THUD

[Horace Greeley]

Hi, John,

Rereading this stuff, I really do not think that this is a hammer problem 
(and would probably leave them alone) I keep coming back to your #19 -

> > > 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.

I am not sure that what you describe does eliminate the keyframe.

The forefinishing process is very different than it used to be.  There is 
much less attempt to create the opposing compound, complex curves than 
there used to be.  It is possible that there are other areas of the 
keyframe which are touching and transmitting this sound through the 
keyframe/keybed structure.

The keybed should not be dead level at any point save across the width of 
the area in which it supports the back rail.  At all other points, it 
should describe an arc of varying radii as you move your straight-edge from 
the bass through the treble.  The arc should have a larger radius at the 
ends of the keybed, and a shorter one in the middle (compensating for the 
slight rise in the middle of the area supporting the front rail of the 
keyframe..well, ok, the one that used to be part of the construction, 
anyway).  The keyframe should be similarly concave, so that the arcs of 
each are opposed, not together.  The whole is pulled together under tension 
created at the front rail by the cheek blocks, at the center rail by the 
glides, and, at the back rail by the mass of the action and (contrary to 
what seems to be popular opinion) the dags.  (Very) nominally, the center 
of the keybed, along a line roughly through the glide supports, will be 2mm 
lower than the front and back rails.  The back rail will be dead 
level.  The front rail will, perhaps, have the traditional 2mm rise in the 
middle which is distributed evenly out to the ends.  That was the bad old 
days.  Now days, there is often simply what amounts to a coarse hacking at 
the last several inches of the keybed as it approaches the cheek 
blocks.  If that is the case, it will need to be smoothed out before any 
real bedding of the keyframe can take place.

I would start with working on the keybed.  The reason for this is that the 
newer keyframes are flexible enough already, and to not need to be made any 
more so (than is absolutely necessary).  Avoid the temptation to work on 
the keyframe first, and deal with its foundation, the keybed.

OK, I admit, this is really a long shot; but that seems to me to be the 
point you have reached.

This one is a real hairball.  My orange longhair cat would be proud.

Best.

Horace