Need advice on making a mold on a Sphere.

[xHOBOPHOBIAx]

I have a 20 inch polycarbonate sphere. I need to make a mold of a 12 inch section of the top of the sphere, use the mold to make a plaster plug to vacuum form over. What would be the best way to make the mold off of the sphere?

 

[TazMan2000]

If you could post a picture of what you're trying to cast, it would be easier to provide some advice. The problem being is that we have no idea of what detail from the sphere you're trying to replicate.

TazMan2000

 

[xHOBOPHOBIAx]

If you could post a picture of what you're trying to cast, it would be easier to provide some advice. The problem being is that we have no idea of what detail from the sphere you're trying to replicate.

TazMan2000

Just the shape of the sphere. There's no detail. I need to make a skin to attach to the sphere.

 

[TazMan2000]

Oh, ok. This would be the easiest way, but not necessarily the cheapest when you count in how much RTV you may have to use. I would use a plastic bowl, maybe an old tupperwear one. Ensure it is about 1-1.5 inches over the diamater you want to cast. Pour in your RTV mix to about 1 inch from the top. Them plop on your sphere. You should have some spillover of RTV so you know that the sphere is in contact with the RTV. A couple of the problems with this method, are you will need to use a lot of RTV depending on the curvature of your bowl, the other is that air bubbles rise, so you may not get a clean and smooth casting.
After the RTV sets, pull off your sphere and drop in your plaster.

There may be some other ideas out there, so I'll let others chime in as well, and you can chose the method that best suits you.

TazMan2000

 

[Kailon]

If you're just looking to mold a portion of the sphere you could section off around the molding area with a clay wall and then brush on silicon and later a plaster layer, this would at least stop any silicon from just dripping down past what you need.

 

[Darth Lars]

I would look for a ring of some sorts that I could place on the sphere and build the clay wall on top of. Also, use clay around the base of the ring to prevent it from slipping.

BTW... BB8?

 

[ultraman]

i would just get some silicone and the thickening agent and make it pretty thick then brush it on the top of the sphere in 2 or 3 layers then you could use a marker and draw out what you need and chop the rest off with scissors...bang your done! :cool

 

[clonesix]

I have a 20 inch polycarbonate sphere. I need to make a mold of a 12 inch section of the top of the sphere, use the mold to make a plaster plug to vacuum form over. What would be the best way to make the mold off of the sphere?

You have a 20" polycarbonate sphere? By any chance, do you mean Hemisphere? There is a BIG difference, and that would change everything.

I am going to make the assumption that you actually have a hemisphere and not a full sphere. If I am wrong, I'll adjust.


Can you put the hemisphere on the vacuform table and vacuum right over it?

Can you fill the inside of the hemisphere with stone to make a vacuform plug?

Can you look up "Hemispheres" on the internet and order a 20" model and cut it to the right size?


These seem like a better plan of attack than all the effort (read: COST) to mold and cast the hemisphere, only to have another hemisphere of the same size. If my assumption is wrong, and you do have a full sphere. I would go with #3

 

[xHOBOPHOBIAx]

It is a full sphere. It has a hole in it because of how it was manufactured, but it's a sphere. Like the globes you see on street lights.