I have measured original factory Duo-Art accordions and made spacers
of the appropriate factory sizes. I have in the picture I sent [below],
two sets of these spacers so I can cover two at a time. The set on
the left are a set sold many years ago by Player Piano Company (PPCo,
Durrell Armstrong). This set is surprisingly correct to factory original
size.

The set on the right is the one I made decades ago and adjusted to
The factory specs when I discovered them by adding front rail paper
Punchings to correct their thickness. The thicknesses of the PPCo set
is notated on the spacers. The thicknesses are 0.2", 0.3", 0.4", and
0.65" measured in thousandths of an inch.

To use these I set the boards with these spacers in between and get out
my square to make sure everything is square. Then I use a short Harbor
Freight bar clamp and clamp the whole stack together. The side that
will have the glued seam is against the table. I clamp them together
and pivot the clamp so that it points out from the seam side.

Now I can apply glue to all 3 sides and cover them with the leather.
After drying awhile I remove the clamp and turn it over to dump out the
spacers so I can glue the remaining seam side.

I may be considered a charlatan because I no longer glue these with hot
glue, which I use for practically everything else. I glue them with
plastic glue: Aleene's Tacky Glue. The reason being that any hot glue
boogers that may be inside at the glue joints will harden and shred the
leather. With Tacky Glue, any glue boogers inside are flexible and will
take many years to damage the leather.

Yes, it must be covered in pouch leather -- preferably tan, because the
white is very much more leaky than the tan leather.

After the glue dries, and before I cut any holes for screws or tubing,
I separate one egg and whisk the egg white and pour it into a flat
brownie pan. Each accordion segment gets set down in the egg on all four
sides and set up to dry. Then it gets one more dredging through the egg
white when dry.

Egg white has been used for hundreds of years as a bonding agent in
leather tanning and craft work. It is historically accurate as factories
always used this method.

I hope this helps to avoid the problems I see from previous restorers of
Duo-Art systems so that we can get back the correct factory methods which
only worked well for 111 years!

Doug L. Bullock - Piano World Enterprises
Alton, Illinois
https://www.thepianoworld.com/ 
https://www.facebook.com/PianoWorldEnterprises 

[ Duo-Art accordion spacers
[ https://www.mmdigest.com/Attachments/23/09/09/230909_224347_DA_accordion_spacers.jpg