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-   -   Kryptolite (https://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/4579673-kryptolite.html)

Cross Check 08-03-2006 03:30 PM

Hello All,

I've been lurking here for awhile now. Definatly a group of pilots I would have a great time flying with anytime/anywhere...

On another thread you were wondering about spray foam in a mold. Been there, done that, had to throw out the T-shirt ! hehehe

I fly Maac .25 powered WW2 scale R/C combat and a couple of years ago I was looking for a way to mass produce the rounded wingtips that are common on alot of the WW2 warbirds.

I made plaster molds of the two wingtips which have a semi symetrical airfoil with a bit of reflex in the TE. Used vaselene as mold release. Took a long time for the plaster to dry out.
Got a can of 'high expansion' foam at the local Home Despot ($8 Doah !) and sprayed a small shot in the well vaselened molds. Then covered them with some ply with a hole in it to allow any excess to 'fizz' out. Worked great. Waited two days to make sure it dried/cured enough.

The parts poped out easily. Formed nicely. Cool ! Then reality set in. They were alot heavier than I thought they would be. (The stuff had a fairly thick skin where it hit the mold) It was also quite 'rubbery'. Tried again with a smaller shot. (Not enough to fully form the part) but the results were the same. I tried experimenting filling various pop bottles/etc. but my idea of molding light parts out of spray foam died...especially when the nozzle 'bunged up' with the can still 3/4 full !

I did get some light tips out of the molds. I wire brushed some white foam inside a garbage bag to a 'small Rice Krispy' size. Mixed one part 30min. epoxy with 10/20 parts rubbing alcohol. Mixed together so the foam 'bits' were all wet, then packed it in the mold. Parts turned out light and stiff. But the surface texture needed a few coats of Spackle to fill the voids. Nice light tips but it was more work than just sanding foam tips to shape. Experiments stopped when the plaster molds deteriorated...

Next time you have some extra epoxy mixed, try thinning it way down with rubb alc. then mixing in various densities of crumbled white foam. Mix well until most of the alc. has evaporated. Press it into a margarine container/paper cup. Keep it warm because the alc. slows the epoxy cure time. I call the resulting material 'Kryptolite' Warning ! Do Not use an electric drill and a rotary wire brush to create the foam dust...DOAH ! ! ! HeHeHe

As a segway...one of my several 70's era Cox .049's never ever flip starts the right direction. It seems to know which way the prop is on too ! It is mounted on a 2X2 stick. I use it to blow out/dust my shop...

Take care,
Have fun,
Maac 6437
Unabashed Combat Team

combatpigg 08-03-2006 06:26 PM

RE: Kryptolite
Hi CROSSCHECK, when it's all said and done, it's pretty hard to beat balsa at what we are trying to do. The injection molded polystyrene is another story, those planes turn out pretty light. I guess that is the process to look into. I think SIG sells a liquid foam?

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