PDA

View Full Version : Making an aluminum dome



Too_Many_Tools
07-12-2009, 01:54 PM
I have a project that I would like to do...making a 8' aluminum dome for a small observatory for a local astronomy club.

The skeleton of the dome will be aluminum tubing (my excuse for getting a TIG ;<) ).

I am looking for insight into how to make this dome..bending, sheet metal work, ...especially the aluminum dome skin with NO leaks when we are finished.

Any suggestions, advice or warnings?

Thanks

TMT

Bmyers
07-12-2009, 02:06 PM
metal spinning would be the easiest way to make the dome.
never mind, missed the 8 FOOT dimension first reading

lugnut
07-12-2009, 02:16 PM
Two things come into mind when thinking about building a dome like you want. First would be a dome made up of triangle panels and then one made up like the segmented satellite dishes .
Mel

Mike Burdick
07-12-2009, 02:22 PM
TMT,

Here's a thread showing how someone did it with steel...

http://kuva1.kuvablogi.com/iso/img2081295.jpg

http://www.kolumbus.fi/jappervokki/Laitteet_files/image006.jpg


http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3210404/Main/3207808


Have you considered using fiberglass over a steel structure as above?


.

Evan
07-12-2009, 02:25 PM
Spinning is still an option for some...


http://metalshopborealis.ca/pics/spinning.jpg




Seriously, You should contact a very long time friend of mine and ask his opinion on this. He is the president of the Prince George chapter of the Royal Astronomical Society, of which I am a member and whose web site I host. His name is Gilbert Self and I know he will be happy to fill you in on the issues and related problems they have had with the dome of the society observatory. I am sure he will have some helpful suggestions.

His e-mail address is on the front page of thier web site. You might also try calling the number listed as he spends a lot of time at the observatory since he retired.

http://vts.bc.ca/pgrasc/

johnnyd
07-12-2009, 07:34 PM
Sounds like an ideal job for an "English Wheel". You could build it just like you would an aluminum airplane.

rockrat
07-12-2009, 07:54 PM
Watched some fellows install a copper roof. Honestly I was hoping for some scrap. :) Anyhow, they have an interesting method of creating the standing seams. Might be a possibility for you.

Outside of that, I know that the observatory I used to hang out at had to have the dome "painted" with some sort of plastic paint. I cant remember exactly what it was but they sprayed it on and it stopped the leaks.

rock~

Too_Many_Tools
07-12-2009, 07:57 PM
TMT,

Here's a thread showing how someone did it with steel...

http://kuva1.kuvablogi.com/iso/img2081295.jpg

http://www.kolumbus.fi/jappervokki/Laitteet_files/image006.jpg


http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/3210404/Main/3207808


Have you considered using fiberglass over a steel structure as above?


.

It looks like a good example.

I wonder how he is going to skin it?

What stock should be used for the skeleton...right angle, square, round, flat?

TMT

Mike Burdick
07-12-2009, 08:15 PM
It looks like a good example.

I wonder how he is going to skin it?

What stock should be used for the skeleton...right angle, square, round, flat?

TMT

TMT,

It looks like he used square tubing and made a clever little bender to roll it (see the thread). The "driving" wheel is narrowed in order to "crease" the inside edge of the tube to take up the shortened side. He used steel sheet metal to skin it (see second photo in my previous post).

How about shooting him an email? I'll bet he'll share everything he knows about it, including some tips and plans! His website address is in the thread. He can read and write English as his thread responses are in English.

His web page... http://www.kolumbus.fi/jappervokki/

His email address.... jappervokki@kolumbus.fi

http://kuva1.kuvablogi.com/iso/img2036892.jpg


.

thistle
07-12-2009, 08:26 PM
tig weld sections to gether, to make a hemishere, tig a plate to the bottom, fill with water , pump water in under pressure with a hydraulic pump until it goes round .

