Re: blue foam & cutting it

[Richard Riley]

On Sat, 22 Nov 2003 09:01:09 -0000, "karel adams"
> wrote:

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

It is absolutely NOT polyurethane. Polyurethane will release cyanide
gas if you try to hot wire it. DON'T.

It is Polystyrene foam, trade name Styrofoam by Dow chemical. The
form usually used in homebuilding is PI (Pipe Insulation) Billets, or
FB (Fabrication Billet) or BB (Bouyancy Billets), made by Dow. The BB
is a little ligher and weaker than the PI or FB, which are the same
thing. The PI's come in 8x16x104 inch blocks, or, lately, 10x20x104.

Don't use white EPB (Expanded Polystyrene Bead) board, often sold for
insulation, or used to make molded foam things like cheap ice chests.
You can recognise it because if you break it, it looks like it's made
from thousands of tiny round beads fused together. That's exactly
what it is. It's chemically the same, and you can hot wire it, but
it's not nearly as strong in flex or tension.

Here are a couple of halfway decent primmers on hotwiring
http://www.info-central.org/construction_hotwire.shtml
http://www.spacemodeling.org/new/how_to/Foam_Cutter.htm

Note - you don't have to use nichrome wire. I've used .020 stainless
safety wire, and titanium MIG wire with good results.

[Lpmcatee356]

>Thank you! That was as extensive an answer as one could wish for!
>I have found the local importer for Dow and sent them e-mail...
>Karel
>Hingene (BE)

I don't know what the situation is like in your country, but here in the USA we
don't tell the Dow rep that we are going to use the foam for airplanes. If we
do they won't sell it to us.

I build lots of boat docks and boats <G>

[Nathan Young]

"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

[Cy Galley]

I thought there was an outlet in England.

"karel adams" > wrote in message
...
>
> "Nathan Young" > schreef in bericht
> m...
> > "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.
>
> Thank you for the detailed description.
> I'm afraid you don't realise I'm in Europe
> (Belgium, more specifically)
> and aircraft homebuilding is far from general here.
> To my knowledge, we don't have an equivalent
> for Aircraft Spruce in Europe - if there is I'll be glad to know!
> So both equipment and knowledgeable people
> are rather scarce though I did manage to
> localise a group of homebuilders at a field some 40 miles off.
>
> OTOH controlling the heating current will not be over tough
> as work in electronics - I'll find some nice appropriate device
> and if I can't find one I'll build one!
>
> KA
>
>

[Marvin Barnard]

For polystyrene foam, I tried the hot wire method and decided it was
easier just cutting with a hand saw and a knife.

[Morgans]

"Marvin Barnard" > wrote in message
...
> For polystyrene foam, I tried the hot wire method and decided it was
> easier just cutting with a hand saw and a knife.

Not too good for following exact templates, on a long section. Hot wires
are a pain, unless they are set up and used correctly.
--
Jim in NC

[Nathan Young]

"karel adams" > wrote in message >...
> "Nathan Young" > schreef in bericht
> m...
> > "karel adams" > wrote in message
> >...
>
> Thank you for the detailed description.
> I'm afraid you don't realise I'm in Europe
> (Belgium, more specifically)
> and aircraft homebuilding is far from general here.
> To my knowledge, we don't have an equivalent
> for Aircraft Spruce in Europe - if there is I'll be glad to know!
> So both equipment and knowledgeable people
> are rather scarce though I did manage to
> localise a group of homebuilders at a field some 40 miles off.
>
> OTOH controlling the heating current will not be over tough
> as work in electronics - I'll find some nice appropriate device
> and if I can't find one I'll build one!

Karel,

Aicraft Spruce has a European store:
http://www.aircraftspruce.com/index.php

The EAA website lists EAA chapter 664 as located in the Netherlands.
http://www.eaa.org/chapter/chapter_locator.html

Good luck!
-Nathan