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Mr. Fusion
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A cage of my own
November 16, 2002 — 17:04

Yesterday
I had the brilliant idea of building the cage from folding the six great circles
of the icosidodecahedron.  I’ve always wanted to build these cages from
great circle folding, but for some reason I blanked out on the simple folding
shown in figure B on the right (click for larger version).

What I remembered was the disdyakis triacontahedron folding shown in figure
A, but I completely blanked out the folding for the polyhedra I’m using. 
Weird how your mind works like that.


So
Friday I bought some 22 gauge sheets of steel and started planning.  I
shook out the layout on some thick card paper first.  I got two of the six
circles required and thought it just might work.  This morning I laid out
one great circle (pattern shown on the left, click for larger image).  As
you can see, it’s just a ten sided polygon, with an 8" diameter circle cut out
of the center.


On
the right is three of the six great circles laid out on the sheet steel. 
You’ll have to click on the image for the full size.  It’s just scratching
on steel, so it’s pretty unexciting.  But it took a long time to lay out
all these circles accurately, so I thought I’d show it.

Naturally, the "right" way to do this is to have someone cut these out with a
laser cutter, or a plasma cutter.  The problem with cutting these out with
shears is the enormous amount of stress you put into the metal.  After I
had cut the edges and clipped the center circle out, the remaining piece was
pretty twisted.  Luckily, this is just mild steel and after I finished all
the bends, I ended up with a pretty nice fold (shown below and to the left).


From
this view, you really can’t see the curvature of the piece, but you can see that
the piece doesn’t look half bad.  When I saw the shape it was in before
folding and straightening, well…  It looked grim.

Anyway, using the great circle folding, I can now simply place the bar
magnets on the great circle’s edges.  They have oppositely opposed poles,
so everything just fits together wonderfully.  I have all the circles laid
out and I’ll cut them out tonight.  Of all the attempts so far, this is
certainly the easiest. 


To
the right is a better view of the folded great circle, showing the curvature of
the sphere that is formed by the folding.  The are only 24 welds necessary
to join the cage, and I think I can just wire the cage together by drilling some
small holes.  That would be cute.  I think I’ll still use the
conducting epoxy to glue the magnets onto the cage, though.  It has
excellent heat conduction properties.  I am kind of worried about having
the magnets hanging out in the path of the fusion products, but the cross
section isn’t huge.  Certainly it’s a lot better than my
first design which used ring magnets with
the cross section of a Barn (no, not the unit of nuclear cross section, the
Barn).

Getting this design into AutoCAD Inventor is proving to be non trivial. 
Can’t get things to line up so that the cage fits together.  Very
frustrating.  Must be missing something basic.  It’s trivial to put in
the flat patter, but I can’t use the sheet metal facilities of Inventor to save
my life so far.  Have to do some reading.


Well,
I cut out the outlines of the great circles (see picture at left).  Boy is
my arm tired.  Geesh.  I wish I knew someone with a X/Y laser or a
plasma cutting table.  But apart from a good workout for the old right
forearm, the result was surprisingly accurate.  The real stress to the
metal will come when I cut out the center circle.  However, I’m going to
try to cut radial lines before spiraling cuts to the circle like I did before.

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