Dithering Hammers

[Alan Forsyth]

A message I tried to send a few weeks ago!


Hi guys,
I am Alan and have been servicing pianos in Edinburgh for the last 10 years
with also a previous short stint in Southern Africa.

I too have been baffled by the problem of dithering hammers in Yamaha
uprights (brand new) after re-regulating the set-off to 1/8". It seems to me
that the factory set the set off wider than usual to accommodate the muffler
rail so that the hammers would not block when the muffler rail was in the
down position. However, with the set-off being 1/4", without the muffler
rail (practise pedal) in use, does not give the piano a very dynamic touch
i.e. you cannot play very loud, and above all you cannot play very soft!
which is what "piano" is. The closer the set-off to the string the more
dynamic control the player has . Set- off is the point at which the jack
disengages from the butt and from then on the player has no control over the
hammer.

If the set-off is too far away you have less control from the moment of
escapement. Now in most actions if you regulate to 1/8" set-off and even
less in the treble, (I'm talking upright actions here) and all the other
measurements are left standard, the action works fine. But on some actions
this just does not happen as with Yamaha. Playing loud is fine, but as soon
as you play very softly, the hammer dithers.
Now this hammer dither is caused by the butt bouncing off the jack before
the hammer has had a chance to go in to check, and not by the balance hammer
bouncing off the check

 You mentioned a design problem, but just exactly where is the design
different from other actions? The only design feature I can think of is that
the length of the jack is too short. In other words there is not enough
leverage on the jack by the set-off button. If the jack were longer, the tip
of the jack would move much faster away from the butt during the aftertouch
motion. The jack must get out of the way faster than the hammer bounces off
the string! So to cure the problem is problematic; one can't obviously
lengthen the jack, but you might be able to increase the leverage on the
jack. I have tried moving the set-off rail closer to the jacks themselves
but this only seems to make a very slight difference. Changing the tension
of the butt springs does not solve the problem either. The only reasonable
solution I have found is to adjust the check distance much closer to the
strings. But then this becomes a non standard measurement, 1/4" instead of
1/2".

Of course all this begs the question; How softly is a piano supposed to
play? I have had many years experience playing piano in restaurants and
believe me, if there is a table right next to the piano, you have to play
VERY SOFTLY.

I sure hope one of you out there has not just a solution, but the correct
solution. This has been bugging me for years.

Best regards
Alan Forsyth