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Critter
10-14-2007, 12:02 PM
Building an emergency rudder? After my abortive attempt to build a foam and glass blade for the last Longpac, I have a nearly full 5 gallon can of isophallic -- sorry, make that isophthalic -- polyester resin from Tap Plastics, and an appropriate quantity of catalyst. Since I don't have any major fiberglass projects coming up (I hope!), somebody else may as well use this stuff while it's fresh.

I also have a quantity of Knytex cloth cut into 78 x 30" pieces, plus a few remainders.

I'd like to get a little money for these materials, but not looking for anywhere near what I paid. Let's talk.

Max

jbarthelmass
10-15-2007, 12:27 PM
Max,

Just curious....are there any lessons learned that you can you share regarding what NOT to do when building out of foam and glass?

Critter
10-16-2007, 08:49 AM
Ummm ... basically, don't procrastinate so that you don't have time to do things right.

I went up to Svendsen's on a Saturday to get a piece of Divinycell for the core, only to find that with the shop closed they had no way to cut it. Thinking I had to get the blade pretty well built that weekend, I decided to go with Styrofoam building insulation. Yes, I know it's not right, but I figured it would be better than nothing. But for some reason, I couldn't even find Styrofoam, and I ended up with a plank of some other foam that was even weaker than Styrofoam and smelled a bit like dead animals. Not being a complete idiot, I found a piece of 2 x 3 rectangular aluminum tubing, cut a slot in the foam, and epoxied the tube into it to give the blade a little backbone. I got the blade nicely shaped and suspended it between two tables. When I gently laid the first piece of wetted out cloth on it, it broke at the end of the aluminum reinforcement. I think I said "Darn!" or something like that.

That's when I changed course and went to the wood and aluminum structure that I described in the other thread.

tiger beetle
10-16-2007, 03:16 PM
Thinking I had to get the blade pretty well built that weekend, I decided to go with Styrofoam building insulation. Yes, I know it's not right, but I figured it would be better than nothing.
Were you using polyester resins on the foam? Polyester resins are incompatible with styrene-based products (e.g., styrofoam, blue board insulating foam) - the foams will effectively 'melt' as the polystyrene chain molecules that are the basis of the foam are broken up. If you want a really effective demonstration of this, hold a styrofoam cup in your hand and pour acetone or styrene into it - quite exciting!

Epoxy resins do not attack styrofoams. Polyurethane and polyvinylchloride (PVC) foams are compatible with polyester and epoxy resins. (Divinycell is a PVC foam.)

Bottom line is to experiment with the materials before going into full-scale production on a part.

- rob/beetle

Critter
10-17-2007, 09:02 AM
Were you using polyester resins on the foam? Polyester resins are incompatible with styrene-based products (e.g., styrofoam, blue board insulating foam)
I didn't know that. Yes it was polyester resin, but no it wasn't Styrofoam. It was a fine-grained beige foam; I don't recall the name. It clearly broke from the weight of the cloth, not because of a chemical reaction. Really feeble stuff, it's good I didn't get any farther with it.