Hi Dean, this is just my take on it, based on wood movement and RH, obviously not from some vast repository of experience...
I'd say, if the wood was acclimated and the RH was in the "happy range" during the process of gluing on the back braces, through the time of gluing the back on, then I'd guess that this may be repairable. You may get away with swelling the crack shut by putting the box in humidity, then wick-in some CA, and let the box come back down to the shop RH. I suspect your shop RH (in Wisconsin) is about like mine (in Minnesota), and that right now, the RH is staying around 40% to 60%. Spring: the time after humidifiers and before dehumidifiers. And, if I'm reading your notes correctly, you buttoned this up in fall. Fall: the time after dehumidifiers and before humidifiers. With a dry spell between. Actually, I'm kind of surprised that the crack is still open, now that there is "normal" humidity. Has the crack closed up some, on its own, between the driest part of winter and now? If the box was closed up in about the same humidity as now, then since the crack hasn't closed up on its own, it makes me wonder if the abrupt force of wood movement in the drying process overcame the forces of the glue on the back bracing (somewhat) causing some creep, and that now the gentle forces of the wood swelling are not quite enough to let the back move as it would if unbraced. In other words, if the glue on the braces is now resisting allowing the back to swell and close the crack. If the box was closed in about the same RH as now, I think I'd take a shot at forcing the crack to close, by humidifying the box, and then glue it shut. It's worth a shot.
Not specific to this Bocote back, just thinking out loud:
When I would think it is a lost cause is when the wood was at a high RH (swollen, wider than 'normal') at the time when bracing the back and attaching the back to the rims, and the back was then trimmed to fit the box. I say 'lost cause' because even if you add moisture and close the cracks and glue, it will fail again under normal to dry RH. Even if someone would carefully take the back off and remove the braces, fix the cracks and re-brace, the back at a normal RH would be slightly too narrow for the box. I suppose if you had not yet cut out for binding, or if you were willing to add purfling, or add tiny wings to the tips of the lower bouts, then you could always salvage it, so maybe 'lost cause' is a bit overboard - but it would be challenging when it got to the correct RH and it was a bit too narrow for the box.
So there, you asked for thoughts, and I'm always thinking too much
so I gave you a bunch of mine.Keep us in the loop on this - it will be interesting to see how you handle it and how it goes.
Dennis
). I'll make it look good.
