Re: Toroid Design

In a message dated 12/22/98 11:17:06 PM Pacific Standard Time,
tesla-at-pupman-dot-com writes:

 There's several different kinds of ducting material out there. One kind
 (which sounds like the material you used on your dryer) has a spiral of
 springy wire with either a metalized mylar or very thin aluminum foil
 wrapped around it, and an 8' length is scrunched down to abot 4" long.
 You DON'T want this stuff. The right material is more like a thinwall
 (0.005"?) aluminum bellows that's fairly stiff and is shipped somewhat
 compressed. The 8" diameter material I purchased was about 2-2.5 feet
 long, but would stretch out to about 7-8 feet. It will dent if you poke
 it hard enough or drop the toroid, but otherwise is pretty robust. 
 It's also very easy material to work with. I used a small piece of
 rolled galvanized steel (also in the heating and ventillation section)
 about 3" wide to fit tightly in an open end, putting it about 1/2 way in
 and then taping it in place with aluminum tape. I slipped the end of the
 next piece of ducting over the 1 1/2" that stuck out of the other duct,
 and taped the joint, and then carefully smoothed out any protrusions.
 I used a couple of 14" pizza pans spaced about 3" apart via three 2" PVC
 pipes for my center, but for a larger center I'd use the same approach
 that Chuck Curran recommended by using some 1" aluminim foil covered
 insulation board used in home construction. It's cheap and light weight.
 Just remember to make good electrical contact between both the top and
 bottom foil layers and the toroid. You'll nd up with a toroid that's
 light wieght, works great, and is very inexpensive. Heating and
 ventillation suppliers should carry the ducting material in up to 18"
 Good luck, Ed, and let us all know how the bigger toroid works!
 -- Bert --


Ok, thanks, this is the material that I was thinking of.  It does sound like a
quick and relatively inexpensive method to make a large toroid.  My old method
of covering every square inch with the aluminum tape would be expensive for a
toroid this large - it would require many rolls of tape.  I will make one as
you have described.  This one inch thick insulating board with aluminum on
both sides, does this stuff come in 4 x 8 foot sheets?

It should have this complete in a couple of weeks, as time allows.  It will be
a few months before I can test it however since I can only run the coil

Ed Sonderman