Dear MMDers,  I am currently restoring the Duo-Art mechanism in a
very late Steinway reproducing piano, serial number 279076, indicating
manufacture sometime in 1935.  This instrument incorporates the
fan-accordion expression system and the Aeolian-modified Ampico B
drawer, as well as a non-extended case.

Having just gotten to the stack (two decks of forty 'narrow' pneumatics),
I was very surprised to see that Aeolian positioned two guide pins (cut
off center pins) between each striker and its deck.  The purpose
appears to have been alignment of the striker pneumatics on the deck.

These short pins are not visible from the outside (hidden) unless the
pneumatics are removed from the deck.  One has to exercise great care
in removing these delicate pneumatics, because twisting the fixed
boards can cause significant damage to the strikers or the decks, or
both.

The aforementioned guide pins will substantially aid in the precise
repositioning and re-gluing of the strikers on the decks after they have
been recovered with high quality pneumatic cloth.  In hindsight, the
use of guide pins seems obvious, but I have never encountered them
before in the restoration of any pneumatically-operated self-playing
piano.  Nevertheless, Aeolian must have felt justified in expending the
extra effort or they would not have done so (material cost was likely
negligible), especially in 1935.

Have any other MMDers ever run across the use of hidden guide pins
in the placement of striker pneumatics on the decks of any player or
reproducing pianos?  What was Aeolian (Aeolian-American?) thinking in
1935?  Do you have any other thoughts that might shed light on this
unusual and/or clever stack implementation?

Thank you for your thoughts,
Bill Koenigsberg
Concord, Massachusetts