"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