38 MM Saucer Questions

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Well-Known Member
Jan 19, 2009
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I'm planning to build a new saucer with a 38 mm MMT out of the same foam I used for the 54 mm saucer. Instead of 2 oz fiberglass as with the 54 mm, I'm thinking of using cotton cloth. I already epoxied some to both sides of a piece of scrap foam and it turned out to be the perfect material, because when I bend the foam, the cotton doesn't crack like fiberglass does. This is exactly what I need my saucer to do, bend without cracking. My concern is that cotton can be flammable. If it's saturated with epoxy, it won't catch fire will it? Does anyone know?

If the cotton cloth is saturated with epoxy, by the time the cotton cloth burns the epoxy should also be burning.

So the real question is "will there be enough heat to set your epoxy on fire?"

I'm thinking 'not likely'.
That is my thinking also. I need flexibility and cotton fits the bill perfectly.

Not worried, just wondered if there was any cause for concern.

Epoxies are not usually very heat-tolerant. (Link.) Most are only rated to a maximum of about 200°F. What part of your saucer would be exposed to high heat? Could you tweak the design a little bit to minimize that? The duration of the exposure to high heat matters, though. A good solid layer can withstand very brief exposure to higher heat levels. There are "high temp" epoxies that are rated to 400-450°F, and J-B Weld claims to withstand up to 500°F. I think that it is safe to assume that the exhaust plume of a 38mm motor is a great deal higher than that, as is the heat generated by the ejection charge.