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# IDEAS... How to make a 4m diameter hallow sphere ?? Answered

Hello all this is my first post on Instructables so thanks for taking the time to read !

I am looking for ideas on how i could manufacture a perfect, hallow, fibreglass sphere measuring around 4 metres in diameter (BIG) :)

I have experience with using fibreglass but I am running out of ideas for how to make a plug on this scale and get it to be perfectly spherical...

It has to be made from Fibreglass so i am really asking for help on making the mould.

ANY help or suggestions would be gratefully received no matter how wacky ....I am willing to try anything. If your idea works I will be more than happy to name the first of these epic spheres after you !!

All the best

Ben

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## Discussions

Im with toga_dan, you would need to break this up into multiple pieces that are bolted together.

Because of the scale of your project, I would take inspiration from how they create dome houses / geodesic domes. You can create a ball out of triangles arranged in a pattern. You can find the size and shape of triangle needed with some good old fashion math then make a mold and simply duplicate the part.

See the image below for a geodesic ball.

https://goo.gl/images/UTxzd2

Like this a lot, this frame would be ideal as the internal structure.

I am generating a 3D model of a 1/8th sphere, I am thinking it may be possible to use a CNC router to shape a rigid modelling board (in layers) to build up a perfect 18th of the sphere. I could then layer the fiberglass directly onto this to build the mould.

Then make 8 of these and bolt together..... the modelling board is pretty expensive but this method should give me the quality I am looking for.

great to here it was helpful. Just out of curiosity why are you making a fiberglass sphere?

take a look at water park slides. Substantially, the strength comes from the shape of the fiberglass. no Steel required really.for your sphere, bolts for most of the joints makes sense. for the last piece, Try casket Locks

area is 4 pi r^2 or 50m^2

how strong does it need to be?

how thick do the walls need to be

what is the budget for this? 50 square meters could add up.

It does need to be pretty strong, my plan is to reinforce the fibreglass 'skin' with a metal or wooden structure inside.

I would expect a wall thickness in fibreglass to be around 5-6mm.

Budget is immaterial at this stage, I need to be able to create more than one of these so I am expecting the manufacture of the mould or plug to be pretty expensive.

I have thought about using a weather balloon, inflating it to the correct size, securing it in a frame and then building up layers of very thin paper mache to get a hemispheric shape and then use this to build layers of fibreglass onto. my problem is maintaining the perfect sphere shape while loading material onto the balloon

I've got a fair idea of how I would do it at this point. but it's contingent upon exactly how spherical it must be, strength needed, Etc.Can you tell us about what this thing is for?

This does need to be as spherical as possible, the aesthetics of the outer surface are key to its use. It will be sat on the ground (on a mounting pad) but will be required to support roughly the weight of 3 adults inside but I am intending for this load to be carried into the mounting pad by an internal frame so the load on the spherical fiberglass skin will be relatively low.

I like the skeleton frame idea for the internal structure, this would be ideal.

several pieces each maybe 1/8th of sphere bolted together .

Yes I like this idea, it would be easier to get an 8th perfect than go for the whole thing in one go.

iirc, I've seen water tanks made in this fashion. bolted together in sections. I suggest doing an image search for such things.

If the swimming pool contains 33m cubed of water then yes it is like a swimming pool :)

Dig a 4 meter diameter hole in the ground 2 meters deep. You will need a semi circular template that you can drop in the hole to get the shape right. Plaster the sides of the hole and fiber glass from the inside. Good luck lifting the fiber glass out, do it again and join the 2 halves together.