I noticed one or two postings about 
making toriods using rubber tubes
the problem seems to be that over 
time these always deflate - leaving
a very sad looking toriod.

Following others on the list I made 
my first small toriod using a
plywood disc and foam pipe lagging - 
about two inches diameter
I cut a slit in this to the centre 
and wrapped it round the disc
using wire to hold it in place, 
I then used aluminium tape to cover
it all for an 18" by 2" toriod.

My second toriod uses 4" diameter 
Aluminium ducting - this comes
as a 1 meter long tube that can 
be extended to 3m. I cut two plywood
discs 2 foot diameter and then covered 
one side with aluminium foil -
fixed with wood glue. These board 
were then fixed one inch apart,
using a couple of pieces of wood. I then 
stretched the ducting around this
wheel. (I would fix the plywood discs 
2 inches apart in the next one.
Easier to fit)

I had passed a wire and one of those 
stretchy luggage rack ties through
the ducting to hold it in shape 
(next time I'll use a piece of chain 
so that I can easily alter the tension.

It is fiddly to strech and shape 
the ducting material - two people
would be better.

I had drilled holes though the edges 
of both plywood discs,
about 1/2" in and 6" apart I passed 
wire though the holes and
round the ducting to secure. 
I also used wire to tie the ends
of the ducting together and 
used Al foil to cover over the join,
I soldered the wire joints for permanence.

For those in the UK (and else where) 
the ducting is available
for RS components. The prices given 
are in UK pounds (multiply
by 1.5 for rough dollar prices)

Ducting Aluminium

 214-4714 Ducting,4in flexible,aluminium,3m     9.06
 257-9126 Ducting,flexible,aluminium,100mmx5m  14.42
 214-4720 Ducting,6in flexible,aluminium,3m    15.76
 257-9148 Ducting,flexible,aluminium,150mmx5m  23.69
 214-4742 Ducting,8in flexible,aluminium,3m    24.30
 257-9160 Ducting,flexible,aluminium,200mmx5m  36.05
 214-4758 Ducting,12in flexible,aluminium,5m   55.11

Ducting Fibreglass - would need covering

 193-5632 Ducting,flexible,4inx3m                8.70 
 257-9132 Ducting,flexible,fibreglass,100mmx10m 28.84
 193-5648 Ducting,flexible,6inx3m               12.88
 193-5654 Ducting,flexible,6inx6m               24.29
 257-9154 Ducting,flexible,fibreglass,150mmx10m 39.14
 193-5660 Ducting,flexible,8inx6m               36.14
 257-9176 Ducting,flexible,fibreglass,200mmx10m 56.65

Have fun,

Alan Sharp (UK)