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meandi

Repairing a Gibson acoustic 12-string with a crushed top

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Whatever fell to the top of this guitar was a focused blow.

You can see the V shaped impact area, where the wood is fractured across the grain, just in front of the bridge on the bass side.

crushtop1.jpg

 

Up close view of the damaged area.

crushtop2.jpg

 

Top is sunk considerably.

I laid a brace across the top & pulled the top up to straight with a clamp & left it overnight.

When I took the clamp off, the top returned to the dammaged configuration, thus has taken a "set", or has a memory, in this shape.

crushtop3.jpg

 

To compound the problem, there is a radical hump in the center of the top behind the bridge.

Bridge will have to come off as well.

crushtop4.jpg

 

To take the loads off the top for proper repair & realignment, I'm going to have to remove the bridge plate, which on this guitar is quite large, extending from behind the bridge pins to just shy of the sound hole.

It's not visable in the pic, but the impact has also left the front tip of the bridge plate seperated from & down from the top about 3/16", further necessating bridge plate removal.

This is going to be an interesting project...see if I can get it to do what I want.

crushtop5.jpg

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I'm not a luthier by any means, but that looks to be a very ominous dent. It's right at the fulcrum point and, in its present condition, is a very weak spot. 250+# of string tension is going to be trying to pull everything right into that dent.

 

You got some work ahead of you and I certainly wish you well. It looks like a guitar worth saving. Please keep us posted as to your progress. Good luck, my friend. :wave:

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I'm not a luthier by any means, but that looks to be a very ominous dent. It's right at the fulcrum point and, in its present condition, is a very weak spot. 250+# of string tension is going to be trying to pull everything right into that dent.

 

Agreed on the fulcrum point.

With string loads focused at the bridge, the behind the bridge bulge is the result.

 

Bridge has taken the profile of the top.

crushtop6.jpg

 

And, is trying to separate from the top.

crushtop7.jpg

 

Some interesting wood in the back.

crushtop8.jpg

 

You got some work ahead of you and I certainly wish you well. It looks like a guitar worth saving. Please keep us posted as to your progress. Good luck, my friend.
:wave:

 

I like projects that present situations that I haven't encountered previously.

Makes me think. :)

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Yikes, what a project! Keep us posted.

 

The thread is in real time, so you'll see it as it happens.:wave:

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I've done a little reading on their product.

It's a good concept from an engineering point of view...spreading loads etc...

Not sure they make a 12 string model.

 

I'm at a work computer that can't view the pictures (net nanny), but I can comment on the JDL bridge doctor. I had a pretty serious bulge in the lower bout of my old D12-28 and tried a 'doc in it. Because I didn't want to drill any holes in the bridge I got the kind that uses the brass "pins" with the holes in the ends for the strings. It did reduce the bulge (slightly), but the break angle was so low that those strings barely touched the saddle (duh). Took it out, got the neck reset (which was the real problem) and life is good.

 

Some people argue that if the JDL is designed into the bracing (Breedlove) that it is a good concept - but if you look at the bracing in a Breedlove you'll see that it is very deeply scalloped - they probably need the 'doc to avoid complete implosion. Most people who have tried them in ordinary guitars say that the tone is affected - and not for the better.

 

I'd say that from an engineering standpoint it makes little sense - you want the top to rock to make sound, yet this thing impeds the rocking motion along with reducing the driving force due to break angle. Your milage may vary, mine was bad.

 

I'll enjoy looking at this thread when I can see the pictures.

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Please excuse my ignorance, but couldn't a new sound board be made? I know it would probably be A LOT of work, but it seems that it would be the best fix.

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I can't get over the wood on the back of that guitar. It's beatiful. Very pronounced grain and perfectly matched. Save her! :snax:

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Back looks like Brazilian rosewood...but since the insides don't match it's obviously laminate. I didn't know Gibson made laminate guitars that often but I guess it's possible.

 

As for the repair, it looks to me like the braces have separated from the soundboard in a number of places. Here's a cool link:

 

http://www.frets.com/fretspages/luthier/Technique/Guitar/Structural/XBraceWrinkle/xwrinkle1.html

 

wrinkle1.jpg

 

wrinkle2.jpg

 

wrinkle3.jpg

 

wrinkle4.jpg

 

looseinside.jpg

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Good luck on that one.

That is some beautiful wood on there. Hope you can save it.
:thu:

EG

 

Thanks.

It is beautiful wood.

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I'm at a work computer that can't view the pictures (net nanny), but I can comment on the JDL bridge doctor. I had a pretty serious bulge in the lower bout of my old D12-28 and tried a 'doc in it. Because I didn't want to drill any holes in the bridge I got the kind that uses the brass "pins" with the holes in the ends for the strings. It did reduce the bulge (slightly), but the break angle was so low that those strings barely touched the saddle (duh). Took it out, got the neck reset (which was the real problem) and life is good.


Some people argue that if the JDL is designed into the bracing (Breedlove) that it is a good concept - but if you look at the bracing in a Breedlove you'll see that it is very deeply scalloped - they probably need the 'doc to avoid complete implosion. Most people who have tried them in ordinary guitars say that the tone is affected - and not for the better.


I'd say that from an engineering standpoint it makes little sense - you want the top to rock to make sound, yet this thing impeds the rocking motion along with reducing the driving force due to break angle. Your milage may vary, mine was bad.


