Alan & Brian, Our resident expert, Greg Cottrell gave an excellent presentation on this subject at the Raystown PSUB Conference a few years ago. He has accomplished some remarkable things with acrylics and noted that casting a dome was not a simple matter, fraught with opportunities for failure. He described three methods if my memory serves me right. From his presentations it was the audience’s opinion that it should be left to professionals when it comes to casting a dome. Depending on the casting, the heat generated if not compensated for, could result in an intense fire in the mold. R/Jay Resepectfully, Jay K. Jeffries Andros Is., Bahamas Save the whales, collect the whole set. From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Alan James Hi Brian, Brent & I have been looking at this off site recently. I spent a lot of time looking for an unpolemerized methyl methacrylate with a catalyst. wich is the raw materials they start with to make the sheets. Eventually I found some with a plastics guy who has blown domes for me. He bought a drum of it & said it was very hard to work with. With the domes there is a very controlled heating process in pressurized ovens. Out gassing in the setting process forms bubbles that attach to the sides of the molds and are hard to remove. Hugh went over to Stanley plastics & saw the process. He said they over compensate the dimentions to allow for the outer faces to be taken back beyond the " bubble layer ". I've mucked around with polyester casting resin for a while & large castings are a bit of an art. They can take days to set, & there is a relationship between temperature & amount of catalyst. If you get it wrong the mold cracks or the materials too soft. Hope someone else comments, it would be interesting to learn more. Alan |