Thomas Stender
Posts: 18
Joined: 2003-07-06
Location: NY
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I use insulation foam all the time for molds. I don't know if that's what you mean by expanded polystyrene, but here's how I do it:
For simple curves, I make a pattern of the curve with one straight side (if possible), trace it on 2" foam, band saw enough pieces to make up the width I need, and glue them together and to a piece of 1/2" MDF or plywood on the straight edges. The plywood is exactly the size of the stacked straight edges. Glue with contact cement or carpet tape. Cover the mold with 3 mil plastic and it's ready to go.
For bigger molds, I sometimes make a template to use with a flush router bit in a router table.
These foam molds compress a tiny bit, but hold up indefinitely.
2" foam insulation is available in 4' x 8' sheets at lumber yards.
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