[pianotech] Regulation mystery

[David Nereson]

    I've regulated lost motion on a Yamaha U1 in the winter one 
year, only to have to re-regulate it in the summer because (I 
assume) the keybed had swelled in thickness, thus lifting the 
keys and holding the hammers off the rail.  I don't know how 
else to explain it.
    --David Nereson, RPT, Denver, CO

----- Original Message ----- 
From: "David Lawson" <dlawson at davidlawsonspianos.com.au>
To: <pianotech at ptg.org>
Sent: Sunday, October 24, 2010 2:02 AM
Subject: [pianotech] Regulation mystery


I regularly service about twenty pianos at a Conservatorium, 
both uprights and grands. The uprights are mostly Yamaha U1 
models about 15 to twenty years old, with a couple of Kawai KS 
models also. I regulate the lost motion on these instruments so 
that the capstan holds the wippen so there is no lost motion, 
however, it is not holding the hammer off the rest. I have just 
finished the regular maintenance of these this week, and 
discovered that all but one had increased the height of the 
capstans to hold the hammers off the hammerest by about 1/4 inch 
or 6cm. My first reaction was that someone had been at them, 
turning up the capstan. However, this is not possible as I am 
the only tech. who attends to these pianos.
So, my question is this: Would the sudden change from 
drought,(about ten years) to very wet conditions, have brought 
on this amazing change? I find it difficult to believe that this 
much change could be brought about by humidity. Let's face it, 
the metal pin holding the capstan is tight into the rear of the 
key, which would surely not increase the height by this much 
with humidity! I checked the back touch on the key-frame, and it 
seems quite normal.The only piano that did not have this happen 
to it, had an additional heater in that room, which may give us 
a clue.
Your thoughts please.
David Lawson Wangaratta Australia