Re: Toroid Building

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "D&M's High Voltage, Inc." <dmshv.davmckin@xxxxxxxxxxx>

List:

When we manufactured toroids, we covered the AL duct with a tape 
(tried various ones, masking, paper, fiberglass cloth).  Masking tape 
and paper tape worked the best.  We then put a thin coat of 
fiberglass over that and sanded it smooth.  Any indentations we 
filled with bondo and sanded smooth. When we applied the bondo, we 
used a spreader to make it as smooth to the surface as possible (any 
bumps just meant more sanding).  If we sanded into the corrugations, 
we would then put another piece of tape over the opening. It takes 
about 6-8 applications of fiberglass to make the surface smooth and 
thick enough to withstand the rolling process and be rugged enough to 
withstand some banging around. We sand down the rough spots between 
each application.  It's important that you make each layer as smooth 
as possible before applying the next layer of fiberglass resin.  Keep 
in mind, it is a very laborious process, and creates an enormous 
amount of fiberglass dust. We used a vacuum attached to a palm sander 
for the sanding process.  We put the fiberglass resin on using 2" 
chip brushes (easily available at ~$0.88 each from Home Depot).  We 
bought boxes of them from Harbor Freight Tools.

The whole key is to get a smooth and even surface as soon as 
possible, and keep it smooth and even - don't put too much fiberglass 
on at a time as it will run!  One thing to also mention - we mixed 
the fiberglass resin very very hot!  We used something on the order 
of 30 drops for approx. 3 ounces of resin (we used 16 oz. cups to put 
it in and it would melt the bottom of the cups when it fully 
cured).  You have approx. 3 minutes of work time the way we mixed it 
(depending on the temperature outside).  When it was cold out, we 
mixed it even slightly hotter ~40 drops / 3 oz.  It would be ready to 
sand within 1/2 to 1 hour.  We also mixed the bondo really hot - same 
approx. working time.  Sometimes we had < 1 minute, we then had to 
back it off a bit.  We would lay them on a couple of pieces of wood 
and then cover the side facing up, once cured, flip it over and do 
the other half.  This did cause a little bit more sanding in the 
middle where the resin met.

Once you have a very smooth surface, then cut the AL foil in strips 
1" wide and long enough to go around the cross section of the toroid 
(~20" long for a 6" diameter cross section).  The tape should 
slightly overlap end to end inside the center of the toroid where the 
center disk goes (do not cut the tape too short!).  Wrap the AL tape 
around the cross section toroid and smooth it down as you apply the 
tape.  Put the next piece so that it slightly covers the previous 
piece, and then after a few say 3 to 6 pieces, roll it smooth using a 
formica roller (handle with a flat roller on one end).  Whatever you 
use, it must roll very easily or you'll just scratch the surface of 
the aluminum tape.

For the center disk, we used aluminum sheet approx. 11 Ga. (depending 
on size of the toroid and what was available at low cost).  We cut 
the disk to fit close to the center (top to bottom) and had to sand 
it down to fit where the toroid wasn't fully circular.  We then used 
short pieces of 1" wide foil approx 1-1/2" long to attach the disk to 
the aluminum tape covered toroid.

We tried plaster of paris for a while, worked pretty good for smaller 
ones, but we went back to the method just described - it was 
difficult to make a smooth surface and to sand smooth and even.  We 
even tried combinations of plaster of paris and fiberglass resin.

For very rugged toroids, we used fiberglass cloth.  More work than 
described above (same process though), but will take an extreme beating.

Best regards,

David L. McKinnon
D&M's High Voltage, Inc.



----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, August 19, 2005 10:55 AM
Subject: Toroid Building


> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi All,
>
> I'm in the process of making a 8x32 inch toroid using the heavy 
> ducting from McMaster-Carr
>
> I have the toroid formed (ends attached) and I plan to mount an AL 
> disc in the center with a little RTV.  I want to fill the 
> corrigations with something that can be easily sanded to make 
> smooth.  I am planning on using PLASTER_of_PARIS for this purpose 
> (done after the center disc is mounted for rigidity).  After sanding 
> smooth, I plan on sealing the plaster with a varnish and then adding 
> AL tape starting and terminating on the AL disc.
>
> Does anyone see a problem with using the plaster??  Grout is maybe 
> another choice for a filler. Ideas welcomed.
>
> Gerry R.