Bobbling hammers of Yamaha Uprights

[Isaac OLEG]

James,

Thanks for those comments, what you have find seem to go in the
direction of my finding as well (or I did not understood well)

Did you dismount the butts to compare them ?. What caused it to start
to do it now and not before ?.

I've been suspecting an extra compression of the butt cushion that
produce that shape change at the butt leather because of wear.

That happen as well on older pianos repaired if the cushion employed
is too thin.
Indeed the jack have less space then to get out of the way, but is not
also the hammer leverage (impulse) of the bad parts different from
neighbors ?

Said that because new parts are generally very even, a shape
difference at the butt may not be that large, so the reason may hide
elsewhere.

If we work on a 10 -15 years old vertical, the wear at the butt
leather allow us to regulate the jack too high in his rest position.
Then the stroke geometry is disturbed from the start.
I noticed that when giving some air at the capstan then, we sometime
find a place that seem to be the original position of the jack when
the action was not worn as much.

Then the propulsion of the hammer get more natural, stay powerful
despite the apparent play. I believe the jack then have find back its
original geometry when he push the butt (there is a definite feel for
it in the key, and even if the beginning of the touch may look fuzzy,
no real play is noticed).
More than that, if I think about it, if a minimal play between Jack
and butt on those (slightly) worn action is used, there is possibly a
lot of friction at the beginning of the stroke, as the jack tend to
crunch in the cushion, as the force of the hammer apply more on the
back part of the jack (particularly if the hammer stroke is not
corrected and is larger than originally).

So things get worse soon after you have conscientiously regulated the
minimal play.

New cushions indeed may seem the appropriate answer asap. There is
another point I don't miss now, the key height may be kept consistent
BEFORE any attempt to regulate the play (just normal regulation
sequence indeed !)

Getting back the key height where it belongs is often the most
efficient improvement in a quick job (and solve the jack play partly
as well).


Best Regards

Isaac OLEG




-----Message d'origine-----
De : caut-bounces@ptg.org [mailto:caut-bounces@ptg.org]De la part de
James Ellis
Envoye : dimanche 18 avril 2004 22:45
A : caut@ptg.org
Objet : Bobbling hammers of Yamaha Uprights


I have been reading your various posts on the subject of bobbling
hammers
on Yamaha uprights.  I tune a fairly new Yamaha P22 that has just
started
doing it on a few hammers, but by no means all of them.  I looked
closely
to see why.  It is NOT regulation.  It is NOT damper spring strength.
It
is NOT that I don't follow through on the key stroke.  In fact, most
of the
hammers don't bobble, no matter how I play.  On those that do, I have
to
pound hard, or they will.  Those things I just mentioned: NONE OF THE
ABOVE.

Here is what I found.  It's the shape of the butt and butt leather.
On
those that are bobbling, there is more of a lump at the very front of
the
leather than on those that don't bobble.  I found two hammers, side by
side.  One always bobbled, unless I banged it hard.  The other never
did.
I pressed both keys down firmly.  Both jacks moved back by the same
distance. One bumped the outward end of the butt leather, but the
other did
not.  This is the only piano I tune regularly that has this problem,
but it
does, and on a few notes, it has it bad.  Otherwise, it's a very nice
piano.

Keep this in mind before you go bending things as a quick fix.  The
quick
fix is a tiny bit more dip, or a tiny bit closer checking, or a very
slightly sooner let off, or a combination of all.  But that's not the
real
fix.  The real fix would be to get that hump off the front end of the
butt
learher.  Otherwise, the jack will have to fly way back, farther than
it
should, to clear it.

That's what I found on this particular piano.

Jim Ellis


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