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  #1  
Old 15-04-2013, 03:40 PM
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My future geodesic dome

The time has come to start preparation for building the dome for my Newtonian, on EQ6.

I decided to go for geodesic, 3v..
The construction will be done in phases:
- building the basic frame elements (hexagons and pentagons with spokes), made of 19x42mm pine beams.
- building the round track, concrete slab for pier, deck (planned for end of this year)
- assembling the dome frame from pentagon and hexagon elements
- cladding the structure with triangles cut from Styrofoam sheet 50mm
- rendering the outer surface with metal mesh and polyurethane.

The dome itself will be a bit more than a hemisphere, similar in looks to this one, but 3 metres in diameter.

I was thinking about using just styrofoam (rendered with metal mesh and polyurethane) but decided to go with wooden frame to increase the structural strength - I don't want the whole thing to be blown away by high wind, since the dome will be placed on elevated ground, with not many other buildings around.
Also, the wooden frame allows for build-in storage boxes and working surfaces for equipment.

Wish me luck with this project
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Last edited by bojan; 22-04-2013 at 11:46 AM.
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  #2  
Old 15-04-2013, 04:12 PM
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sheeny (Al)
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Good luck, mate. Make sure you keep us posted. It looks like it should be an excellent project.

Al.
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  #3  
Old 15-04-2013, 05:41 PM
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ZeroID (Brent)
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Yep, good luck with this Bojan. We'll be watching.
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Old 15-04-2013, 05:46 PM
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Fantastic, I would love to see it one day. I remember meeting you and your wife at Johns hill.
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Old 17-04-2013, 09:09 AM
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bojan, I'm not sure what sort of finish polyurethane gives you but it might be worth while looking at a arcrylic render finish. Taulbmans armawall roll on render can be applied directly to styrofoam, no mesh, and gives a hard finish. It comes pre mixed in 15L containers and before application looks like really thick paint with .5-1mm stones through it. I applied it to mine with a trowel and once set, I gave it an acrylic texture top coat. Mine was hit by cricket ball a while back, leaving a small impact crater which I just slapped some top coat texture over to seal it. It's pretty tough stuff.
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Old 17-04-2013, 03:49 PM
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Bojan, that is going to be one very solid dome! Your choice of materials should provide a good measure of thermal insulation too. My 3V dome from plywood (without any frame) is very rigid - even after the aperture opening was cut. Some pics here http://www.iceinspace.com.au/forum/s...t=36222&page=2 (see posts ~#44)

Have you worked out the width of your aperture yet? Don't underestimate how far off-centre a GEM will put the scope! I'm almost on the limit for mine (at nearly 700 mm), but a narrower opening = more shelter for the scope and operator.

Looking forward to more progress reports.

Chris
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Old 18-04-2013, 06:13 AM
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Guys, thank you for kind comments.
I will certainly post updates on project progress, as it advances..

Quote:
Originally Posted by Tandum View Post
bojan, I'm not sure what sort of finish polyurethane gives you but it might be worth while looking at a arcrylic render finish. Taulbmans armawall roll on render can be applied directly to styrofoam, no mesh, and gives a hard finish. It comes pre mixed in 15L containers and before application looks like really thick paint with .5-1mm stones through it. I applied it to mine with a trowel and once set, I gave it an acrylic texture top coat. Mine was hit by cricket ball a while back, leaving a small impact crater which I just slapped some top coat texture over to seal it. It's pretty tough stuff.
Robin, thanks for comment - I will certainly have a look at that.
So, you didn't try to use any kind of mesh?
I was thinking, metal woven mesh may give me the additional strength in case of hail impact...


Quote:
Originally Posted by ChrisM View Post
Bojan, that is going to be one very solid dome! Your choice of materials should provide a good measure of thermal insulation too. My 3V dome from plywood (without any frame) is very rigid - even after the aperture opening was cut. Some pics here http://www.iceinspace.com.au/forum/s...t=36222&page=2 (see posts ~#44)

Have you worked out the width of your aperture yet? Don't underestimate how far off-centre a GEM will put the scope! I'm almost on the limit for mine (at nearly 700 mm), but a narrower opening = more shelter for the scope and operator.

