Making 2 piece mold on round object

[Brian_216]

So to simplify let's say we are making a 2 piece mold of a glass beer bottle. Rather than gluing up a parting flange to separate the halves I want to use a box and pack sand around one side of the plug. I then need something self leveling I can use as a flange that can be poured over the sand and let to cure before applying gelcoat and glass to build the first half. (Melted wax, plaster etc) once the first side is done I'll just leave the part in the mold I just made and lay up the opposite side.

And go with your ideas.....

 

[OCD Solutions]

I use modelling clay and a silcone mold compound. That way I can also press indentations into the one half so that the halves interlock in perfect alignment.

Cover half the mold in clay, pour the other half, remove the clay, apply a mold release agent and pour the second half.

 

[hydrostyler]

To use readily available materials and keep it cheap, you could always use a bag of quikrete portland cement and slowly pour it in the beer bottle/exhaust chamber?? box. As it hardens, you can push small steel guide pins in (like flywheel cover or pump pins) Pour a thin layer of 635 to smooth the surface and then unleash the pva...