"Open-top moulds: viable?" Topic

Or am I just being lazy?

I've done Prince August metal homecasting for years, and I'm thinking of having a dabble in RTV mould making.

Here's the proposition; if your sculpt is flat-bottomed, do you need a two-half mould?
Can you make a one piece mould, and just… fill it to the brim?

I'm thinking of sci-fi grav vehicles – flat, or at least featureless bottoms, smooth shapes for easy extraction, basic hulls only, so different turrets and whatnot can be stuck on at leisure.

Will I get a surface-tension meniscus like the curvature of the earth?
And if so, can I 'skim' it with the edge of a steel rule, or whatnot?

Advice & suggestions welcome!

It's doable.

You'll just have to sand them down to get them flat, along the edges.

No need for a two-part mold.

All my martian empires vehicles are done this way and sanded flat

Mike

It's pretty obvious from looking at them that a lot of resin vehicles, ships, etc are cast that way.

All my Hirst Arts molds are open topped, but of course I'm casting with dental plaster, not metal. I imagine different materials will have a differing degree of meniscus, maybe depending on the viscosity and the time to set.

Doug

Casting metal gives you the meniscus problem which varies according to the metal mix, some give more others less. It can be pretty easy to just clamp a sheet of aluminium or other hard to solder metal to the open side. Resin gives a thin meniscus going up the side of the mold which is easy to remove.

I suspected as much, but thought: "I bet there's a catch."

Thanks, gents!

If it's resin just lay a piece of glass on top with a thin coat of petroleum jelly for mold release.