Looking forward to more progress reports.

Chris
Chris, your work inspired me to take that challenge.. apart from a need to cut cost (pre-fabricated domes are terribly expensive).
The thermal insulation was something I thought of when I was browsing your thread couple of years ago.. when I was considering whether to buy or to build.
But those days I was working full time, and now I am in "forced" retirement (made redundant last year, and the job market for old, one-foot-in-the-grave RF engineer is very limited recently) - so cost became a major issue - and as at the moment I have enough free time to build myself, I decided to take that approach.

My opening will be 60cm wide - it should be enough for both for me and my 10" Newt, even at zenith (the eq centre-to-centre displacement is 34cm).
It will be a bit of the problem for synchronisation of dome and EQ and meridian flip, but this is something to be dealt with in the future.

For now, I am running a production of hexagons (using the template).. 13 + 2 1/2 are needed.

Last edited by bojan; 18-04-2013 at 07:11 AM.
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  #8  
Old 18-04-2013, 11:40 AM
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Quote:
Originally Posted by bojan View Post
So, you didn't try to use any kind of mesh?
I was thinking, metal woven mesh may give me the additional strength in case of hail impact...
Not once I found this taulbmans stuff. A lot of people where telling me to fiberglass it but I'd done a little of that before and never wanted to deal with it again. I was planning to mesh it and use mix youself bags of acrylic render from bunnings. The mesh simply gives the render something to cling to, I wouldn't have thought it would impart strength. You'll be surprised at just how solid a dome is once built. You might want to check with a paint shop to see if the taulbmans stuff sticks to wood but here it was sticking to everything like you know what to the proverbial blanket and if it's under coated in the first place it should be fine. I think dulux make a similar product.

I had to buy the render, it was $130 for 15L and I used one drum, but I did get the top texture coat off ebay really cheap. I had already sealed the dome with external acrylic from another job and had coated it with a texture paint I found on the bunnings throw out pallet which gave it a sandpaper like texture. If you look in the shutter section of the obs build on my site you'll see the many colours of the dome before it turned white with the render

Here's a pic of where the dome was struck with a cricket ball. It cracked the render so I just slopped some top coat over it to reseal it.
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  #9  
Old 19-04-2013, 07:27 AM
el_draco (Rom)
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New Dome

I'll be very interested to see you progress on this. I've just laid all the cabling to the location I want to put my observatory and am in the design exploration phase a.t.m.

Very demanding process! Location for me is a significant issue. No possibility of a crane on site to lift a dome so I suspect its going to be build on the spot, probably a 3/4 geodesic very similar to yours....
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Old 19-04-2013, 03:21 PM
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Robin,
your website is very interesting for me.
I will definitely consider acrylic overcoat, when the time comes for that (later in 2013).

Rom, I have the similar issue with my future site - it cannot be (easily) reached by crane so that is why I am doing frames only for now, as a first phase of the project - preparation for the final assembly.

Since in everybody's experience the styrofoam only (over-coated by acrylic or whatever) is stiff enough once assembled into dome, I will probably omit pentagon frames and insert styrofoam-only pentagons in the remaining places (I still think the additional strength achieved by wooden frame is not an un-necessary overkill)

Of course, styrofoam elements (styrodur actually - it is much stiffer than styropor and will cost me $25 for 2500x600x50mm sheet, 18 sheet all in all) will be inserted over the frame once the frame is fully assembled, on the wheels and so on.
Btw, I found pine beams 19x42mm for 55c per metre.. cheap (~130m required.. not a first class material, but still very low rejection rate, ~5-15%).
I am gluing them together with Selleys liquid nails (classic) with the help of a template and staple gun.

