Sunken top old As

[Br1ck]

Is the solution for a sunken top on an old Gibson A removing the back and regluing the brace under the bridge? I dabble in repair and have more time than money (retired). Thinking a project would be a good way to own one.

[pops1]

you can usually glue the brace thru the sound hole, no need to remove the back.

[MikeEdgerton]

Frank Ford has a few articles about this on his www.frets.com site:

http://www.frets.com/FretsPages/Luth...andobrace.html

http://www.frets.com/FretsPages/Luth...ndotopsag.html

http://www.frets.com/FretsPages/Luth...LTop/a4l1.html

[Tom Haywood]

Re-gluing a brace may or may not be the solution to a sunken top, but often it is. Re-gluing through the sound hole may or may not be the best solution. It's all a judgement call based on careful examination of the mandolin and the outcome you are looking for. I had one in the shop last week with a caved in top due to a loose brace. The bass side tone bar was still glued on for about 1 1/2 inches near the neck, but was otherwise completely off the top. The braces were not notched into the kerfed lining. Looking at the old glue, and realizing this mandolin had seen some heat and came to me through a high end violin shop, the only thing that made sense to me was to take the back off to be able to clean off the old glue and to carefully inspect all the braces and glue joints to achieve a solid repair. I felt that re-gluing the brace through the sound hole would not be a lasting repair because there was too much old glue that could not be removed that way, too much clamping that I wouldn't be able to see very well, and the top appeared to be pretty well warped. The owner confirmed that this mandolin had traveled the world and had seen some heat and other rough treatment, and he agreed that it made more sense to order a new one just like it from Amazon for $149.00 than to spend less than that for an iffy repair or more than that for a good repair.

So there is a good chance that it would work well for you to obtain an old Gibson A with a caved in top. But it is going to depend on the one you get.

[rcc56]

Many of them will respond to a re-glue through the soundhole, some will not. You can get some idea of how an instrument will respond by clamping it up without any glue and observing the results, sometimes even by watching as you push the brace up with your fingertip.

As far as taking an oval hole Gibson back off, it is not such a bad job as it could be, but you have to proceed slowly and carefully. I recommend you make a temporary form out of rigid foam insulation or anything else that you can find, because the sides will want to spring out of shape a little bit. Also, watch for nails between the back and the neck and tail blocks-- these were used for alignment during factory assembly and cannot be seen from the outside of the instrument.

[Jim Garber]

Is the solution for a sunken top on an old Gibson A removing the back and regluing the brace under the bridge? I dabble in repair and have more time than money (retired). Thinking a project would be a good way to own one.

Hmmmm. I am no luthier but I wonder if this is the best way to get a vintage Gibson A. I know there are many degrees of sunkenness of tops but with the amount of decent As out there without sunken tops I think you might be better off finding ones with cracks or separations. To me a sunken top is one of the more dicey propositions. My feeling is that wood has a memory and once it sinks might want to revert over time. Of course, if you get one for free or for a few hundred dollars then, I suppose, it could be sensible. Do you have a particular one in mind?

[mandopaul]

I don't get how a top that is sunken around the bridge area could respond to a brace that is only just behind the sound hole?

[rcc56]

It's rather hard to explain without going into the physics of the instrument, but it works, at least most of the time.

The brace counteracts a loss of strength in a top that is caused by the presence of the soundhole. The brace in an oval hole mandolin actually has more radius than the top, and acts like a spring. When the brace loosens up, the bridge pushes the top down because of the loss of the strength that the brace provides. When the brace is re-glued, the "spring" is restored, and its force spreads out throughout the whole of the top.

So much for the abbreviated theory. The most important thing is that we know it works.

I ought to add that even though it is easier to remove the back from an ancient hide-glued Gibson mandolin than it is from a modern Gibson guitar or mandolin, it is not an easy job. A lot of things can go wrong. Removing the back is to be avoided unless there is no other choice.

I might mention that a loose brace is very common in these 100 year old instruments, and that whenever one comes into my shop for any reason, the first thing I do when I look the mandolin over is to stick my finger in the soundhole and check that brace.

[Tom Haywood]

I think there is something to Jim's feeling that wood has a memory in this situation. More likely, the wood fibers tend to move in some direction as the plate dries out more completely, and that movement may be with or contrary to the bracing. On the mandolin I described above (an F hole mandolin), I let my fingers do the dry clamping in order to feel if the wood wanted to go back to it's braced shape. It felt like it did not really want to, which is what finally convinced me that the back had to come off. I've seen others that went back into position readily.

[Br1ck]

Just thinking out loud. No particular mandolin in mind. Thanks for the info.