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Re: [PSUBS-MAILIST] alternative dome forming
Hi Jon,
After 10 &1/2 months I've discussed a lot of things with him.
I think he had a go at vacuum molding. He had problems in that the ring
retaining the acrylic sheet was a bit on the thin side. Then when he beefed
it up the clamps weren't retaining it so he's bolting it all down. He was
talking
about a combination of vacuum & blow molding or vacuum & pressing the
centre.
I'm not sure what he's up to now but assures me it won't be long.
He is respected within his profession & has done a lot of large aquariums.
However I'm looking at my alternatives.
Alan
----- Original Message -----
From: "Jon Wallace" <jonw@psubs.org>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, April 06, 2010 5:28 PM
Subject: 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domes were superceded rather than abandoned.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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