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Domed Back Sunk In?


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I have been working on another acoustic and all has been going great. Except i made a big mistake and i kept the guitar body in my room over night after showing a friend.. and my room is so dry that my eyes usually burn if im in there too long. I then took it outside the next day which was a rainy 40 degree day with high humidity and my back plate seems to be a bowl instead of a dome now. Im not sure what to do at this point but i am very dissapointed. Any suggestions? This also caused the soundboard to split a very tiny bit (i made it worse trying to fix it).

Edit: What do you guys use as a humidifier when your guitar is in the case. I notice there are a bunch out there and they are all pretty cheap. Also... i like to keep my guitars on the wall because if they were in a case i probably wouldnt play it as much. If i keep my room at 45-50 humidity all the time (humidifier/dehumidifier) should i be ok doing that?

Edited by pariah223
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Sorry you are having problems.

Isn't there bracing on the inside to keep that from happening? The bracing should be curved to support the curve of the back. I'm surprised that it can move that much with the supports. It should crack the braces before it can move that much.

If you take it back into the "Dry" room, it will shrink, and you may be able to POP it back out a little at a time. A couple of wedges inside that you can gradually push together to spread the plates might work.

I suspect that this is going to give you a lot of headaches that may be resolved by starting over. You can take it apart and reuse some of the parts. If you are determined to save it, use the humidity problem as the solution.

Say you get it back to where you want it, how do you plan to keep this from happening again? You will coat the outside of the guitar with a finish, but the inside is still raw. It kinda sounds like your wood is not fully cured or kiln dry.

-John

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I did a little research and found out exactly what happened and found out how i should be able to fix it. I went to Taylor guitar's website and they had videos with EXACTLY the same problem i had. what happened, is when i brought it into my room that is like 0% humidity right now due to the dry heat in the winter, it dried out the wood and caused this to happen. If i would have kept it out in the humidity it would have been fine. If you click http://www.taylorguitars.com/contact/customerservice/ and go to videos there are a few humidity vids. I took a look at my other guitars i have, built and store bought and there having similer issues being in my room. I just fired up a humidifier and i gota grab a hygrometer and make sure i keep my room at the right humidity level. I wish i saw this video before i tried fixing the splits because beleive it or not, when he re-humidifies the guitar the splits close up!

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What radius did you use for your back?

Most people try to assemble in the winter or overdry a back slightly during assembly. Usually this will make the dome pop up a little stronger as the wood swells with an increase in moisture. You are safer that way, as assembling with a higher moisture level will create a situation where the wood will shrink and go concave or possibly even crack. If you do a little search on the web you should find a lot of discussion about this subject. I know some feel the month the guitar was assembled may be a clue as to why some guitars sound better or have survived a bit better. I recall reading about this on a forum, and several people had actually studied and measured the dome shape as it related to this.

You don't want to build too dry of course, but high humidity during assembly will lead to problems.

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I just had a conversation about humidity with the luthier who works on my cello. He keeps his shop at 50%. Winter's dryness is the most dangerous an instrument.

Yes, this is why you want to assemble in slightly dryer conditions. This way if moisture levels fall and the wood shrinks it hopefully does not go below the level at which it was assembled. If you assemble with higher moisture, and it dries significantly it is more stressful. This is also why many builders have taken to "baking" or overdrying soundboards prior to assembly, as this may help if the instrument is ever exposed to destructive low humidity levels.

Swelling or higher moisture levels generally are not that dangerous after an instrument is in service. So it is better to keep humidity up. Case humidifiers are a good safety measure. Winter tends to be a very dry season, especially when you are in a heated space with very cold outdoor temps(relative humidity drops when temp is raised vs outdoor ambient temp). The desert will destroy an acoustic instrument that was assembled in a moderate climate.

You need to keep the destinction between what is good during assembly, and what is good in service. How you assemble will set the level that is best for the in service conditions.

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