whose plywood dome?

[Dick Fischbeck]

I forget where and who this is from. 

[RC]

That was mine.

-Robert Clark

[Travelling Telescope]

Hi all,

I have a question mainly to Robert Clark (great dome btw!!) but anyone else interested in helping me too!

I run a planetarium in Nairobi, Kenya, and our screen needs replacing.  Our dome is a 3v Krusche bamboo structure a fraction under 10m in diameter.  We always talk about sustainability in our dome, and so I'd love to make our screen out of locally available, natural materials, using local labour.  My ideal plan is a woven pattern something like this:

I am imagining a series of panels made of hexagons and pentagons of perhaps a meter across.  These could be suspended from the main frame (around a 30cm gap from the outer structure), and would need to be joined together with a minimal seam.  

This is my dream!

However, I've never woven anything in my life and am only just learning about dome geometry from the dome we built (also a first for me!).  I would imagine needing a hexagonal and a pentagonal template and after making each panel they would be woven into the structure, but I have no idea how to calculate or visualise all that and then to explain it to a local weaver.  Would anyone be interested in helping me with this? Or any thoughts at all - is this a terrible idea?!!

Thanks in hope!!

Chu

(by the way, here is a link to our website)

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[Ashok Mathur]

Dear Chu

I was briefly associated with a revival of a planetarium in rural Maharashtra . The German projector had broken down and lay unused for some decades when a German visitor came to the village and found and set it right with his own money. He was clear that screen had to a 4 v dome and not a 3v dome as that was too far from an ideal spherical surface. I supplied the calculation for the 4v surface. Such a surface , with a given radius, costs about 40% more than corresponding 3v dome.

But I support going 4v.

Some time ago I had come across a specialised group that dealt with domes in planetariums. I will try to find it again.

By itself , the bamboo basket weave, is too irregular for use a screen.it needs to be made smooth with a layer evenly spread over it. a fine clay layer would be a good choice.

When making large parabolic surfaces with a smooth finish, the trick is to use a mold repeatedly.Such moods are cheap to make. Can share details if it interests you.

Regards

Ashok

Sent from my iPhone

On 11-Oct-2022, at 8:52 PM, Travelling Telescope <daniel...@gmail.com> wrote:



To view this discussion on the web visit https://groups.google.com/d/msgid/geodesichelp/CAApebLxSQKVUTKYkh-KSWCg1WC5be3Wp6kaHsFebKc5B7a595A%40mail.gmail.com.

[Dick Fischbeck]

Chu- Here are a couple of links on triaxial weaves I know about. They might give you ideas.

https://www.youtube.com/watch?v=KEwKtsGnnlc

https://hexdome.com/weaving/triaxial/index.php

https://www.antiprism.com/album/830_woven_polys/index.html

On Tue, Oct 11, 2022 at 11:22 AM Travelling Telescope <daniel...@gmail.com> wrote:

Hi all,

I have a question mainly to Robert Clark (great dome btw!!) but anyone else interested in helping me too!

I run a planetarium in Nairobi, Kenya, and our screen needs replacing.  Our dome is a 3v Krusche bamboo structure a fraction under 10m in diameter.  We always talk about sustainability in our dome, and so I'd love to make our screen out of locally available, natural materials, using local labour.  My ideal plan is a woven pattern something like this:

[Travelling Telescope]

Thanks so much Dick and Ashok - I really appreciate your help on this.  I am aware the woven approach will be a little uneven, but to be honest I'm positive it would be better than what we have now (a pinched, suspended fabric screen stitched out of 8 large sheets - it works but I want it improved).  The trouble with a clay or plastered layer is weight and airflow, hence my thinking about weaving.  I will try the triaxial approach on a small scale and see if it can work!

Thanks again!

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