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MMD > Archives > April 2010 > 2010.04.14 > 12Prev  Next

Duo-Art Upright Suffers Bobbling Hammers
By John A. Tuttle

Hi All,  As James Black correctly notes in his original posting,
the pneumatic develops its greatest power at "time zero" [before it
closes].  And, as I recall, the Aeolian player action has rest rails
that the pneumatics rest on when they're at rest.  (Boy, does that
sound redundant!)  That being the case, it would seem reasonable that
lowering the rest rails in the bass region would change the power
curve such that there would be enough power to complete the sequence
of events in the piano action, i.e., move the jack out of the way, or
overcome the tension of the damper springs.

Naturally, this would also require readjusting the player-to-piano
action lost motion adjustment, but if there are enough threads to make
the change, it certainly wouldn't hurt anything.

James also asked about the tension of the bass damper springs.  They
are indeed stronger in the bass section, on purpose.  But, if they were
adjusted when the action was rebuilt, it seems entirely possible that
they were 'over' adjusted.  If so, there is most likely an obvious bend
in the spring at the point where the adjustment was made.

As a test, I would activate the damper pedal and try playing the music
softly with the player action.  If it performs flawlessly, that would
indicate that the damper springs could be the source of the problem.

In doing a little research before writing this posting, I came across
an excellent thread at in the Forum section.  The title
of the thread is 'Dampers and key weight': 

In it, Delwin D. Fandrich explains a common problem with bass dampers
in upright pianos.  He also describes a relatively simple fix that
involves adding split fishing weights to the damper wire, to
effectively increase the mass of the damper head, then decreasing
the spring tension so the damper still does its job.

What I find interesting and possibly very useful in James' situation is
the fact that by design, the spring increases in tension as the damper
lever gets pushed away from the strings.  By contrast, the added mass
of the weights remains constant.

So, if the problem is the damper springs, which would seem most likely
in this case, either decreasing the spring tension or moving the power
curve of the pneumatic to a higher point would solve the 'bubbling'
(which I believe is the correct terminology) problem.

In closing, there are other possible problems.  One that had me going
during one rebuild involved the damper spoon felt.  It was fairly worn,
and there was a 'wear groove' in the felts.  While the difference in the
friction wasn't noticeable when playing by hand, the player mechanism
'noticed' the difference.  After changing the felts, the problem was

Friction is the nemesis of a player action, so compare the notes that
work correctly with the notes that are having a problem.  See if you
can 'feel' any difference in the amount of effort it takes to get the
note to perform properly.

Another problem could be as simple as the leather nuts that hold the
striker wire to the pneumatic finger being too tight.  Those nuts
should never hold the wire to the finger 'snugly'.  There must be a
small amount of 'wiggle room'.  This is because the wire changes angle
as the bellows travels.  If it is reluctant to change angle, that will
introduce friction at the top, where the dowel passes through the guide.

Hope this helps solve the problem.

John A Tuttle
Brick, New Jersey, USA

P.S. Until reading this thread, I had never heard the term "bobbling"
hammers.  I have heard the terms 'bubbling', 'dancing', and 'bouncing'.
But, I must admit that it was the term 'bobbling' that caught my
interest.  When I think of bobbling, I think of those cute bobble heads
that people put on the dashboard of their cars.  ;-)

 [ Think of "When the Red, Red Roblin Comes Bob, Bob Bobblin' Along"  ;-)
 [ -- Robbie

(Message sent Wed 14 Apr 2010, 17:59:06 GMT, from time zone GMT-0400.)

Key Words in Subject:  Bobbling, Duo-Art, Hammers, Suffers, Upright

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