Official Luthiers Forum!

last night i got my back braces arched and put on, however, instead of working on it in my workshop i decided to bring it into the house where it was warmer, when i woke up this morning and checked it the braces actually bowed the wrong way(brace side edges bowed out) and a crack formed in the upper bout about three inches down, should have stayed in the workshop .

I guess the humidity was much lower in the house, maybe more than 25% lower. Sorry...

_________________
Build log

Temperature means essentially nothing to wood in guitars other than how it effects humidity, which unless you are actively humidifying in the winter, warmer is worse.

If it cupped and cracked that quickly though, you should really check the humidity you're building at. If you're building in someplace like an unheated garage, you may be building under too humid conditions. If that's the case, you'll be better off to pull the braces from any top or back plates you have braced, re-acclimate them to a lower humidity, and start over with your bracing. Better to do it now than to have a completed guitar collapse after all the work is done.

_________________
Eschew obfuscation, espouse elucidation.

I have another back set i will just try it again new braces and all.

No need to replace the back. Just pull the braces, glue the crack, let it acclimate, and it should be fine. Done right, there should be no flaws whatsoever remaining.

_________________
Eschew obfuscation, espouse elucidation.

What was the % humidity in the house? Did you check it before doing any work there? When doing brace work or closeing the box, you should make sure the humidity is between 40% to 50% .And make sure the wood doesn't get any changes in temp or humidity for a couple of weeks prior and you will be alright. Good luck with your next try.

How long do you wait to acclimate braces and top? Say from 55 RH to 43 RH?

_________________
Here is what a Parlor Guitar is for!
http://www.youtube.com/watch?v=oEa8PkjO6_I

I've suffered the same but more in summer I know this doesn't help now but I only heat my workshop when I'm in it and store parts in the house if there's a large gap between times. Also I was given some slab sawn stuff which warped all over the place and had a crack I glued up before starting, and I've since come to realise that you really need correct wood, as I've been told that it's a splitty bit of wood anyway I can leave it in my bedroom the box was closed at 45% humidity and looking at the sensor my room is currently 37% and it seldom varies out of that sort of range, it was stored away from the sun, the radiators and drafty windows and I woke up one morning to find 2 splits in the back! In total now I've repaired 5 splits in the back, tried to fill some ripples in the back and they look worse for it! All a good learning curve and I have to of trodden the path myself as I would of guessed others for exaggerating unless I'd seen it with my own eyes/

_________________
Formerly JJH

I learn more from my mistakes than my successes