On Mon, 30 Jun 2003 22:53:08 +0100, "Jan Møller"
(fjern xx) wrote:

Looking for a source of Lexan or similar material that the supplier can form
into a dome to be used as a lookout on my Open 40' singlehander. Radius is
21 cm.
Have tried various places and Google but to no avail.
Thanks in advance for any help and hints
Regards
Jan


There is a vigorous cottage industry engaged in forming cockpit
transparencies for light aircraft. Homebuilders will often make a ply
crate with an internal electric heater to allow a flat to be heated to
its spaghetti temperature, whereon they place it gently over a felt
covered (even greased) form, and gently press it down in contact.
This is not everybody's cup of tea. There is at least one shop that
does nothing but transparencies of this kind, and does them
perfectly. I have not kept contact details, but I could suggest you
readdress the question to rec.aviation.homebuilt where doubtless
someone would have the address on file.

Brian Whatcott Altus OK

Jan Møller says:

Looking for a source of Lexan or similar material that the supplier can form
into a dome to be used as a lookout on my Open 40' singlehander.

Jan,
Good to hear from you. I'll look around and see what I can find.

Steve
Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm

Though I am not speaking from personal experience, I know that people
have often taken two even three shots at forming their windshields
free of ripples and other defects. Still, a surprising proportion do
make an optically satisfactory transparency.

Brian

On Tue, 01 Jul 2003 00:43:08 GMT, "Karin Conover-Lewis"
wrote:

It strikes me that it would be difficult to maintain optical clarity while
forming a dome in this manner -- any thoughts?

"Jan Møller" (fjern xx) writes:

Looking for a source of Lexan or similar material that the supplier can form
into a dome to be used as a lookout on my Open 40' singlehander. Radius is
21 cm.
Have tried various places and Google but to no avail.
Thanks in advance for any help and hints

If you get a solution, could you post it back here? Especially if you
find a shop that can custom-make these things.

Thanks.

--
(Simon Brooke) http://www.jasmine.org.uk/~simon/

to err is human, to lisp divine
;; attributed to Kim Philby, oddly enough.

"Jan Møller" (fjern xx) wrote in message . dk...
Looking for a source of Lexan or similar material that the supplier can form
into a dome to be used as a lookout on my Open 40' singlehander. Radius is
21 cm.
Have tried various places and Google but to no avail.
Thanks in advance for any help and hints
Regards
Jan

I used to work in a plastics forming shop where we did such things.
Polycarbonate (Lexan) has a high deformation temperature and low
scratch resistance. PMMA (commonly called acrylic, Lucite, etc) has
higher optical clarity, scratch resistance, and lower deform temp, so
is preferred for forming. The high impact resistance of polycarbonate
MAY be essential for some applications. In any case, you'll want to
spec a UV resistant grade of material.

For either material, vacuum forming without a mold is the way to go.
The material is held in a rigid frame and heated to a temperature
where it is fairly soft. Then the air on the lower side is evacuated
in a controlled manner until the dome reaches the desired height
(depth?). We used a photoelectric switch to shut off the vacuum valve
when the dome broke its beam. It doesn't require a high quality
vacuum, but you will need to evacuate a volume, so some sort of
reservoir tank is usually needed. The frame material should ideally
be a poor heat conductor and have a polished and radiused edge.

With a little searching, I think that you can probably find a
ready-made source for plastic domes, but it can be fun to try to make
your own.

Paul Mathews

hi
what you need is Macrolon which is avaliable from builders merchants, it
comes in large sheets and many different thicknesses. it is a sandwich of
Lexan ( polycarbonate ) and another plastic. It will not yellow or crack and
is said to be bullet proof. You can also cold fold it with a metal bender
without cracking so has many uses.

richard



"Jan Møller" (fjern xx) wrote in message
k...
Looking for a source of Lexan or similar material that the supplier can
form
into a dome to be used as a lookout on my Open 40' singlehander. Radius is
21 cm.
Have tried various places and Google but to no avail.
Thanks in advance for any help and hints
Regards
Jan

look into building a vacuum form out of wood...
"Brian Whatcott" wrote in message
...
Though I am not speaking from personal experience, I know that people
have often taken two even three shots at forming their windshields
free of ripples and other defects. Still, a surprising proportion do
make an optically satisfactory transparency.

Brian

On Tue, 01 Jul 2003 00:43:08 GMT, "Karin Conover-Lewis"
wrote:

It strikes me that it would be difficult to maintain optical clarity
while
forming a dome in this manner -- any thoughts?