi! I am trying to do it without hubs. Just timber! Then, there is a tricky problem with A struts coming into B struts. My As cut at 60º head with 10º base angle don't fit properly on the 60º head 11,6º base angle of the Bs. And then, the problem goes to fit them perfectly when forming the pentagone in the dome.The lengths are correct from vertex to vertex, all cut to the millimiter, though model being 1,2m in diameter with 20*20 mm sticks. Don't want to go on the lumber before being certain! Any suggestions? (Sorry for copying same on both subjects :P)

posted by
Jero

14/03/2012 18:36:26

A general question regarding calculations on this 3V is, when you cut your arrow-head angles, which are the tiltings of the saw blade -ergo, the projection- to cut the 60º and 54º arrow-heads on the 10,05 base angle. Then, the tilting for the 60º on the 11,64º and the 12º. Are they those painted on the drawing??? Nice one!

posted by
Giovanni

17/07/2012 15:51:23

Hey everyone,I am building an experimental speaker enclosure in the shape of a geodosic dome. I am not starting with triangles but instead using flat panel hexagons and pentagons cut out of plywood. My problem is determining the angles the edges of the plywood should be cut to. I have been experimenting on the table saw with some trial panels and although I am close I am not getting a good fit. The angles I have been using are in the 20-21 degree range for each edge, not 10- 12 degrees. I do see now from the above illistrations that the angles should be different for the hex and pent shapes. Please, any suggestions, thanks