Evan
07-13-2009, 02:29 AM
There is more than one or two ways to make a dome. I saw this one at the Mt. Kobau Star Party some years ago. It's made entirely from Coroplast double wall plastic and does not use any of the common methods of producing a dome from flat sheets. No pie sections, no pentagons or hexagons and no geodesic polygon combinations. In fact it is made from interlocking U shaped pieces in a geometry that I didn't know existed until I saw this. It doubles as a tent and a semi rigid observing shelter. The dome rotates easily on the lower base and the entire structure only weighs around 20 or so lbs. It comes apart and becomes regular and easily stacked flat pieces in a few minutes. The fellow who had it there is the inventor.

http://ixian.ca/pics6/pdome.jpg

Tuckerfan
07-13-2009, 03:19 AM
Maybe you could modify a Kugelhaus: http://davidszondy.com/future/Living/kugelhaus.htm

http://davidszondy.com/future/Living/kugelhaus3.jpg

I can't find it, but Popular Science or Popular Mechanics back in the late 50s/early 60s did a piece on how to build a dome shaped camper trailer, which could be stacked like orange slices.

oldtiffie
07-13-2009, 04:19 AM
Some of the best I've seen are the radar/radio domes used world-wide by NASA and the CIA and at many observatories. They seems to stand some pretty rough weather and high and low temperatures.

They are "domes" formed from a series triangles linked at their "corners" (nodes). They are pretty well a single plane space frame. The triangle is the ultimate rigid structure in terms or rigidity per unit mass. The triangles are made from tube normally but also rectangular/square tubing are used as well. For external/weather-proofing/cladding use, there is a single-plane triangular "in-fill" panel fastened to each triangular unit which of itself adds to the unit stiffness. The triangular units are "roofed" or "flashed" to each other for drainage and water--tight integrity.

All triangular panel are flat, and the triangular unit frames are straight. No compound or difficult work involved at all.

Some units may be adjusted at the "node points" ("sharp corners").

Some local stiffening may be required but is simple to do. An attached space-frame/s is excellent for this purpose as their size to strength ratio is huge (not much "space" taken up at all).

The design of the units may be quite a task - ask a local observatory or a Structural Engineer for more details.

http://www.shilp.org/introductionto-space-frame-structures.html

http://www.google.com.au/search?hl=en&q=space+frame+structures&meta=&aq=9&oq=space+fra

[Edit]
After going back and re-reading the posts by Evan and others, I can say that the triangle is the simplest form of "...adron" skin type but they can and do go through heptagon, hexagon, septagon, optgan, nonagon and etc. etc.

Those above "3-sided" can be progressively bi-sected and reduced to triangles for optimal stiffness and bracing.

I'd still start at the simple triangle. The sides are not necessarily equal and so the triangle is not necessarily equilateral.
[End edit]

lenord
07-13-2009, 08:52 AM
There are always the dome kits. You buy a bunch of premade bent sheet metal triangles and bolt them together. They were intended for a house, but I see no reason they can't be made into a small astro dome... I remember seeing the ads inside the covers of mother earth news. Dome incorporated is the company.

Lenord

Evan
07-13-2009, 09:55 AM
I'd still start at the simple triangle. The sides are not necessarily equal and so the triangle is not necessarily equilateral.

It is an exercise in spherical geometry. A spherical triangle that reaches from the pole to the equator does not have the same angles that a plane triangle does. In the case of an equilateral spherical triangle it has three 90 degree angles. This obviously cannot be mapped to a flat surface which is why it isn't possible to map a globe accurately as a flat map.

Instead, one must use much smaller slices of the sphere which, as they become narrower, begin to approximate the same shape on a plane. Of all the possible ways to make a dome from flat pieces the best in respect of leakage is one in which the triangles reach from the pole to the equator since all the seams are vertical. All other types of domes suffer from leakage problems which is a major reason they are not more popular.

A second issue affects the Buckminster Fuller invented Geodesic dome. It encloses the maximum space with the minimum amount of material. While this is an admirable attribute it also is the greatest failing. In a geodesic dome every single member is a structural member and the failure of any single member compromises the integrity of the entire structure. The structure in essence is composed of a large array of single point failure units. Remove any one and the dome loses it's rigidity. It also means that the only way to safely penetrate the structure is by leaving out coverings over the hexagons or pentagons, not suitable for an observatory.

