With all the experimentation done trying to get the 4" coil to throw out the
longest arcs possible, I've ended up with close to a dozen different toroids.
I've been able to make them quickly when needed, and here's how I do it.
From my local dollar store, I've purchased 8" and 9" pie pans. Not the aluminum
foil type, but the type that are thick like sheet metal. I've also purchased 12"
deep dish pizza pans.
I start out by tracing around the bottom of the pan onto a piece of paper, cut out
the circle and fold it in half twice to make a template to mark the center of the pan.
I then take two pans with the bottoms together, and drill a 1/4" hole in the center.
I bolt them together, make sure the pans are evenly lined up, and drill four more holes
2-3 inches from the center.
Short bolts are put through these four holes to hold everything together.
Next, I'll use either 4" or 6" flexible aluminum duct, form a circle, and tape the ends
together with a single layer of aluminum tape. Gradually, the aluminum duct is expanded until
it will just fit over the pie pans. Then, working around the duct, I gradually compress the tube
until it fits nicely between the two pans. Once this is done, I use a thick bead of hot glue to hold
the aluminum duct to the pie pans.
I use a piece of 1" PVC bolted to the center which is how the toroid will attach to the secondary
coil. How do I hold it in place? It's easy. I cut a piece of 3/4" and a piece of 1/2" PVC about
1/2" long. I cut through the outer edge of each ring. They all fit nicely inside each other now.
Glue the three pieces together, use a 1" washer inside the 1" PVC over the smaller rings and bolt
it all together.
Last, I use a 4-5 inch piece of 22AWG wire, use sandpaper to remove the enamel insulation on each
end and bolt one end of the wire to one of the four outer bolts. The other end of the wire gets a spade
terminal. I use these for easy and quick connections and disconnections of the toroids to the secondary