Hello MMD.  After several months of progress at glacial speed,
I'm finally reassembling the expression box from my Half Duo-Art.
I successfully broke the box open using the John Grant freezing and
hammer technique, but, not being sure that I could pronounce the
"Hi-Eee-Aah-Yah" cry properly (I can't even spell it), I yelled out
"Geronimo" instead.  This does seem to work just as effectively.

The originally glued-together box is now a screwed-together box.
I glued a leather gasket to the bottom of the top half of the box,
and then clamped the two halves of the box together again.  Using
a standard length 5/32-inch drill I bored eight holes down through the
walls of the box, choosing sites where the new holes wouldn't interfere
with any existing holes.  This gave me three holes along each long side
of the box, and one hole in the middle at each end.  I then switched
over to a "long series" 5/32-inch drill, which was almost 5-1/2 inches
long and extended my holes down into the bottom half of the box.

I used the shorter drill first on the advice of the lab manager at
the University of Tasmania's Physics Dept., where I was semi-legally
doing all this.  (I don't feel bad about this at all; they've got me
back in there running a weekly lab class this semester, after nearly
eight years of retirement.  They must really be short-staffed.)

I enlarged the holes in the bottom half of the box to 1/4-inch diameter
and epoxied into them pieces of 1/4-inch brass rod about 3/4-inch long,
drilled and tapped with a 5/32-inch thread.  The longest 5/32-inch
machine screws I could get were three inches long, not quite long
enough, so I counterbored the holes in the top half of the box to
a depth of about 1/2 inch, using a drill bit with a diameter slightly
larger than that of the screw heads.  This suited me well; it got the
screw heads out of the way.

To ensure airtightness at the new gasket, I glued a 3/4-inch-wide
ribbon of pneumatic cloth right around the outside of the box, where
the two halves joined.

Inside the bottom half of the box, and inspired by a posting of a year
or two ago by Spencer Chase, I replaced the inner bushing cloth bearing
for the control shaft with one made out of a plastic called Delrin.
This was made by a friend who also made a Delrin bearing for the other
hole where the control shaft emerges from the box.  Unfortunately the
bearings were made to a higher precision than was the box, and, since
the original holes weren't perfectly aligned, the shaft was binding on
the inner bearing.  So I changed the outer bearing back to bushing
cloth and the problem went away.  In the future, if necessary, the
inner Delrin bearing can be changed back to bushing cloth too; I did
not remove any extra wood.

When I re-assembled the knife valve, I kept the spring pressure on the
moving surface fairly low.  It doesn't show any signs of wanting to
part from the fixed surface, and in service there will be some extra
force on it due to the pressure difference between controlled and
uncontrolled vacuum.  At present, the shaft rotates much more smoothly
than it did before I pulled things apart.

John Phillips in Hobart, Tasmania