Quote:
Originally Posted by Bicycle Bob
Fiberglass cloth will print through and do all sorts of irregularities if messed with when the resin is green enough to accomodate a 3-D shape. You can use stretched membranes to improve the finish on male shapes, but I've not heard of a vacuum bag being used to give a molded part two good surfaces.
For putting a nice skin on foam, here's a new spray-on coating:
Industrial Polymers Corporation-StyroSpray
I've also had good success producing mold bucks (one-use master shapes) from foam covered with easy-sanding wall filler and then painted. I had a mix of latex paint, spackle, and microbaloons that sanded as easy as regular 2-lb insulation foam, but could get a hard, shiny surface by being coated with either PVA or Shellac and polished as usual. |
Thanks Bob, StyroSpray or similar is so far my first choice in making a hard, smooth male mold for my proposed Porsche nose. I'd use an armature with hotwire cutting tools for the foam cutting, followed by StyroSpray, then sanding using the same armature, replacing the hotwire cutter fist with a sprayer and/or squeege to apply the StyroSpray, then with a random orbital sander. Or, instead of an armature, fix the cutting/sanding tools on a table, and rotate the foam against it by using a simple pivot.
I already have the extruded blue Dow styrofoam, which then entails something like StyroSpray as a chemical barrier to keep the inexpensive polyester resin from eating* the foam, or else have to go with 3 X as expen$ive epoxy. With StyroSpray, could use cheap polyester resin.
Otoh, if I went with polyurethane foam, I could not hotwire it (toxic fumes) so sanding/shaping would be messier, but then could apply cheap polyester resin and fiberglass without fear of chemically eating the foam. And, I'd have a nice impact absorbent foam pillow in the nose, easily carved for cooling ducts, etc..
Pros and cons of each method. Another post about the Lithuanian guy says go with polyurethane from the getgo.
Got suggestions or advice?
*Cheap polyester resin is about as strong as epoxy when cured at room temperature, but eats styrofoam and is OK with polyurethane foam. Epoxy won't eat styrofoam, but costs 3 x as much as polyester resin. This is a non-structural part, so strength is not a big deal.