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pronounced bump in the center of a guitars back
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10137&t=51651
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Author:  Conor_Searl [ Tue Feb 26, 2019 12:28 pm ]
Post subject:  pronounced bump in the center of a guitars back

This is a guitar I've been dealing with in my re-humidification thread, but this is another issue (possibly related). The guitar is an Alavarez dreadnought, and right in the center of the back there is a pronounced bump and you can slightly feel the edges of the back stripe through the finish. But only in the center of the back, as you trace your fingers along the back stripe towards the neck or end pin it goes smooth again. Initially I thought it must be due to the guitar drying out, but the back graft inside is solid, I can't get any feeler guages under it, same with all the bracing around it. On the outside, while I can feel the back stripe, the finish is sound, there are no obvious cracks, and pushing on the bump does nothing. Is this possibly just a mistake that was built into the guitar, or is it a symptom of something else I'm missing?

Author:  Barry Daniels [ Tue Feb 26, 2019 12:41 pm ]
Post subject:  Re: pronounced bump in the center of a guitars back

Photos?

Author:  Conor_Searl [ Tue Feb 26, 2019 1:18 pm ]
Post subject:  Re: pronounced bump in the center of a guitars back

Honestly there's not much to be seen. I tried to catch it with my phone camera but to no avail.

Its about 6" along the herringbone in the center of the back (the space between the tape,) but the middle inch and a half is the worst. And as I look at it more, it feels almost like the treble back side is sitting proud of the bass side in the center of the back. Like I mentioned earlier everything seems solid, no obvious loose anything inside. When you push on the bump nothing really happens. The back flexes a bit but not more than any other guitar. This is a pretty nice guitar, solid rosewood back from what I can tell.

Author:  Barry Daniels [ Tue Feb 26, 2019 1:41 pm ]
Post subject:  Re: pronounced bump in the center of a guitars back

If nothing is loose and there are no bad side effects, then I would consider it a non-problem. Just have the owner keep an eye on it and if it doesn't get worse in the future then call it a feature ;-)

Sometimes these plywood plates move and bulge more than solid wood but if nothing is loose then there really is nothing you could do about it other than add a beefier brace, but that could have unintended sonic effects.

Author:  WudWerkr [ Thu Mar 14, 2019 10:46 am ]
Post subject:  Re: pronounced bump in the center of a guitars back

I wonder if the back "tater chip'd" a little when it was built and its always been that way ?

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