It can be shimmed (I recently had occasion for the first time to do so much shimming that I got pretty handy at the process), but you will want to apply some kind of pressure and backing from underneath to bring the two sides of the split to an even level. In my case, where there were openings with easy access in the bottom of the instrument, I made blocks of scrapwood thick enough not to flex, and with relief grooves where the crack/shim is/will be so the shim could go all the way in and be proud underneath, and then jacked the whole thing up from below with enough pressure to bring the two sides level with each other.
In a couple of cases I was able to do this with a set of tiny “go-bars” wedging the support block up from below, but in others I used one of those handly little screw jacks that piano folks use to support wrestplanks of pianos during the pounding of tuning pins into their holes during stringing. They’re not cheap, but work like a dream. Made by Starrett.
For the shimming, you will need to practice on something but the basic outline, as I learned it went like this:
1. Open up the crack so that it has a clean, uniform width, wide enough to take a shim of some substance, perhaps a bit more than 1mm wide. I used two expedients: a Japanese Azubiki saw, which is made to initiate cuts in floors or big carpentry mortises (q.v.) and the BACK of an XACTO blade burnished like a cabinet scraper. Google will show images of azebiki saws. Mine has a very thin kerf.
2. If you compress the shims, as described below, they will be flexible enough to follow any slight curvy waviness of the opened cracks, so those cracks do not need to be enlarged until they are dead straight.
3. Make your shims out of soundboard stock, and make their width slightly too great to enter the prepared open crack.
4. Compress the shims until they are so squished that they will slide all the way down into the crack and can be pulled back out again, going proud both top and bottom easily. A colleague simply rolls the shims with the round handle of an XACTO handle, but I came up with a really handy and better-controlled solution you’ll love: I ran the shims through my Italian-made Atlas Pasta Machine, which has thickness settings for the rollers, for different thicknesses of homemade pasta sheets, from “1” (about 2mm thick for ravioli) all the way up to “9”, which is very, very thin, presumably for Angel Hair pasta. I found that in general my shims (cypress for a cypress board) were just right for easy insertion when rolled at “7.” Works a dream, and the shims are flexible enough lengthwise to follow the wavy curve of a non-straight crack.
5. My colleague and I found that for this application, the best glue is, yes, I say (eating some crow) very fresh Franklin Liquid Hide glue. I put masking tape very close to the edges of the crack, applied the glue deep into the crack, very quickly inserted the shim to the desired depth (so a little sticks out up top and down underneath inside) and then wiped the excess glue clean with a wet cloth.
6. What happens, and you DO need to work quickly, even with the liquid glue, is that the shim, once it gets wet from glue and mopping-up, swells to its original size and locks itself into the crack with a great deal of strength. One shim I tried on scrap WITHOUT ANY GLUE AT ALL, proved, once it had dried, to be pretty much impossible to remove. Same principle as with modern so-called “biscuit joiners."
Although we all like to say that minor cracks in soundboards have little or no acoustical impact, in the case of the repairs I made (I found over 40 splits to shim in that soundboard) once things were “reconnected” the whole board generated a degree of acoustic response it had lacked previously.
At first it will be a source of anxiety, but once you get the hang of it, you’ll find the process rather enjoyable.
owen
On Dec 11, 2016, at 9:00 PM, HPSCHD-L automatic digest system <[log in to unmask]> wrote:
> There is 1 message totaling 27 lines in this issue.
>
>
> Dear members,
>
> I have a pianoforte which has water damage. One of the problems is the
> soundboard which has cracked in several places.
> The problem is the boards are now "wavy": 1 board is relatively straight,
> the adjoining plank makes an arc wel below the adjoining plank.
> I wonder if this can be repaired without further damaging the soundboard?
>
> Greetings,
>
> Chris.
Owen Daly Early Keyboard Instruments
557 Statesman St. NE
Salem, OR 97301
http://www.dalyharpsichords.com
(503)-362-9396
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