There have been several postings lately using the word gusset and
I found myself confused by them until I figured out that some folks may
not know the true definition.  There were several old organ guys who
had the same confusion.  But I remember it from sewing patterns that
label the diamond shape of cloth found in the under arms of garments
as "gussets"

Let us get our terms correct.  In pipe organ and reed organ and player
piano bellows, a gusset refers to the diamond shaped piece of leather
that IS the corner of a reservoir.  The stiff pieces of wood or
cardboard, sometimes called ribs, serve several purposes, especially
keeping the sides of the bellows from popping in and out.  If a large
bellows is covered with bellows cloth and there is no stiffening
substance on the flat sides, you will notice that if it is used as
a feeder, the cloth will pop in and out with a loud pop or crack sound.
We add ribs to organ bellows to prevent this.

These ribs are attached to each other and the movable boards of the
bellows with stiff leather or bellows cloth.  I prefer leather myself,
but if it is an Aeolian Skinner organ, I use bellows cloth just like
the factory did for the rib strips.  I always use chrome tanned, very
flexible leather for the diamonds or gussets.

In player pianos, and some small organs, the bellows are all bellows
cloth with no gussets, but there is a stiffener applied to the sides
of the bellows cloth.  This is usually standard art supply chipboard,
but it should never be left out or you will have very noisy pedaling
going on in your player piano.

By the way, most leather gussets and rib hinge leather has chamfered
edges that cut away the bottom of the edge of the leather to a wedge
shape without cutting the shiny side of the leather.  This is lots more
work and is done with a razor blade or an extremely sharp felt knife.
Keep a whet stone handy.  Leather that is chamfered and glued down
makes for an edge that will not rub up and there is no edge of the
leather to seep air through the leather laterally.  Plus it looks
extremely neat and professional.

D.L. Bullock    St. Louis
www.thepianoworld.com