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So essentially I was making a bowed lyre (jouhikko/tagelharpa), which requires a thin spruce soundboard. I am going to make it by gluing three boards together as shown in this YouTube video:

https://youtu.be//watch?v=dfjMi0_kjw8

Instead of just hollowing out a chamber through all three planks and slapping a thin board on top and bottom, I decided to thin the top board down to the required 4mm to make the playable soundboard that would connect with the rest of the frame. However, due to a number or factors (plank was warped, I foolishly chiseled along the grain), the board became too thin in a number of places and even cracked through in one corner. So the question is: is it still salvageable? I was thinking of eliminating the broken corner by drilling a sound hole through it, which would also stop the crack from spreading, same with other thinned places. Another option would also be to apply a sawdust and PVA paste to the thinned places to fill them in and make them stronger (the soundboard has to support 20kg of string tension). However, I'm not sure any option is optimal at all. It might hold at first even without reinforcement, but sooner or later one of the chipped places will start a crack. Maybe adding as many thin cleats as possible could prevent this splitting? I understand that the question would be more suitable for luthiers, but the situation here is simply finding a way to consolidate a spruce board that is too thin by filling in the flaked-out gaps or any other suitable approach. The treatment and its ugliness do not matter, since the repair will be on the inside- only the integrity of the soundboard. Thank you!

Only 2 photos allowed on the post, so the rest are in

https://photobucket.com/albums/s437/Antanas_Melinis/18834514_1362603947162377_878710737_n_zpsq2bib1bp.jpg

https://photobucket.com/albums/s437/Antanas_Melinis/18871245_1362603960495709_1269244673_n_zps5alofw26.jpg

https://photobucket.com/albums/s437/Antanas_Melinis/18815917_1362604037162368_1834044473_n_zpsuq8jj2qc.jpg

https://photobucket.com/albums/s437/Antanas_Melinis/18816828_1362604067162365_361181297_n_zpsg6rbmmsj.jpg

 **General view of the hollowed-out plank**  **light shines through the thinnest parts**

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For best results, starting over would be the way to go; no question. Adding fillers and the like will change the tonal qualities for the worse.

However this your project, you can soldier on if you wish. Many instruments have been made with less than perfect material. And many instruments are quite workable with splits. Check out tone tapping wood (this will give you feedback regard changes to tonal quality of the wood) and take look at how other makers secure thin sound boards. Harp makers and guitar makers deal with splits all the time (glue and clamping mostly) also check how folk reinforce sound boards on different instruments. (I've even seen grommets or small patches of wood attached to add strength.)

Since part of the project is for you to learn, if you decide, this can be an experiment where you learn where is possible and what it is not. Good luck.

  • 1
    Agreed. No telling how it will sound/work/last until you try, and it'll be good practice even if you have to scrap it. – FreeMan Jun 13 '17 at 15:12
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Sawdust & PVA will not have the same resonance as the wood. It will probably sound dull. In my opinion this is not salvageable if you want something that sounds decent.

  • Would you think that even a small amount of filler (in the chips and a along the edges) would dampen the sound too much? Maybe it would be offset by the fact that the board itself is not glued to the frame, but actually transmits the vibrations directly through? It's my first time building anything more complex than a flute, so thank you! – A.Melinis Jun 9 '17 at 22:50

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