Toroid made easy

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Original poster: gary350@xxxxxxxxxxxxx 

I cut 2 pieces of .040" flat steel into a donut shape.  Donut is 20" 
outside diameter with a 6" diameter hole.  Metal plates are welded 
together along the outside and inside edge only.  A very small pipe 
fitting is welded to the surface of 1 sheet of metal near the 
center.  A 5 lb. bag of charcoal is ignited and given enough time to 
turn the 2 metal plates red hot.  Air is slowly blown into the 
fitting and the red hot metal is blown up like a balloon.  The flat 
metal will blow up into a toroid shape it is sorta like blowing up a 
car tire innertube.  Let it cool.  Grind the welds smooth and reweld 
if needed to make it smooth.  You can also do the same thing to make 
a sphere.   I did the same thing with two 20" circles no donut shape 
this time it made a very nice sphere.   It only takes a few minutes 
for the metal to turn red hot so the charcoal is basically 
wasted.  It would be good to make about a dozen toroid and sphere 
parts get them all welded together and heat them red hot one by one 
it would not be so wasteful on charcoal.  I have not tried any really 
large ones yet but I see no reason someone couldn't cut out some 48" 
donuts shapes to make a large toroid.  When the metal blows up like a 
balloon the outside diameter gets smaller.  You can get a 98% 
accurate idea of the actual size by bending a sheet of paper into a 
radius to see how large your finished balloon shape toroid will be.

Gary Weaver