I'll enjoy looking at this thread when I can see the pictures.

 

It's always interesting to get feedback from someone who has direct experience with this type product.

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Please excuse my ignorance, but couldn't a new sound board be made? I know it would probably be A LOT of work, but it seems that it would be the best fix.

 

A new soundboard could be made.

The guitar is a player & the entire focus is to get everything solidly back in it's original configuration.

The "hit" area will still be visable, but strong once the work is completed...no finish repair to be done.

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I can't get over the wood on the back of that guitar. It's beatiful. Very pronounced grain and perfectly matched. Save her!
:snax:

 

Going to give it my best shot.

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Back looks like Brazilian rosewood...but since the insides don't match it's obviously laminate. I didn't know Gibson made laminate guitars that often but I guess it's possible.


As for the repair, it looks to me like the braces have separated from the soundboard in a number of places. Here's a cool link:

 

The back does seem to be a veneer.

There will need to be some reglue on some braces.

That in-body camera that he has is the cat's meow.

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It's always interesting to get feedback from someone who has direct experience with this type product.

 

Meandi, here is another take on the bridge doc as well as some interesting work on another old Gibbie 12. This guy seems pretty happy with it.

 

http://www.premierguitar.com/Magazine/Issue/2008/Jul/New_Sound_Old_Guitar.aspx

 

In another thread we could have a great time discussing how the top moves on different types of guitars, how bracing works (this thing is just one more brace after all). Short story however is that very few people (Breedlove, this author, the manufacturer) really feel that it adds a lot to a guitar - in my case it was a disaster (the thing is in a drawer somewhere)

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Meandi, here is another take on the bridge doc as well as some interesting work on another old Gibbie 12. This guy seems pretty happy with it.


http://www.premierguitar.com/Magazine/Issue/2008/Jul/New_Sound_Old_Guitar.aspx


In another thread we could have a great time discussing how the top moves on different types of guitars, how bracing works (this thing is just one more brace after all). Short story however is that very few people (Breedlove, this author, the manufacturer) really feel that it adds a lot to a guitar - in my case it was a disaster (the thing is in a drawer somewhere)

 

I appreciat the inside info, Freeman.

I was basing my statements earlier on what I had read on their website.

It's definately not a solution in this project.

 

 

I've got a heater blanket that I use for removing fingerboards, & I've used my wife's clothing iron to warm bridges for easy removal.

Problem...that was all done on the outside of the guitar.

I need the heat inside on the bridge plate in order to get it out cleanly.

So I went shopping & found this little travel iron.

My karma is strong today, in that it's just the perfect size to fit inside the bracing around the bridge plate inside the body & the bridge plate is almost exactly the same size as the iron.

 

Had to remove the handle & strip it down to the base to have room to work inside with it.

Put a thermostat on it & it'll go to 300f...perfect.

crushtop9.jpg

 

crushtop10.jpg

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Yea I use an old clothes iron for removing bridges and fingerboards a lot.

I usually set it on the "cotton" setting which is as high as it goes.

I've found that it's better to heat the bridge slowly, especially if it's thick.

For one thing it shocks the soundboard and bridge less and you're less apt to get cracks. For another you get less chance of charring the wood and leaving a mark on its surface. The glue needs time anyway for the heat to work on it. So sometimes I will actually remove and replace the iron as I'm heating up the bridge...or start on a lower setting and then increase the heat with time. Basically that way the bridge heats up throughout uniformly instead of getting super hot just on its face.

 

I've heard of luthiers using heated knives to work into the underside of the bridge...Some actually electric...others basically a sharp wide flat knife heated with an iron on them. It seems to make sense

because you are just putting heat on the glue joint, but it always seemed slower and more of a threat to the soundboard...I've never been able to get that strategy to work for me better than just heating the entire bridge.

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Yea I use an old clothes iron for removing bridges and fingerboards a lot.

I usually set it on the "cotton" setting which is as high as it goes.

I've found that it's better to heat the bridge slowly, especially if it's thick.

For one thing it shocks the soundboard and bridge less and you're less apt to get cracks. For another you get less chance of charring the wood and leaving a mark on its surface. The glue needs time anyway for the heat to work on it. So sometimes I will actually remove and replace the iron as I'm heating up the bridge...or start on a lower setting and then increase the heat with time. Basically that way the bridge heats up throughout uniformly instead of getting super hot just on its face.


I've heard of luthiers using heated knives to work into the underside of the bridge...Some actually electric...others basically a sharp wide flat knife heated with an iron on them. It seems to make sense

because you are just putting heat on the glue joint, but it always seemed slower and more of a threat to the soundboard...I've never been able to get that strategy to work for me better than just heating the entire bridge.

 

I use surface thermometers to monitor my heat & 250f has proven to be a good temp for both fingerboards & bridges.

On the bridges, along with warming the top with an iron, I also use a thin blade that I warm with a small butane torch & work it from both sides.

 

This photo is from a couple of years ago...another 12string that I did a truss rod upgrade to double action & a refret...the thermometers can be seen on the heater strip.

 

http://acapella.harmony-central.com/forums/showthread.php?t=1539341

 

heat.jpg

 

This shot's of the same guitar when it came back, about a year later, for a neck reset.

The bridge was also lifting & I pulled it & did a reset on it as well

 

http://acapella.harmony-central.com/forums/showthread.php?t=2213015

 

reset16.jpg

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