Bass hammer checking

[Dave Nereson]

----- Original Message -----
From: Phillip L Ford <fordpiano@lycos.com>
To: <pianotech@ptg.org>
Sent: Thursday, March 14, 2002 6:45 PM
Subject: Bass hammer checking


> Yesterday I worked on an older Baldwin with a Schwander action that
> had a characteristic that I've encountered on other grand pianos,
> some having it more than others.  The hammers check perfectly on the
> bench or when the action is pulled out in your lap, but won't check when
> the action is in the piano.  This behavior is usually only noticeable in
the
> low end of the scale and becomes most pronounced at the bottom.  On some
> pianos it seems that you can't get the hammers at the bottom end to truly
> check no matter what you do; make the checking shallower, make it deeper,
> groove the tail, rough up the check leather, change the back check angle,
> reduce rep spring strength to almost nothing, etc.  When I say 'truly
check'
> I mean behave as in the rest of the piano.  The hammer is held
> some distance below the string when the key is down and rises
> when the key is released.  Apparently some sort of 'checking'
> is going on because even on a hard blow the hammers don't bounce back to
> the strings.  But the tail isn't really being held by the backcheck when
the
> key is down.  What's the reason for this?
 > Phillip Ford

        Yup, I've encountered this also.  I find that when you pull an
action out onto your lap, supporting it mainly by the front rail, with the
back rail still resting on the keybed, the hammers won't check.  Sometimes
let-off and drop won't happen at the same place either.  I'm sure it's
because the whole keyframe is now flexing such that the balance rail is
lower than when it's sitting on glide bolts in the action cavity.  So I lift
up with my toes, pushing the balance rail up with my knees.  This is
uncomfortable of course, but if it's just to adjust a few backchecks, that's
OK.
    However,  there are still times, as you say, when no matter what you do,
the hammers in the low bass won't check, especially on a soft blow.   As
someone else said, sometimes the hammer tails are too smooth (slightly
"glazed") and taking a few crosswise swipes with a sandpaper paddle will
make them check again, but for how long?
    I have a grand action model on which no one has been able to get the
hammer to check on a soft blow.  You can get it to check if you really do a
karate chop on the key, but otherwise no.  As others have said, the problem
must be in the length and arc of the hammer tail and (possibly) the shape of
the backcheck.  All manner of different backcheck angles have already been
tried and nothing works.
    I would say live with it unless the player demands perfection in the
regulation, or take the hammers off and re-arc the tails, possibly grafting
on wood if necessary for a wider radius or longer length.  --David Nereson,
RPT, Denver