"karel adams" wrote in message ...
dear all,

what is the blue foam around which composite parts are built?
is it polyurethane? what brand names does it carry in europe?

also, where can i find a description of how to build
an electrically heated cutting wire for the same?

Aircraft Spruce sells a book discussing 'Moldess Composite
Construction'. This book was written by Burt Rutan. They also sell a
'kit' comprised of foam, various fiberglass weaves, and epoxy. I used
this to build a few test wings and learned a lot in the process.
(Including a deep hatred for sanding).

Going from memory... The cutter used in the book is a long strip of
2"x2" with a 1/2" copper pipe snug fit into 1/2" holes in either end
of the 2"x2". A small hole is drilled through the ends of the copper
pipe, the cutting wire is fed through the holes, and looped a few
times around each pipe. Tension is applied to the cutting wire by
rotating the copper pipes (a bit like tensioning a guitar string).

I used a car battery and lightweight jumper cables (from a battery
charger) as the current source. Fasten one of the jumper cables to
the copper pipe on the cutting tool.

A variable resistance needs to be added in the path to control current
and hence the heat in the cutting element. For this, I used another 3
foot section of 2"x2" (attached to the workbench) with a wire strung
between two nails at either end. Connect the other jumper cable to
one end of the wire.

Connect a heavy-duty alligator clip to other copper pipe on the
cutting tool through a length of wire. Attaching the alligator clip
to resistance wire completes the circuit and allows current to flow.
This will cause the both the cutting wire and the resistance wire to
heat. Current can be adjusted by moving the alligator clip in various
locations along the wire.

It is a bit of an art to select the right current for cutting. Too
hot and the foam will melt away, leaving divots and shriveled foam in
the cut. Too cold and the wire will not cut well - which will stretch
the wire and leave a cut that is not even.

Having said this - you can probably purchase a better assembly
(Aircraft Spruce?) than you can build. Or borrow one - talk to your
local EAA chapter - if anyone has built an EZ - then they should have
a foam cutter.

-Nathan