RE: Foam-core Toroids

["LOCKWOOD, Chris J." <clockwood-at-orbeng-dot-com.au> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

With styrofoam, you can shape it very nicely with plaster sanding sheets
(they look like flywire). The beads very rarely pop out this way. You can
use an electric plane to get the rough shape of the curves, then finish with
the flywire.

Heres an idea- how about making a hot-wire jig, using a rigid wire with the
semicircular shape. Refrig tubing with fglass spaghetti insulated nickel
wire inside for the heater element? This could be used to make very neat
styro toroids... Hotwired styro is very smooth.

Another advantage is with the memory of the foam. Polyurethane foam (either
the 2-pack, or pre-formed) has very poor memory- if you dent it, it wont
spring back. Styrofoam is much more springy.

Another advantage is the cost- if you're buying it, styro is HEAPS cheaper.

Using epoxy resin on styrofoam is fine. Styro is also unaffected by
ispopropyl alcohol, (which dissolves epoxy).

Since the styro I'm talking about is very low density- it might need a layer
of fibreglass over the outside, to harden it up a little... I'm going to
give it a try!

Chris


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, September 12, 2000 9:59 PM
To: tesla-at-pupman-dot-com
Subject: RE: Foam-core Toroids


Original poster: "Richard Barton" <richardbarton-at-caving5.freeserve.co.uk> 

Hi
	I believe that stuff you are referring to is Polyurethane, which is
the same stuff that you create with 2-part mixes. This is also petrol-
resistant and resin resistant, unlike Polystyrene, which dissolves very fast
 in contact with petrol and any other petroleum-solvent stuff, and in resin.
You can't make your own Polystyrene. Interestingly enough, they actually
make boat hulls from Polystyrene (I owned one once...), but you get the
option (yes- it's an OPTION!), of buying it clad in resin gel-coat, the
layer
of which is as thin as an egg-shell, and quickly breaks up.... but what
happens
when you sail your boat into a petrol-slick ?
Polyurethane tends to be yellow in colour, and hard.
You find in fridge linings.
 If you scrape it, you get fine dust. Polystyrene is white, and made of
little globules.
If you scrape this, the globules peel away, and you can't get a perfectly
smooth
surface.
						Richard.
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