Help with casting & mold making

[theHman]

Hey guys and gals,

I am in desperate need of help and advice for a casting project I'm working on.

Here's what I'm trying to do:

I've nearly completed my tyranid spore pod and want to create a master mold of it and then cast a bunch of minis from it.

Here's a pic of the pod to give you a better idea of my project.

http://i783.photobucket.com/albums/yy118/theHman99/pod2.jpg

The dimensions are:

Less than 6" wide, by 6" deep, by 5" tall

Yes, this equals a huge cubic area, that's why I've been researching and looking into "slush casting".

If you've got any casting experience (but especially with slush casting), I would love to pick your brains as to what materials to use.

I've looked into Resin, but it's pretty expensive, even when using less material that a slush cast uses.
And I'm currently looking into using hydrocal instead.

My questions are:

1. Is Hydrocal a good material to use to cast using the slush casting method?

2. Is smooth-ons OOMOO rubber good enough to create the master mold with if using Hydrocal?

Any other tips, advice, informative websites are greatly appreciated!

[Diehard]

Making the mold with oomoo is fine and it is really easy to work with. Looking at the size of what you want to cast i would recommend against using hydrocal. It will make for one heavy piece and you my have problems with bubbles. Instead try using Smooth-Cast® ROTO resin and expanding foam to fill the rest of the cavity. The trial size is $25 and should get you at least 4 thick skinned versions or 6 thin. A can of expanding spray foam is $5.

This way you have a lighter piece that still picks up all the details and you don't have to worry about chipping if it gets dropped. I am working on some bunker molds that use this same setup and have used it before for some prop weapons from a student film.

[theHman]

Thanks Diehard!

Will definitely look into that and give it a try.

[Ordo]

thats amazing looking. howd u get the leaves to stick together

[theHman]

Thanks Ordo!

I used a glue gun. Then made a very watered down mix of water, PVA glue and wood glue and painted it over the leaves to give them a light seal so that the mold remover doesn't get absorbed by the leaves during the molding and casting process I'm going to try.

[BDub]

Your best bet with that will be to use a paint on latex and then structural support with plaster bandage. Then slush cast with a semi-flexible casting medium of some sort.

You will end up with hollow light casts that can be trimmed up at the bottom and used.

However, that basing material should have been left off. It will give you all kinds of problems regardless of what you end up making the mold from. Next time make the basic model, mold then cast and then base all of them afterwards.

[theHman]

@BDub: Thanks for the tips!

I'm working on a 2nd, slightly smaller model to try with.

Keep your fingers crossed for me! =)

[Lane]

Hey guys and gals,

I've looked into Resin, but it's pretty expensive, even when using less material that a slush cast uses.
And I'm currently looking into using hydrocal instead.

My questions are:

1. Is Hydrocal a good material to use to cast using the slush casting method?

2. Is smooth-ons OOMOO rubber good enough to create the master mold with if using Hydrocal?

Any other tips, advice, informative websites are greatly appreciated!

1) AFAIK Hydrocal is a bit thick/ heavy for slush casting

2) check the Smooth-on site for mold material silicone or urethane rubber specific for plaster/ hydrocal/ concrete maybe email for suggested product

You should be able to slush cast as Diehard said.
Two tips:
Split the model into two parts, the pod and the base. That way the base can be made heavier for stability.

Since you want to slush/ roto mold you will be handling the mold while casting. To avoid distortion use a mother mold. Put a 1/4" layer of clay over the model and make a two part shell over the clay from plaster, fiberglass or whatever as long as it will hold up to handling. Make sure you have a way of holding the master inside the shell for the second part. Now remove the clay, put the master back in the shell and pour in the RTV, remove shell when cured. Cut the thin RTV mold to remove master, do not use straight cut you want to make keys to line up edges as you cut. Make an RTV plug for the open end of mold. Now you have a mold using a minimum of RTV that is still strong enough to handle and the plug allows you to fully rotate the mold.

--
Lane