Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hi All,I did something similar on the last 6.25" x 21" toroid I built for a 4.5" coil. I simply bought 6" al flex tubing, formed it into a toroid and joined the two ends with duct tape.
I then bought a couple boxes of "plaster of paris" and a patching mix (made by the same company). I simply made a 50/50 mix of the two (the plaster of paris sets pretty quick, has a very smooth texture, but is more difficult to sand). Thus, mixing the two resulted in a nice smooth hard surface that didn't require OT on the sanding. I simply did 1/2 the toroid one day and the other 1/2 the next (filling in the ridges of the al flex tubing). I spent the next couple of days with the inner area and outer area. When all was dry, I simply sanded it into a smooth toroid.
I then used 2" wide strips of Al foil (contact cement on 1 side) until the entire form was covered. As each strip was installed, I used a large Craftsman socket to smooth each strip. When all was done, the form was smooth to the touch without flaws, unlike other forms I had covered with Al foil. Just using a very smooth form in the first place gets you miles ahead of the game.
I used 2 of those 8" salad bowls in the center, back to back and a small screw to join them at their center. There was just enough air gap (1/2") that tightening the screw pressed the the salad bowls against the inner toroid walls holding it nice and firm for mounting and made an excellent electrical connection to the toroid itself.
It worked out nice and is tough enough for everyday "garage" use (and far less weight than spun aluminum toroids, of which I have).
Although you may "see" lines of the tape in the photos below, you can't feel them. However, even for a toroid with Al foil covering which is perfectly smooth to the touch, the sparks still will break out along the edges of the tape which this particular image captures.
http://www.classictesla.com/photos/ba45/s2847.jpg However, it doesn't affect performance: http://www.classictesla.com/photos/ba45/s2816.jpgSorry I don't know the names of the boxes of mixes I used, but I believe the plaster was in a red box (like 4"x3"x8") and the patching powder was in the exact same box size but of a different color. The boxes were next to each other at ACE Hardware. It's a simple way to make a nice toroid and size really only changes how much compound is needed. I don't remember paying much for the boxes of plaster and patch. It's an economical means of building a nice toroid (granted, not cosmetically ideal, but certainly electrically ideal).
I don't like the copper tubing idea. I've thought that one through over the years and it's just too labor intensive and too expensive.
Take care, Bart Tesla list wrote:
Original poster: "Jim Mora" <jmora@xxxxxxxxxxx> Hi, Suppose a drywall toroid (simple sanding, yet fragile at this stage) was made than coated with epoxy (sprayed)?. This would greatly increase the strength and keep it very smooth. Perhaps Dr Resonance's paint will do the trick? Otherwise the challenge is to coat plastic or something like that and use it as a grounded target to discover the best enduring coating. D.C., can you use your paint as a target? Jim Mora -----Original Message----- From: Tesla list [mailto:tesla@xxxxxxxxxx] Sent: Wednesday, September 13, 2006 5:12 AM To: tesla@xxxxxxxxxx Subject: RE: Big Toroids, collective conscious brain storm Original poster: Yurtle Turtle <yurtle_t@xxxxxxxxx> Years ago, I built a drier duct toroid, and covered it with drywall mud. I got it real smooth, then painted it with a metallic paint. I don't remmeber which kind of paint I used, but it ended up looking more like a crackle tube than a tesla coil. The arcs never really left the toroid, but rather ate away the paint, much the way a CD on a tesla coil does. It was really cool, but may not be what you're after. Has anyone tried using metallic paint on a topload? Adam --- Tesla list <tesla@xxxxxxxxxx> wrote: > Original poster: "Jim Mora" <jmora@xxxxxxxxxxx> > > Terry, > > You did quite a lot of electrostatic modeling. How > important is the actual > complete toroid considering the inside is a flat > plane generally? > > I just got of the phone with a boat fiberglass > repair expert. Suppose we > were to make a large alum duct toriod as usual on a > large flat surface, and > wrap it in fiberglass or yet to be discussed fabric. > They have epoxy spray > guns and could gel coat them for real smoothness and > keep it thin enough to > be unnecessarily too heavy. > > I liked the idea of nickel paint they use on cheaper > plastic PC covers for > RF shielding. Hey it Passes class B or C FCC, should > work great. Anybody got > a cover or some of this paint to use as a target for > testing? > > Jim Mora >