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RE: [TCML] DIY dent-proof Toroids

I tried it a few years back and had troubles, though I think I only posted
the disaster story of it on the UK list. It did indeed leave voids as
mentioned, and when cut open later it did not seem to have expanded inside
as much as I would have expected. At the time I used a slightly more
flexible ducting than the usual dryer duct I use, so it really did need that
extra rigid support of the foam inside. The result mess went in to bin!
However I suspect the foam was not up to par, (not the operator) as I have
been told that it can be capable of distorting a plastic door or window
frame with the pressure it exerts, how true that is I don't know. But if
true, it could serve the purpose we want, apart from the possibility of
voids occurring still.
At the moment I am making a 18 x 4 inch to sit underneath my usual 34 x 8
inch (in an effort to divert primary strikes) and despite the messy carnage
that followed my last attempt, I am again considering 'injecting' the thing
with foam. 
I already have the Alu ducting covered and smoothed with filler though, so I
am wondering that if the foam expansion actually worked this time, it may
crack the existing filler, hence my apprehension.
Were someone to do it I think they would need (possibly) three 120 degree
injection points, to be sure of getting to all of the inside of a toroid
shape though.
A dummy run with some spare duct would be the best approach before you try
Dave, allowing an autopsy afterwards.

Marks idea that I posted on the site has the advantage that you can see the
finished core before it's covered. The injection method being discussed
here, means it's a "fingers crossed" situation - only finding out the answer
when you bump into something!

Downside to using foam: Don't even think of trying it without disposable
gloves on.

Phil Tuck


-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of David Rieben
Sent: 27 May 2013 13:15
To: Tesla Coil Mailing List
Subject: Re: [TCML] DIY dent-proof Toroids

First of all, wishing a great Memorial Day to all the fellow US based
coilers. Now to my point ;^) I've been following this "DIY dent-proof
toroid" thread and I was just wondering.... If you already have the typical
"dryer duct" type toroid, could you also not carefully drill a few holes in
it in an inconspicuous location (say along the top and near its minor
diameter radius) that are just large enough to allow the nozzle of one of
those urethane foam canisters to be inserted and backfill the toroid with
the foam in this manner? It seems IIRC that this may have been lightly
mentioned in a previous post and someone had cautioned the possibilty of the
foam expanding unevenly and causing unsightly "lumpiness".? Reason I'm
asking is that I already have a huge 12x56 (inch) topload on my large coil
and I have already put a good deal of blood sweat and tears into its
construction. It was based off some industrial quality 12" diameter flexible
duct that was
 purchased from McMaster-Carr. I ended up cutting strips of aluminum
flashing and covering the duct surface with the flashing. Adding enough
flashing to completely cover the exterior surface of the ducting ended up
adding significantly to the total weight, too ;^o (Estimate 30 - 40 lbs
total weight now). This has "helped" in dent resistance but it could
still be "better". I was wondering if it would be safe to the long term
outcome of my big topload if I were to backfill it with that urethane foam?
How would one determine how much foam was "enough"? Would like to glean
suggestions from the collective advice of this list before investing in 2
dozen cans of urethane foam and/or possibly ruining my huge work of art. :^/

From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: tesla@xxxxxxxxxx 
Sent: Sunday, May 26, 2013 9:14 AM
Subject: Re: [TCML] DIY dent-proof Toroids

On 5/26/13 7:00 AM, Dave Halliday wrote:
> And these would be the people to do it -- I live about 30 miles North.
> http://www.janicki.com/index.php/5-axis-milling.html
I don't know if that one is big enough for the toroid I have in mind.. 
Maybe in sections?


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