Guitar repair

[Joe Shmoe]

I've got a 1970s acoustic guitar, the constant pull of strings has lifted the bridge and given the guitar a belly in the top, probably around 4mm.

Ive removed the bridge successfully, but now need to reduce the belly before reattaching.

There seems to be quite a few YouTube videos showing repairs made using belly reducer tools, which are basically bits of aluminium which are heated up and clamped in place. I can't afford those, so does anyone have any advice of how I can straighten the top of the guitar?

Thanks for any help.
Joe

 

[Jacob]

I wouldn't attempt it at all unless it's actually coming adrift.

 

[NazNomad]

Wet paper towels, a steam iron and clamps... but if you don't know what you're doing, don't even try it.

Are you certain that it doesn't need a neck reset?

 

[thetyreman]

I would personally only let a master luthier look at my guitars, and no-one else.

I've been playing guitar now almost 20 years and never had a problem like this, maybe it's how you have been storing the guitar? I keep mine in a hardcase.

have you checked the neck for twist? I know a twisted neck is going to be a huge problem

 

[Ttrees]

Firstly... You haven't mentioned if its a solid top, i.e a bookmatched piece of spruce or cedar or redwood .
Not an extremely thin veneer of spruce over other lamination's of whatever.
You can check this with a flashlight inside the guitar, the light should be telegraphing through .
You can also follow the grain lines to the edge of the soundhole .sometimes it really looks like a solid top by some trick of the eye.
If it is indeed a solid top guitar ,then how is the center seam holding up ?

BTW There's a lot of players that look for a bellied top .
The Thompson belly reducer is only really for a severe belly caused from too heavy a gauge of string on a lightly built guitar (mostly)
Or a guitar that was left in a hot place with tensioned strings on for some time .

How much meat is there left on the heel ? has it been reset before ?
Is there signs of the ski-ramp phenomenon where the fretboard meets the body .

How did you come to the conclusion that the belly is 4mm ....i.e what reference were you using to guess 4mm ?...
which would not be terrible even for a new guitar .

First things first though, stick a straight edge on the neck ...say 24" long
so its touching all the frets ...can you bump it against the bridge ....
It should not hit the bridge at all, and depending how floppy your top is ...how much it will belly with string tension applied
That's how high it should be above the bridge .
90% sure this is your problem and you need to do a neck re-set
Plenty of new guitars in the shops that would be miles off the specifications of a Martin regarding neck angle and so on .

BTW if it is NOT a solid top and you do decide to do this ...it probably won't be a dovetail joint just some dowels and maybe a spline each side of the truss rod
and you get to guess the type of AMG (Asian mystery glue) used along with how many dowels is in there ! (hammer)
On Laminated guitars Ive used a hair dryer in the past to pull the neck off ...its not without the risk though
but if its a laminate its not worth anything anyway so you've got nothing to lose other than a guitar that wont play right in the first place
And bridges do lift off often enough anyway ....Did it come off clean you might be able to tell if its solid that way aswell ...
Shoot some more questions if ya want

Have fun Joe

 

[MrTeroo]

I took a 12 string Yamaha with a belly problem to my luthier a couple of years ago.

I waited and watched while he fixed it and this is what he made.

Only took him 1.5 hours

 

[morturn]

Joe

Are you sure that this “belly in the top” of around 4mm is a fault?

I build my acoustic guitars with a sound board radius of 24 feet, and a 15-foot radius on the back.

Assuming you have removed the strings, I would get a mirror and a torch and take a good look around inside and check all the sound board braces are still attached and not broken. Take a good look at the bridge patch too.

There are some people who build flat guitars and a few mass-produced guitars too.

 

[selectortone]

Acoustic guitars have a radiused top to allow the wood to swell and contract with changes in humidity. If a guitar had a perfectly flat top there would be nowhere for the wood to go with humidity changes and the wood is likely to split. Where you have a problem is when the bridge tilts forward with string tension causing an excessive bellying up behind the bridge and a dip between the bridge and soundhole. This is something that needs to be addressed by a competent guitar repair technician and is unlikely to be cost-effective for less expensive instruments.

 

[MrTeroo]

Acoustic guitars have a radiused top to allow the wood to swell and contract with changes in humidity. If a guitar had a perfectly flat top there would be nowhere for the wood to go with humidity changes and the wood is likely to split. Where you have a problem is when the bridge tilts forward with string tension causing an excessive bellying up behind the bridge and a dip between the bridge and soundhole. This is something that needs to be addressed by a competent guitar repair technician and is unlikely to be cost-effective for less expensive instruments.

Sorry I have to disagree.

The repair to my guitar cost £80 and it is still going strong two years later.

It was done by a professional luthier.

 

[iNewbie]

For your pleasure - Dan Erlewine and a Bridge as mentioned above:

http://www.stewmac.com/How-To/Trade_Sec ... r_top.html

 

[bigbob1]

I would take it to a luthier I only have one acoustic in my collection the rest being solid body electrics Gibson and Fender and would have no quarms about repair if needed including the electrics but acoustics are in an other league and deserve the attention of an expert.

 

[thick_mike]

Have a look inside under the bridge with a mirror, or mobile phone, there is a wooden plate with the grain running perpendicular to the soundboard grain. This can become distorted over time with the tension of the strings, of work loose. You can replace this, but it can be difficult to remove.

Frets.com has tons of brilliant advice on guitar repair.

http://frets.com/FretsPages/Luthier/Tec ... rplt1.html

http://frets.com/FretsPages/Luthier/Tec ... uebr1.html