Re: Foam-core Toroids

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Make it yourself..  Buy a big block of styrofoam (or several smaller ones).
 I'd use blue or green foam that has smaller cells than the white
styrofoam.  Get an electric carving knife and go to it and rough it out. (a
drywall saw also works well)  Then, make yourself a cardboard or plywood
template of the profile you want (I'd go with cardboard, but plywood is
more durable.  Now use a "surform" or a very coarse rasp to get closer to
the shape.  Finish it with sandpaper.  Bondo or spackle if you want a real
smooth  finish.

A center pivot for the template will insure that it's symmetrically round. 
A piece of pipe on the template and a smaller piece of pipe run through the
foam works well.

The other approach is to build it up from something smaller (roughed in
with sawing) and then with plaster of paris or bondo glopped on and
smoothed to shape by spinning the template. Sand for the final finish (This
works real well for making a female mold, by the way, use burlap and lumber
under the plaster.).

Big warning: the foam dust/grit that you sand off is terribly irritating if
you get little particles in your eyes (much worse than sawdust)...... Watch
which way the wind is blowing when you work with the stuff...

----------
> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Foam-core Toroids
> Date: Sunday, September 10, 2000 10:43 AM
> 
> Original poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com> 
> 
> While there is nothing that looks as nice as a professionally spun
toroid,
> consider the agony you would feel if and when it fell off the top of your
> coil and became permanently dented.  I think most of us that have made
> toroids out of corrugated aluminum duct have eventually had them dented
from
> these sorts of mishaps.
> 
> I recently tried an experiment to improve upon the durability of
home-made
> toroids.  I attempted to fill my 6" x 22" Al duct toroid with a
polyurethane
> foam.  This stuff cures to a fairly rigid high density material.  The
stuff
> I used is called "Great Stuff", at Home Depot, for $3.97 a 12 oz can (not
to
> be confused with a latex-based product also sold there).  
> 
> I drained two cans of the stuff and it appears that another 1-2 cans are
> still needed to completely fill it.  I would recommend that anyone
> attempting this have more cans than necessary on hand so that it can be
> filled in one operation, rather than on successive days, with a portion
of
> the filling hardened, then filling more.  I was initially concerned that
the
> foam wouldn't cure being in an air-tight container.  The can said that to
> ensure curing in enclosed spaces, to sprinkle some water, so I squirted a
> couple oz. of water into the toroid prior to foam injection.  It turns
out
> that there is no problem with the foam curing, it hardened just fine.
> 
> The resulting foam core toroid is now more dent-resistant than a
non-filled
> one, but the density of the Great Stuff foam is still less than what I
would
> like it to be to render the toroid totally dent-proof.
> 
> What I would REALLY like to find is a vendor who can supply a nice smooth
> styrofoam toroid, ready for me to cover with aluminum tape.  I think the
> density and light weight of this construction would make it very
resistant
> to denting, and hopefully such a foam toroid could be bought for far less
> than a spun metal toroid.
> 
> I'm interested only in sizes larger than my 6" x 22" so life preserver
cores
> don't help.  Any thoughts on whether such a styrofoam core could be
> custom-made for a nominal fee?
> 
> Regards, Gary Lau
> Waltham, MA USA
> 
> 
>