When mapping the slices that make up a dome composed of triangles the triangles will all have 90 degree angles at the base that lies on the equator. The angle at the pole will be the fraction of the circle in degrees represented by each triangle's share of the circle. The line between them will be an arc that has as it's radius the circle that lies on a plane where the circumference instersects the base at each vertex at 90 degrees and also intersects the apex. This varies depending on the number of "slices" and can easily be laid out empirically with some string on the flat. Once one part is designed all the rest are the same, not forgetting to allow for overlap on one edge of each slice.

Dawai
07-13-2009, 10:25 AM
Shoot Kerry Pinkerton at Imperial wheels a email.

Kerry Pinkerton
http://www.imperialwheelingmachines.com/




Perhaps you are on the wrong forum for this. First thing you do when someone is instructing you to ewheel is make a dome, of course it is a six to ten inch one.. but it teaches the concepts behind "stretching metal" and increasing it's surface area.

It is not hard bending metal, it is hard making it do what you want it to.. the larger the piece the more interaction from one end to the other.

There may be a local "genius" who can help you. Look out for the armchair cowboys that got the talking part over with. I think a few of them made Kerry quit playing with us normal folks.. (normal??) He's a helluva guy anyways who has done more unpaid and unappreciated Metal forming educating than anyone else I know of.

Evan
07-13-2009, 10:53 AM
There isn't any reason to make the metal a compound curve for this project. Flat pieces will work fine as long as they are reasonably narrow. The edge flange will need to be cut out every six inches or so for bending and slightly broken over with a rubber hammer on the edge of a piece of wood. Cheap aluminum flashing will work just fine for a dome this size with only a minimal framework at each seam. Pop rivets and silicone sealer will hold it together.

I would make the frame from curved pieces of 1" x 3/16" flat bar. The design of the opening slot is left to the discretion of the builder.

Too_Many_Tools
07-13-2009, 11:08 AM
There isn't any reason to make the metal a compound curve for this project. Flat pieces will work fine as long as they are reasonably narrow. The edge flange will need to be cut out every six inches or so for bending and slightly broken over with a rubber hammer on the edge of a piece of wood. Cheap aluminum flashing will work just fine for a dome this size with only a minimal framework at each seam. Pop rivets and silicone sealer will hold it together.

I would make the frame from curved pieces of 1" x 3/16" flat bar. The design of the opening slot is left to the discretion of the builder.

Those seams are where I see the biggest challenge.

I want a no leak, no maintainance, professional looking job when I am finished.

Any suggestions or PICTURES of how to do them?

And thanks to everyone contributing to this discussion.

Too_Many_Tools
07-13-2009, 11:09 AM
There is more than one or two ways to make a dome. I saw this one at the Mt. Kobau Star Party some years ago. It's made entirely from Coroplast double wall plastic and does not use any of the common methods of producing a dome from flat sheets. No pie sections, no pentagons or hexagons and no geodesic polygon combinations. In fact it is made from interlocking U shaped pieces in a geometry that I didn't know existed until I saw this. It doubles as a tent and a semi rigid observing shelter. The dome rotates easily on the lower base and the entire structure only weighs around 20 or so lbs. It comes apart and becomes regular and easily stacked flat pieces in a few minutes. The fellow who had it there is the inventor.

http://ixian.ca/pics6/pdome.jpg

Very interesting...any other pictures or leads to the builder?

Thanks

Too_Many_Tools
07-13-2009, 11:11 AM
TMT,

It looks like he used square tubing and made a clever little bender to roll it (see the thread). The "driving" wheel is narrowed in order to "crease" the inside edge of the tube to take up the shortened side. He used steel sheet metal to skin it (see second photo in my previous post).

How about shooting him an email? I'll bet he'll share everything he knows about it, including some tips and plans! His website address is in the thread. He can read and write English as his thread responses are in English.

His web page... http://www.kolumbus.fi/jappervokki/

His email address.... jappervokki@kolumbus.fi

http://kuva1.kuvablogi.com/iso/img2036892.jpg


.

