I, too, just recently rebuilt the expression box on my Duo-Art, on a
1925 Weber piano.  As I am writing this on the road, I can't look up
all of the reference material, so I don't remember exactly where I
found all my information.

I don't remember where I saw the suggested spring rates, but I was
looking for .049" wire for accompaniment, and .051" for theme.  They
are 1/2" springs, I believe.  I could not find 1/2" springs of .051"
inch wire, so I simply bought a long (8 inch) .049" spring, and cut it
in half.  I used half for accompaniment and half for theme.  Therefore,
both accompaniment and theme regulator springs are exactly the same
spring rate.  It sure works a lot better than the unmatched springs
that were on the unit.

You wouldn't believe that the accordion pneumatics had 3 (yep, that's
right, three) levels of covering.  There was the original rotten pouch
leather, and two additional coverings of pneumatic cloth.  It's amazing
it ever worked at all, but it did.  I used kangaroo pouch leather for
the recovering.  Would you believe the accordion pneumatics now work
faster than before?  And I set up the accordions using a dial
indicator, so the displacement is exactly as it is supposed to be.

This AMICA article had a novel approach for breaking apart the
expression box.  The procedure was to put a hardwood driver through
the box and break it apart with a hard impact, with the box sitting on
a soft rug on the floor.

I was scared to death, as Kitner suggested using a knife to break it
apart.  But I did exactly as recommended, and I hit it HARD.  The
result was, as suggested by the author of this article, a magical,
almost religious experience.  The box broke apart right on the seam,
absolutely perfectly.  Not one split or sliver anywhere.  If anyone
wants to know about this article, I'd be happy to look it up for you
when I get home.

Ray Fairfield