I just saw an add for a new cyrnopoxy glue that is both gap filling and multi-surface, including that plastic that pop bottles are made of. Here's the link.
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If you go to the home page and insert the code PRI 04 you can get the sample kit for $6.99 plus $5.00 shipping. I just ordered it and will report back when I try it. Id does look though like it will be great for mating fins to plastic or for converting old pop bottles to rocket frames. Any way, I haven't posted here in a bit and thought I'd return with something useful. Jerry, drop me a line off board and lets talk about some motors for the memorial weekend launch out at El Mirage.