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Re: Big Toroids, collective conscious brain storm
Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>
Several different fabrication processes COULD be used for fabricating
toroids, but only a few would be realistic candidates for the
low-volumes of Tesla-coil enthusiasts. Some of these processes are:
1. Roto-molding: this is commonly used to form large, hollow plastic
parts from low-melting point plastics (most commonly low-density
polyethylene). It is a fairly low-volume process used for chemical
tanks, specialty containers, etc.In this process, a split, hollow
metal mold is filled with plastic granules, and then slowly heated
while being "tumbled" omni-directionally. The plastic granules stick
to the inside surface as the tool heats up, and eventually fuse into
a fairly uniform layer. The tool is then cooled, opened to remove the
part, and the process is repeated. Unfortunately, the process is very
energy intensive as the tool must be completely cooled and re-heated
for every part, and therefore the production cycle time per part is
quite high. Also, the tooling itself is large, heavy, and fairly
expensive, and the omni-directional tumbling mechanism is fairly complex.
2. Blow molding: this is another process used for production of
hollow plastic components, and is a high-volume process. In this
process a tubular (hollow) plastic pre-form is heated, a mold closed
around it, and air injected to inflate the pre-form and cause it to
fill the mold. Unfortunately, the tooling is quite expensive, and of
course it takes a very large, very expensive machine to perform the
actual blow-molding process.
3. Vacuum-forming I think the best candidate fabrication process for
toroids in the sizes we are interested in, and in realistic
quantities, is vacuum-forming. In this process, a sheet of
thermoplastic is supported in a frame, and then heated by infra-red
lamps or overhead gas burners until it is quite soft. The frame is
the quickly dropped down over a tool (can be "male" or "female"), and
vacuum quickly applied under the heated plastic sheet. This pulls the
plastic sheet down against the plug (or into the female tool) and the
plastic sheet is now an exact duplicate of the tool's surface. The
plastic cools almost instantly, is removed from the frame, and the
excess plastic "skirt" is trimmed off. A completely hollow part like
a toroid would need to be fabricated from two halves, just like a
spun metal toroid, and joined at the periphery. This process can use
many different thermoplastics of many different thicknesses, possibly
up to 1/8" thick. The tooling can be fabricated from wood, plaster,
or you could use a spun-aluminum toroid sitting in a wood "nest" so
that only the top half of the toroid is sticking out. Of course this
takes a fairly large machine, but it is quite simple and
(theoretically) could be home-made using aluminum or steel
angle-iron, banks of infra-red heating lamps, and a "cheap" vane-type
vacuum pump along with a big vacuum reservoir.
A good friend of mine has a large vacuum-forming system that is used
primarily to form aircraft parts (interior panels, etc), and I have
watched this system in use over the years fabricating many different
types and sizes of parts from different types of plastic sheet.
4. Yet another process that could be used is vacuum-bagging. This is
somewhat similar to vacuum forming, can use the same type of simple
home-made tooling, can produce very strong composite parts
(fiberglass, Kevlar, carbon-fiber, etc), but is quite labor
intensive. In this process, a male or female tool is made, coated
with mold release wax, and the layers of composite material are
draped over the tool and carefully hand-worked into place with rubber
squeegees, etc to eliminate all wrinkles or voids. Usually, pre-preg
material is used, which is fiberglass/Kevlar/carbon fiber already
impregnated with resin. Less expensive but more labor-intensive is to
start with dry cloth, and pour on the catalyzed resin as the layers
of cloth are added. After much hand work to get the composite
material into intimate contact with the tool, a piece of plastic film
is draped over the part, clamped down and sealed around the outside
of the tool, and a vacuum is pulled under the film. This allows
atmospheric pressure (14.7 PSI) to press the composite material into
or against the tool. You can see that even a relatively small part
can have hundreds of pounds of force applied to it. Pre-preg material
is the oven-baked under vacuum to cure it, while catalyzed resins are
allowed to cure at room temperature.
This process is extremely simple from a tooling aspect, but is very
labor intensive and really requires a lot of experience to get good
results. It is as much an "art" as technology.
I have talked to my friend previously about forming some prototype
toroids using either his vacuum-forming or vacuum-bagging setup, but
just have not had the time to follow up. Some of his vacuum-bagged
aircraft parts have to withstand lightning-strike testing, with a
fairly high level of electrical conductivity, so I'll check to see
what the material options are. It would be very nice to see a
lightweight, absolutely dent-proof, reasonably-priced black
carbon-fiber composite toroid that was conductive enough for Tesla
coil topload use without requiring an external conductive coating. Or
a vacuum-formed ABS or polycarbonate toroid that was equally-dent
proof, either covered with aluminum tape or sprayed with conductive
nickel-based EMI shielding paint.
Regards,
Scott Hanson
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, September 12, 2006 10:40 AM
Subject: RE: Big Toroids, collective conscious brain storm
Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>
-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Tuesday, September 12, 2006 7:35 AM
Hello all,
Lets use the List group consensus to brain storm a way to make an economical
large toroid within reasonable effort that is strong, light, and smooth
enough to do the Saint Vitas Dance.
(SNIP)
Ideas folks?
Jim Mora
"Better Living through Science"
To: tesla@xxxxxxxxxx
Subject: Re: Big Toroids
Original poster: Gomez Addams <gomezaddams@xxxxxxxxx>
<snip>