Hi,  Could someone with a knowledge of pianola mechanisms re-visit my
inquiry dated late last month [17.10.30 MMDigest --
https://www.mmdigest.com/Archives/Digests/201710/2017.10.30.03.html ]
and advise me on how a pianola roll can be made to track properly by
the mechanism sensing the edge of the roll using air pulled through the
outside hole on the right hand side of the tracker bar.

This hole has a small vertical slot about 3/16 of a inch long and 1/16
inch deep and seems to connect to a bellows inside the unit through
rubber tubes.  The mechanism then moves the roll back and forth to keep
the edge of the roll tracking properly.

The principle of the operation escapes me.  I think there may be a part
or valve missing.  If there is anyone with one of these roll playing
units could they please send me a photo and a explanation of how such
a unit might control the paper roll position.  This would be very much
appreciated.

Michael Taylor

 [ When the hole or slot is covered the tracking system should not move.
 [ Otherwise, air flowing through the sensing slot is the signal that
 [ activates a valve that applies vacuum to the tracking pneumatic.
 [ The tiny aperture which supplies vacuum to the sensing hole is easily
 [ clogged by paper dust.  -- Robbie