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Vacuum molding help!


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Hey Guys,

 

Anybody out there have any experience with vacuum molding?

 

I'm going to try making a silicone mold of some pre-made scenic bases. I've done it before with this stuff but had only limited success due to air bubbles. I've heard about some fancy schmancy vacuum dealybob that pulls the bubbles out but don't want to shell out even more money for equipment. I was wondering if I could jerry rig something with my daisy seal-a-meal. I have a large canister with a lid for use with the system and was thinking of putting my poured mold inside it and suctioning out the air.

 

Would this work?

 

Thanks,

Jen

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You're actually talking about making silicone molds, and using a vacuum pump to remove the air bubbles, not vacuforming where you stretch a piece of heated plastic over a vacuum mold and let the vacuum shape the plastic, right?

 

I haven't done that, but I've stumbled across the following two websites earlier that seem to have some good resources for those doing mold making.

 

www.smoothon.com and www.alumilite.com

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Hello there,

 

I had the same question long ago and asked a co-worker of mine that did this for a living. For large batches, yes, he'd use a vacuum rig to remove bubbles, but for most items he suggested pouring in the silicone in a very slow / thin stream/ribbon off in a corner. This had two effects. The first was that bubbles tended to pop once in the thin stream. Two, the silicone would slowly flow around the original, forcing potential air pockets out. Assuming you don't have deep undercuts, the gentle flow of the silicone should give you a pretty bubble free mold.

 

I've also kept a toothpick nearby to gently tease out any bubbles that I see (if you're allowing a slow flow, you can actually see potential trouble spots).

 

Another technique is to first lightly coat the original with a skim coat of silicone applied with a toothpick, old brush, popsicle stick. Again, you can ensure a bubble free surface if it's a thin coat. Once satisfied, go ahead and pour the rest of your material in. The critical area (for cold casting anyways) is the surface right up against your original. You can have bubbles in the thicker mass of the mold, just not marring surface detail. I'm not sure if this holds true for people casting hot materials in the molds (whether the air pockets pose a potential danger).

 

After the pour, lightly tap the base to loosen and help bubbles rise to the surface.

 

Hope this is helpful.

 

-A(occasionally back from the dead)Whang

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