Currently my production rate is 1~2 hexagons/day. It could be faster (limited by one only template and the glue setting time.. all timber spokes are already cut to required size), but I am not in a hurry.

Last edited by bojan; 19-04-2013 at 07:05 PM.
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  #11  
Old 19-04-2013, 04:25 PM
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Looking good Bojan
I'm glad you are finally underway with your dream.
It's a great feeling.
I hope it doesn't turn out too heavy.
What is the projected weight of the geodesic, all up?

Steve
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Old 19-04-2013, 04:47 PM
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Hi Steve, yes, the dreams are on their way to here
I think it will be close to 110kg (more if I go with wheels on the fundament and steel track as part of the dome)
I plan to use 10 wheels (at the corners of each lowest hexagon).. should be OK...
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Old 19-04-2013, 09:08 PM
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With that design I'd suggest you look at a bent pipe on the ground and wheels to suit on the dome.
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Old 20-04-2013, 07:52 AM
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Quote:
Originally Posted by Tandum View Post
With that design I'd suggest you look at a bent pipe on the ground and wheels to suit on the dome.
Robin, thanks for suggestion - that's exactly what was on my mind, so now I know it's not a stupid idea
I just have to work out the details - what kind of pipe (square or "L" or "U" channel profile), how many sections (I can't have it in one piece - too big for transport), how to assemble it in situ (welding for pipe? screws for bent "L" profile or "U" channel?)..
This will depend on my friend (the one with work shop) and his capabilities (or preferences..)
The part of this formula is also motorisation.. and how to mount the cogged belt or curved rack pinion on a dome - I liked your approach - I used similar interface for encoder on my dobson mount, this is way cheaper than the gear made to fit the existing situation, but quite good enough.
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Old 20-04-2013, 08:06 AM
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Bojan,
Back in South Africa, we had a member who built a rotating observatory and used a 100mm PVC pipe bent into a circle as the base runner. It was semi recessed into the concrete foundation. He then used two rubber wheels @45 degree (I think 6 sets in total) to run on the top of the PVC pipe.
Hope this helps.
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Old 20-04-2013, 09:22 AM
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Hi Ken, this is also an option, thanks for suggestion..
Do you know how the PVC behaved on high temperatures (sun)? I will have 130kg of dome on it (hmmm, the weight will be distributed along the length of the pipe through the wheels.... and the pipe is supported by the recession into concrete.. food for thought.. maybe pipe should be filled with concrete? cheap and easer than metal but possibly good enough.. I will try to experiment when the time comes.)

EDIT:
Being PVC, I imagine it is easy(er) to slightly adjust the final radius of the curved pipe base runner, by simply tightening some kind of the rope (steel?) inside, before filling it with concrete)... so for every cm in radius, the circumference (the length of the rope) must be changed by 6.14 cm..
Interesting...

Last edited by bojan; 20-04-2013 at 10:35 AM.
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Old 20-04-2013, 10:22 AM
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Here's a couple of pics from Joe Garlitz, the guy who put the foam dome plans on line in the first place. He's driving his dome like this and gets accurate positioning. The cog drives the home made belt and the magnet clicks the switch as the spurs pass by. I thought it was pretty clever.
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Old 20-04-2013, 10:33 AM
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Looks good..

I was also thinking about rack (will have to be curved first.. if possible at all), normally used for sliding doors ( I have it on my gate)..

And.. I have one old, spare motor driver unit ("Nice" brand) somewhere in the shed.. and wireless remote controller that goes with it as well.
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Last edited by bojan; 20-04-2013 at 12:44 PM.
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Old 24-04-2013, 06:57 AM
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Nice one there Bojan. I built a "sorta" geodisic 5 years ago and have no regrets at all.
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Old 24-04-2013, 07:32 AM
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Nice one there Bojan. I built a "sorta" geodisic 5 years ago and have no regrets at all.
Hi Chris, thanks for kind comment..
Do you have some pics of your dome?
I haven't decided yet about the track/wheels design, so any input is still most appreciated
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