THUD

[Jon Page]

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Roger,
The Damper upstop rail slapping on the belly rail is a good candidate.

Hardened guide rail felt is another possibility along with the damper head
itself being a bit loose on the wire.

Hmmmmmm...

Jon Page

At 11:50 PM 12/02/2000 -0600, you wrote:
>Hi John,
>           Guess we could be grasping at straws, but a couple of other
>things to try.
>
>Is the damper guide rail secure to the belly rail?
>
>If the board is flat in this area, that can cause some thud like tones.
>Measure the bearing with a compound gauge, and check the board for some
>curvature.
>
>If the glue joint on the inner rim or belly rail is loose similar
>result.
>Take an artist pallet knife, (.010" thick) and see if you can find any
>looseness between the board and liner.
>
>Just some thought's
>Roger
>
>
>John D. Chapman wrote:
> >
> > Remember THUD?
> > Here is the history.  I had not seen this piano until last month.
> > While tuning I noticed that notes 50, 51, 52, and 53 (top four notes in
> > agraff section,  just below the treble break) had an unpleasant
> > knock/slap sound, the same percussive knock which is in the background of
> > all piano tone, but in notes 50-53 it dominates the tone.  These are the
> > four notes between A440 and the treble break.  The orchestra conductor
> > asked me if I had noticed those four notes, as did the pianist, so I knew
> > it wasn't just my imagination. I have checked it out both upstage and back
> > stage (wood floors), and back at the dealership (concrete floor).
> >         Here is what we have done so far:
> > 1.  checked hammers for loose glue joint, flange pinning, and screw
> > tightness,
> > 2.  visually checked the action frame joints between notes #53 & #54,
> > 3.  checked the wippens for sufficient felt at the front to keep the
> > jack from slamming into the rep lever,
> > 4.  checked key frame bedding, front, back, and glides, with and without
> > damper pedal, and with and without shift pedal,
> > 5.  pressed down the back key frame with a long screwdriver to see if it
> > was slapping up against the dag,
> > 6.  played notes with dampers held all the way up by hand and by pedal,
> > 7.  moved the action in and out to see if the tone improved,
> > 8.  switched some hammers from the octave below to see if it could be the
> > hammers,
> > 9.  switched some whippins from the octave below to see if it coulb be the
> > whippins,
> > 10.  seated the strings,
> > 11.  applied firm pressure on the bridge cap at the end of the section to
> > see if there was a loose glue joint between cap and bridge body,
> > 12.  checked for clearance between the bridge and the plate,
> > 13.  checked for loose ribs,
> > 14.  checked for clearance between nose and bell bolts and soundboard,
> > 15.  checked that the bell bolt nut which was one turn past finger tight,
> > 16.  checked for foreign object lodged between soundboard and frame, and
> > between soundboard and plate,
> > 17.  tightened the end screws of the diagonal plate bar, which could be
> > turned another half turn to snug,
> > 18.  checked key leads and underlever leads,
> > 19.  checked the key bed with a straightedge front to back.  I found that
> > the board just beyond the board on which the balance rail glides rest was
> > high.  Chalked it where it passes under the front to back board of the key
> > frame which is just under notes 50-53 and found that is was just barely
> > touching. Sanded key frame there until there was adequate clearance.
> > Playing the note by pushing up on the whippin from underneath with my
> > finger without moving the key still produces the THUD, so I guess that
> > eliminates the keyframe anyway.
> >
> > None of this has changed the THUD.
> > What have I missed?
> > Why these four consecutive notes  with no sign of the problem above or
> > below them?
> >
> > John Chapman RPT
> > Wake Forest University
> > Winston-Salem NC

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