The other way to make toroids

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Original poster: "Wim Bosma" <wbosma@xxxxxxxxxxx>

Hello Jerry, If this prescription is overly long, you may snip in it. I 
also attach two small pictures of toroids in the process of making. Regards 
and keep up the good work!  Willem.

Hello all,
I have made several toroids from plastic dryer duct. Its inside stiffener 
is a steel spiral. With a wire cutter you can snip it. Form a toroid by 
sewing both ends together. Then make a styrofoam disc, the size of the 
inner diameter of the toroid to be, about 1 to 2 inches thick and hollow 
the circumference a bit to fit the diameter of the ducting. Now you glue 
(epoxy or woodglue) upon it two thin discs of plywood (or aluminium) to 
make a stiff sandwich. You can stretch the formed toroid so it slips over 
the sandwiched styrofoam disc and stays in place. Try to stretch so that 
the formed outer diameter is as smooth as possible. Now comes the messy 
part... Tear newspapers to shreds and make paperpulp by boiling the 
shredded mass with water while stirring. After having a smooth paste, 
strain the excess water and stir some woodglue thru the paste. You can add 
fine woodmill to this paste. Now apply this paste to one side of the 
toroid, omitting the flat inner surface, forming a smooth surface and let 
it dry somewhat. Then turn over and prepare the other halve. After drying 
you can correct mistakes with another or smoother layer with more sawdust 
in it. Also you can use some filler from a paint store. After drying, sand 
protruding little coarsenesses away and apply a coating of some lacquer or 
Krylon. Now get a roll of aluminium repair tape that has a protective layer 
on the sticky side and cut off  lengths equal to the circumference of the 
ducting and a little bit more. With a Stanley knife cut the straps 
lengthwise in two so you get the double number of straps with half the 
width. The smaller the width, the less trouble in wiping away 
wrinkles...Place straps carefully and symmetrically with respect to the two 
sides, with a small overlap on the outside of the toroid. Press down gently 
and then with a smooth flat wooden spatel flatten out the wrinkles. 
Aluminium tape deforms easily so you should end up without wrinkles...The 
last thing to do is glue aluminium discs on the flat sides that contact the 
repairstrips where they join and overlap each other.
Regards, Willem,  PA0TW

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