Re: Source for Aluminum Spheres (up to 12" threaded)

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Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 08:53 AM 10/24/2003 -0600, you wrote:
>Original poster: "RIAA/MPAA's Worst Nightmare" <mike.marcum-at-zoomtown-dot-com>
>Thanks for the link. 22" is a decent size for most TC's, but what if I
>wanted to build a giant vdg? Any cheap source for 36"+? I read somewhere
>someone tried to cut the ends off a big propane tank, weld them together,
>and use that until he realized it was much too heavy (lol).

You're only hope for large spheres is to either find someone making 
spherical tanks (which will be quite heavy) or to call up metal spinning 
companies and hope one has the form in the size you need.

Around here, they make spherical propane tanks, and also spherical mooring 
floats for ships (not boats, but we're talking ships that carry thousands 
of tons). Steel, heavy, etc.

The other alternative, discussed at length in the archives over the years, 
is doing some sort of substructure/armature and coating it with a 
conductive coating (be it tape, foil, evaporated metal, etc.)



They're not going to be cheap, no matter how you look at it.  Hundreds of 
dollars would not be surprising for a 1 meter sphere.

If you've got a lot of time, you could probably make a curved form/die with 
the right radius of curvature, and beat a lot of smaller segments of 
aluminum into the right shape, then do very good seam welds/brazes, 
grinding it smooth.  Essentially aluminum sheet metal  body work.  You'd be 
surprised how good a job someone who is skilled at this can do.  You'll 
need a set of body working tools, and a set of slip rolls to do the beading 
on the edge to make brazing/welding feasible.

If you've got some BIG capacitors around, or access to explosives, and a 
swimming pool, you could contemplate hydroforming the segments.

The aluminum sheet for this approach can be quite thin, because the seams, 
if done right, make it very strong.  Thin aluminum is easier to form to the 
curves necessary.  One can build a large sphere out of triangular (curved) 
tiles. Depending on the geometry, you may only need 2 or 3 kinds of 
triangles, meaning it can be a sort of "mass production" operation.  For 
large sizes, epoxy would make a fine way to join them.  Just roll a flange, 
glue flanges together, then use conductive epoxy in the joins on the 
outside to make a smooth surface.