Re: Alternate sources for large secondary coil forms (fwd)

---------- Forwarded message ----------
Date: Tue, 7 Jul 1998 08:17:00 -0600
From: "D.C. Cox" <DR.RESONANCE-at-next-wave-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Alternate sources for large secondary coil forms (fwd)

to: Clay & Jim

PVC pipe as used in the water pipe & sewer materials construction industry
comes in 3 common grades.  The schedule 40 is a medium wall pipe and is
suitable for most Tesla oscillators.  The schedule 80 is very thick walled
for high water pressure and is usually too heavy for Tesla coil secondary
construction.  The best type to use is the thinnest walled pipe known as
SDR (stands for "sewer & drain").  SDR is thin walled, very light, and is
usually green in color.  It makes for light coilforms and is great if you
don't try to sit on it.  Thorough cleaning is necessary both inside and
outside and 2-3 coats of glyptal is applied before winding.  Allow
overnight to dry between each coat.  These forms work up to 1,000,000 volts
(8-9 t. sparks), and after that it is best to use Extren (structural
fiberglass) which is expensive but if you are building a monster coil this
is no surprise.


> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Alternate sources for large secondary coil forms (fwd)
> Date: Monday, July 06, 1998 10:47 PM
> ---------- Forwarded message ----------
> Date: Mon, 6 Jul 1998 00:07:30 -0700
> From: Bill Noble <william_b_noble-at-email.msn-dot-com>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Alternate sources for large secondary coil forms
> why not roll your own?? wrap your choice of material around something of
> right diameter - for example, roll some vinyl around a pipe and you can
> a vinyl form - remove the pipe of course after gluing the vinyl.
> -----Original Message-----
> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Date: Friday, July 03, 1998 11:43 PM
> Subject: Alternate sources for large secondary coil forms
> >
> >
> >----------
> >From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
> >Sent:  Friday, July 03, 1998 10:27 AM
> >To:  Tesla List
> >Subject:  Alternate sources for large secondary coil forms
> >
> >
> >> If no one is aware of probs with HDPE coilforms, I suggest that
> >> those of you looking for larger coilforms try commercial pipe shops
> >> specializing in sewer mains...that's where I found some. 
> >> I'm still looking for an appropriate scrap (it comes in 40 foot
> >lengths...
> >> :-(
> >>
> >> Also tends to be thick-walled and very heavy; one example of a 20 inch
> >> specimen had a 0.6 inch thick wall, and the guy said it was 16
> >> On this basis, it might be a bit impractical unless one could find
> >thinner
> >> stock.  Anybody out there finding large diameter PVC??
> >>
> >> Clay
> >
> >The thick wall PVC is what you are going to find. Sewer pipes have to be
> >strong enough to withstand the pressure of the soil (ask any civil
> >engineer, there isn't anything called "dirt") that the pipe is buried
> >which essentially determines the strength requirement. Sewer pipes
> >run at atmospheric pressure, so the "bursting strength" requirement is
> >minimal.
> >
> >For a thinner wall tube, a bit of fabrication might be required, but
> >wall polyethylene drums are available. A couple of 50 gal drums  welded
> >is a pain to glue, but easy to weld) together end to end, perhaps after
> >removing the heads. You could make an insert out of 1/8" or 0.100 LDPE
> >strip to use as a coupler.
> >
> >For an even bigger fabrication challenge, but one that would certainly
> >well, why not get a sheet of 0.100 PE and wrap it around a form (like
> >sonotube) and weld the seam. It comes 4 feet wide and 10 feet long, so
> >would need to either lay vertical strips (along the axis of the
> >or spiral it (much like the sonotube is made).
> >
> >And, having just worked with a radome manufacturer (where dielectric
> >properties are very, very important) to spec out a 4 foot diam, 6 foot
> >cylinder, here are some more thoughts. They make radomes a couple of
> >One way is to start with a paper honeycomb cellular core (from Hexcel,
> >instance) which is laminated with fiberglass prepreg layers on the
> >and outside. They vacuum bag it and cure it in an oven. A typical
> >is .030 fiberglass, .100 honeycomb, and .030 fiberglass. Our 4x6 foot
> >cylinder will weigh about 50-60 pounds and be extremely rigid.
> >
> >Another way is to use foam and laminate the fiberglass over it. The key
> >to get that center layer fairly thick, which gives it strength once you
> >the inner and outer layers on it.
> >
> >Both of these schemes have very low RF loss (at 13 GHz, the dielectric
> >is down in the hundredths of a dB, so at 1 MHz and lower, it probably
> >an unmeasurably low loss).
> >
> >You could just use a big solid cylinder of foam and then laminate
> >fiberglass over it.
> >
> >Foam is a bit pricey in big blocks suitable for a form, but you might be
> >able to find something. You could glue some 2" thick foam slabs together
> >into a hollow octagon or something, and then turn the outside circular.
> >up sort of a giant lathe (i.e. the same rig you are going to wind the
> >with later) to turn the foam down to a cylinder. Laying up fiberglass
> >particularly difficult. You would want to use a very dry layup to reduce
> >the amount of resin. I would suggest checking out the literature on
> >airplanes with foam fiberglass composites (like the Rutan VariEZ).
> >Companies like Aircraft Spruce and Specialty in Tustin, CA (maybe it is
> >Santa Ana? (714) area code, anyway) sell kits for this, as well as the
> >and stuff.
> >
> >
> >
> >