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Building a large sphere, how to frame?

18811 Views 15 Replies 11 Participants Last post by  Mellony
Hey everyone, I'm trying to devise a way to build, well, a Death Star prop about 5 feet in diameter or so.

I've been doing some small scale tests with paper mache and such, but my core problem is how to create the armature/framework upon which it will be built?

My only condition is that I have to retain the ability to access the inside in order to have it backlit. I'm planning on drilling pinholes through surface to light from behind, ala Star Wars.

I've contemplated chicken wire on the outer surface, but I keep coming back to my core problem--how to concoct a sphere and/or curved ribs around a core frame. And what that frame looks like. I keep running into basic overengineering issues here.

Any ideas, suggestions are greatly welcomed! Thanks!
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· Going bump in the night..
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I'd say a PVC frame would be great for this.
Electrical conduit PVC is pretty cheap ($1.50 or so for a 10 foot length).
Quick look at how much needed:
Diameter of your Death Star: 5 feet, so circumference is about 15 feet (really it's 15.7 feet, a touch over, but rounding down barely looses size).
So, 1 and half pieces of conduit per loop = $2.25 per loop, give or take.
6 vertical loops is $13.50
At least 1 loop horizontal to give stability, so add $2.25 for $15.75 for the PVC frame.
Then you can add chicken wire, cardboard, mache, monster mud, etc. on the outside.

Curving PVC is simple (time consuming, but simple) - draw your curve as a template, then use a heat gun on the PVC. Once it's softened, bend it to (roughly) match that curve. You'll have your hoops in no time.
Use duct tape to bind the joints, or bolts if you're really wanting to be certain.
 

· Going bump in the night..
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GodOfThunder, I'm going to add to / change up my first response with the suggestion of a metal framework inside

Use galvanized 1/2 inch conduit instead of the PVC, as the weight of paper mache and other sculpting materials may even be a bit strong for the PVC.
Like this stuff: Galvanized conduit

The weight might be a factor, but it shouldn't be too bad, and the strength of steel will let you do a lot more with it once it's constructed.

As for weight? Well, since the steel is much stronger, you may be able to get by with 3 vertical loops, compared to 6 with PVC, and one horizontal.
The galvanized is as long as the PVC, so still 1 and half lengths per loop.
4 x 1.5 = 6 lengths of conduit.
Each length is 3 pounds (according to Home Depot), so 3 x 6 = 18 pounds.

(compared to using 1/2 inch PVC - 7 loops - 18.9 pounds)


This will still give you the hollow, unblocked interior you were aiming for, so you can set up interior illumination and poke holes in the exterior to let the light out (for that kick-*** Death Star look).
 
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