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:
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