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Subject:
Soundboard repair - Directions for bad cracks - Some simplifications to Claudios advice
From:
Michael Bender <[log in to unmask]>
Reply To:
Harpsichords and Related Topics <[log in to unmask]>
Date:
Mon, 19 Dec 2016 14:15:47 +0000
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1st: Piano makers habe ready made shims, about 80 cm long. Just go there and buy some off.
2nd: I widen the crack with a V-shaped scraper I made from a usual rectangular scraper ("Ziehklinge") 

Warning: Soundboards are usually tanned after years. After  sanding or scraping the repaired area, the soundboard will be much lighter there. Do not try to stain this. Just wait three years and the shim will be almost invisible.
There is, of course, a different story about decorated soundboards.....

Cheers

Michael B


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-----Ursprüngliche Nachricht-----
Von: Harpsichords and Related Topics [mailto:[log in to unmask]] Im Auftrag von J. Claudio Di Veroli
Gesendet: Montag, 19. Dezember 2016 14:18
An: [log in to unmask]
Betreff: Soundboard repair - Directions for bad cracks

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




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[log in to unmask]  saying  HELP .
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