Big Vacuum form molds - best method

Mar 25, 2005 1 Replies

I need to make large, 15"x40"x1-2" deep, molds for vacuum forming. I will have a pattern that is slightly convex (imagine the top surface of an airfoil) and I want to cast a female mold over it. I have been told that bondo makes for a strong, cheap material to use, but I am concerned that my large part will be difficult to do this way due to the quick working time of bondo and its thick mass. I was hoping there would be a thin resin that would dry very hard (heat resistant too) that I could brush over my pattern and then reinforce it with fiberglass or mat material to build up a thichness that would be strong enough. Perhaps fill in the female mold's underside with a light weight filler.



Does the latter method make sense, have others done it this way and any recommendations on the materials to cast over the pattern? Do I need thousands of dollars to do this or is there an economical way?



Thanks for any help on this,



Wade Posted at:

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Bondo is not strong. Bondo is only cheap. I don't think that it tolerates heat very well. You could make a pattern from wood. You could try using a plaster like Ultracal 30 with some type of reinforcment (ie burlap or wire mesh) . There are a number of castable and brushable aluminum filled resins made specifically for constructing vacuum forming molds

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a combination of wood and one of these resins might work or casting the whole mold from one of these resins.

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