Dome

Hi
How can I make a 13cm raduis dome, that i can then cover with fibreglass,
out of household materials?
Thanks
Michael
Reply to
Michael
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Radius I mean.
Reply to
Michael
Use a ball as your mould.
Reply to
Airy R. Bean
How accurate (sphericity/dimension) does it need to be?
Reply to
ChrisH
About 5mm either side of 26 diameter.
Reply to
Michael
Michael wrote in message ...
Could you find a toy ball of the right dimension perhaps?
Bob
Reply to
Bob Minchin
Half a sphere good enough? You could mould some sand by making a baseboard with a perpendicular bar to carry a former the shape of the dome. By turning the former 360 you can carve a pile of sand into shape. This method has been used to make microwave dishes. The pile of sand as formed can be fibreglassed. I can't remember which book I've seen this written up.
If you mix dry cement with damp sand, it will harden, giving a shape to work with. You don't want it too hard to easily remove from the fibreglass dome...
Steve
Reply to
Steve
fibreglass,
Hi
Thanks for all the replies. Yup, it is a half sphere. Ill try that sand method, its sounds promising.
Michael
Reply to
Michael
Hmmm. Well you try inflating a round balloon to the correct diameter, coat it with plaster of paris and plaster-soaked rags (which will harden quickly), that would then give you a spherical mould. If you want the OUTside of your fibreglass dome to be smooth you then need to make an inverted mold from the plaster one.
ChrisH
Reply to
ChrisH
The top of a balloon covered in papier-mache? Perhaps not a perfect dome, but it would be smooth and you can inflate the balloon to get the diameter correct.
A standard football is 22cm wide, so perhaps a cheap plastic football could be warmed and over-inflated.
Tim
Reply to
Tim Auton
Go and talk to a blow moulder and see what they already have that they do for other folks. Vacuum formers are also worth talking to.
The big bird warning globes that hang on power lines for example, and there are probably decorative globes that can be picked up.
Just a couple of thoughts...
Peter
Reply to
Peter A Forbes
Alternatively, get a ball slightly larger ( wall thickness is going to be about 3mm at a guess ), slice it in half and you have a ready-made mould you can fill. The ball will probably be flexible enough to allow you to peel it off the fibreglass matrix when set. Might be an idea to use the ball to make a hemispherical impressing in a bucket of damp sand first, to give you somewhere to pop the mould while the fibreglass sets.
You'd need a fairly stiff mix of resin to prevent the matrix from slacking though. I'd be inclined to build it in layers.
Regards,
Reply to
Stephen Howard
RSGB VHF/UHF Manual (Page 8.56 in the 3rd edition).
Steve R
Reply to
Steve
make a mould from a childs plastic ball after checking dimensions are within tolerance I think balloons will not achieve stated accuracy requirement. As stated previously depending on which side is required to be fair an intermediate mould may be required. This can be GRP as well if it is properly waxed and polished and release agent is used. For high density moulding consider "vacuum bagging"
Reply to
Chris R
Have a look at:
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It might help...
Reply to
Jon Sutton

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