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Re: [PSUBS-MAILIST] alternative dome forming




Alan,

I wonder if you've looked at, or discussed with your fabricator, a vacuum mold as opposed to blowing the dome.

Jon


Alan James wrote:
Hi Vance & Frank,
I was quoting from "Stachiw" page 13 where as you say Vance they had 4" thick cast acrylic sheets that they were forming the segments from, but Stachiw then looked to cast hemispheres to go thicker. I should have said the segmented
domes were superceded rather than abandoned.
Frank, maybe Greg could wade in on this if he's about, he's the expert. However I'll explain my idea a bit more. You start off with a 100mm thick acrylic slab & cut a ring out that slightly exceeds the diameter & thickness of the dome you require. Then another slightly smaller in diameter & stack it on top & repeat again till you have the desired dimentions of your dome able to be carved out of this crude block; then glue it together, anneal, machine & polish to a perfect sphere and give it a a final annealing. This way would waste a lot of acrylic & a better way would possibly be to form each ring in 2 segments thus utalizing the acrylic block a lot more efficiently. I'm picking that you could make a dome with a 3000ft plus crush depth for under $2000- NZ & get it manufactured locally. The best price I've seen so far for a cast dome would be $5000- plus to land in NZ. One design criteria would be that you don't put any of the joins at eye level. Re the blowing of the domes; I could only find one plastics manufacturer in NZ that would take on blowing a dome 25mm thick (have now upped it to 35mm) & he's struggling. Apparently there's a lot of pressure involved. When I cooked some acrylic I was surprized at how rubbery & firm it was at
the forming temperatures.
Alan




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