Yes...I too was impressed with his homemade roller setup...a great example of doing with what you have available.

Too_Many_Tools
07-13-2009, 11:12 AM
Maybe you could modify a Kugelhaus: http://davidszondy.com/future/Living/kugelhaus.htm

http://davidszondy.com/future/Living/kugelhaus3.jpg

I can't find it, but Popular Science or Popular Mechanics back in the late 50s/early 60s did a piece on how to build a dome shaped camper trailer, which could be stacked like orange slices.

Thanks for posting this item.

Forrest Addy
07-13-2009, 12:09 PM
8 foot observatoy dome? Make a steel frame as in the photos. Cover with 1/8 mahigany plywood and fiberglass the exterior for weather tightness. 8 foot is very small unless the thing is controlled remotely or you are small in stature and/or slender.

vincemulhollon
07-13-2009, 12:45 PM
I have a project that I would like to do...making a 8' aluminum dome for a small observatory for a local astronomy club.

If the purpose is protecting a "small" telescope, don't make a dome unless your actual purpose is making a dome, because domes are cool, with a side effect of protecting a telescope.

A dome minimizes the surface area which equals cost of materials with no regard to the cost of labor, both building and maintaining. But for something that small, the materials are cheap while your labor remains expensive...

Something only eight feet on a side, you're looking at basically a tool shed w/ removable panels for roof and all walls, up on wheels. If a timber is blocking jupiter at this moment, either wait 20 minutes for the earths rotation to clear it, or if the shed is on wheels, shove the shed a foot or two. Obviously chain the thing down very securely.

digger_doug
07-13-2009, 01:27 PM
Spinning is still an option for some...


http://metalshopborealis.ca/pics/spinning.jpg



http://vts.bc.ca/pgrasc/


Evan,
You certaintly have gotten allot of mileage out of that pix....
But always appropriately.

That book (whence where the pix came) also includes making
large domes, using explosives in a pool of water.

My money is on a farm silo roof.

I had an article (from machinery magazine) on how they (bell)
would make the plexiglass domes for the bell-47 copter
(the one featured in the T.V. show MASH)

Basically pull the sheet out of an oven, quickly clamp to a form,
blow in compressed air.

A google search should kick up a couple of homebuilders dooing just
that, I went to a demostration they hosted once.

dewat
07-13-2009, 05:18 PM
I just happened to see this last week, it might give you some ideas, instead of casting the parts he is doing you might be able to buy them.


http://www.youtube.com/watch?v=UsF4qrR4TQ8

Astronowanabe
07-13-2009, 11:16 PM
unfortunately for the metalworking angle... last I checked you could get one of these for less than a decent tig welder and it is done and does not leak.

http://www.explora-dome.com/

GKman
07-14-2009, 08:01 AM
Schedule a trip to the converted MIG factory in Poland that hammers these Cobras out. That ain't silver paint.

http://img.photobucket.com/albums/v494/gkman/067600x450.jpg

dave5605
07-14-2009, 11:09 AM
Too many..... I don't want to deter you from buying the Tig (I bought one just because) but welding thin aluminum is an entirely different animal (for me at least) then mild steel.

I am a fair welder with a mig on 18 gauge to 1/2" steel but that darn TIG is another animal on anything thinner than 1/8" aluminum for me. Even 16 gauge steel is a challenge. Then again I only use it about 2 hours a month. I should practice more (a lot more) but it gets me frustrated.

Hopefully you are a more experienced welder than me (a hobbiest hack).

I have a thermal Arc 185A inverter tig and would buy one again. Then there is the Miller 200DX inverter but that's another $1000 or so. Way beyond my 'just because' budget.

rantbot
07-14-2009, 12:30 PM
That book (whence where the pix came) also includes making large domes, using explosives in a pool of water.

So, what's the title of this mystery book?

digger_doug
07-14-2009, 12:36 PM
So, what's the title of this mystery book?

"Forming Alcoa aluminum"

The Alcoa company released several books on use of their products.

Machining
Bonding
Welding
Die cast design