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Toroid construction and questions

Subject: 
        Toroid construction and questions
  Date: 
        Sun, 6 Apr 1997 13:47:43 -0400 (EDT)
  From: 
        FutureT-at-aol-dot-com
    To: 
        tesla-at-pupman-dot-com


All,

I just built a 5" x 20" flexible aluminum dryer duct toroid.  Recently
someone posted the nice idea of using monofilament fishing line to sew
the
ends of the ducting together.  Well, I didn't have any fishing line, but
this
gave me the idea of using bus wire "staples" to tack the ends together.
  First, I trimmed the ends which had been damaged by handling, by
cutting
away two of the "corrugations" on each end.  Normally there are four
corrugations between flat seamed areas; by having two corrugations at
each
end, there were again four "together" when the ends are stapled.  

Next I used a sharp dental pick to poke small holes sideways through the
two
end corrugations.  Eight sets of 2 holes were created at one end of the
duct,
and the 2 holes in each set are 1/4" apart.  Bend the duct into the
proper
toroid shape, then poke a matching pair of holes on the "un-poked" end
of the
duct.  Use a needle nose pliers to bend a 6" long piece of #22 tinned
copper
bus wire, into a hairpin shape.  Carefully thread the ends of the
"hairpin"
through the edge of the corrugations on one end of the duct, and then
into
the mating holes (after poking them) on the other mating end of the
duct.
 Pull the duct ends together and bend the bus wire ends flat against the
corrugation and against each other.  Snip off the excess wire, so that
only
the overlapping sections of the bus wire remain, then solder them
together.
  When this is done correctly, the soldered connection, and also the
opposite
unsoldered end of the hairpin will lie within the seam channel between
sets
of corrugations, so that nothing projects above the level of the
corrugation
surface.  Continue to install these hairpin staples around the toroid
joint
until all 8 (or so) have been installed, and toroid ends are firmly held
together.   If done neatly, the joint hardly shows, and sparks will not
preferentially stream from the joint.  

As an aside, I noticed that my two old flexible aluminum duct toroids
(one
smaller and one larger) seem to be formed from a duller and heavier
gauge of
aluminum.  Does anyone have the true "dope" on these ducts?  Is it
simply a
variation between brands, or are the heavier ones used for some other
purpose
such as air conditioning, etc?  Is there a prefered source of these
items,
plumbing supply, heating and air conditioner supply, etc?

I just spoke to Lou Balint, who uses an internal coupler and hot glue to
fasten together his toroid ends, this is probably a lot easier than the
method I described above. 

Toroids for today and tomorrow,

John Freau