Hi Dennis,

I have repaired many cracks, including two long ones a few decades ago.
 
One was very bad, parts of one side of the crack being almost 1 cm lower
than the other.

The only things I had to remove were the strings near to the crack. I did
not need to disassemble anything else, and I worked from above the
soundboard obviously, and the owners were very pleased with the result.

At the time the only material available was Hubbard's 1963 booklet
"Harpsichord Regulating and Repairing", which describes soundboard repair by
shimming on p. 28. Essentially you do not reduce the crack, accept that the
soundboard has changed shape, and simply fill it.

These are the steps I use, derived from Hubbard's booklet:

- I find a suitable piece of a similar wood, but significantly thicker than
the soundboard. If the latter is 3mm thick, anything from 6 to 10mm will do.
This is the "shim".

- The shim should be as long as the crack, and width the same as the crack
enlarged (see below).

- First hard work. Both sides of the crack are usually vertical.
"Heroically" with chisel I enlarge the crack so that both sides have a slope
upwards, about 5 degrees each. Once this is done, the crack is visibly wider
on the top than on the bottom. This is needed in order to insert the shim
from above.

- Second hard work. With the chisel I give the shim a shape so that it will
fill the crack, going down at least as much as the soundboard depth. I try
repeatedly on the crack (no glue of course). If in places (or even the whole
of the shim) the part you do now see below the soundboard, goes a few
millimetres below the it, it will do no harm at all.

- Now I glue the shim in place (any glue will do).

- After the glue is completely dry, with chisel I shave the upper part of
the shim. I do this in two stages, the first leaving 1-2mm (to avoid cracks
in the shim), the second stage with a finer chisel, level with the
soundboard. I have managed to leave the shim perfectly level, but if you
find that there are a few depressions due to wood grain, this is of no
concern as soon as these are not an important part of the soundboard
thickness.

- If the crack goes below the bridge as in your case, I do two shimmings: up
to the bridge and after the bridge. This means that below the bridge the
crack remains open, with no shim. This will cause no acoustical effect at
all (unless the bridge has unglued from the soundboard in the region, in
which case you have to cut the bridge and shim it as well).

- If one side of the crack is higher than the other (common in long cracks
very near to the spine), you use weights to bring one side down. If this is
not enough, you use some tools to bring the other side up: these will need
some space in the crack, which you will fill with small shims later.

In my experience these repairs last forever.
 
My twopence worth ...

CDV




---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Note:  opinions  expressed on HPSCHD-L are those of the  individual con-
tributors and not necessarily  those of the list owners  nor of the Uni-
versity of Iowa.  For a brief  summary of list  commands, send mail to
[log in to unmask]  saying  HELP .
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::