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MMD > Archives > April 2010 > 2010.04.14 > 11Prev  Next

Duo-Art Upright Suffers Bobbling Hammers
By Randolph Herr

[ James Black wrote to Randolph:

> I have thought of putting in hinge springs on the pneumatics of
> varying strength to compensate, i.e., stronger springs at the treble
> end to compensate for a lighter action.  My Duo-Art at present has
> none although I do know that some early versions did have them.
> What do you think?

Hi James,  Aeolian used phosphor bronze wire to make torsion springs
at the hinge of certain pneumatics.  A few technicians have commented
on peculiar small scratch marks found on unrestored action stacks,
and it appears that when Aeolian was regulating the player, if a note
was weaker than its neighbors, they would stick in a tool that would
fit under the spring and push it out of the wood.  The result was
a stronger note.

It also appears that Aeolian put the wire spring on certain groups
of notes, I believe always in the treble.  This was to compensate for
the treble not only having a lighter hammer but there was no damper
to lift up either.

I have found a method to regulate grand stacks that involve using
leather nuts so that the pneumatics are a little more closed than
normal, and are no longer resting on the felt cushion.  When a weak
note is encountered, you can open the pneumatic a little wider to
make it a little stronger.

Another simpler way is to cut away some of the felt cushion under the
pneumatic.  This could be done on upright stacks as well.  Of course,
you could lightly glue a piece of bushing cloth to the bottom of each
pneumatic, and when you encounter a weak note, the bushing cloth can be
removed and the pneumatic made stronger.

Two things are important to know:  First, after any kind of regulation,
the system must be checked for lost motion or the opposite.  The second
thing is that these are pretty fine and subtle changes, and having a
hinge-bound pneumatic, or any other similar condition, will be too
coarse for the fine adjustment.  I can sell you the right phosphor
bronze wire if you can't get it easily.

Putting the torsion springs into pneumatics that are already glued to
the deck is delicate and high precision work.  I wonder if putting in
weaker damper springs, or weakening the existing springs might not
solve your problem as well.

Do you know anything about measuring the down-weight and up-weight of
a key in an action?  I can offer some help if you want.

Randolph Herr

(Message sent Wed 14 Apr 2010, 03:45:23 GMT, from time zone GMT-0400.)

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

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