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  1. #1

    Can sunken tops be fixed?

    I have a 1934 Gibson L-75 (Gibson L-75 1934 | Acoustic Music) that has a sunken top between the bridge and the neck, but more on the bridge side. It sounds and plays great with reasonably low action. Partly because the neck angle is also off, just enough to compensate for the sunken top (this may take a moment to visualize).
    When I got it last year it had badly worn frets and a small crack on top. I got it repaired at one of the top repair shops in the city. The repair person confirmed that the top is sunken but he said he had never repaired a sunken top and suggested that a violin repair shop could be able to tackle that.
    I really like the guitar, if I decide that it's a keeper I'll like to get the top (and the neck) repaired as currently the bridge is in the lowest position and the tail piece is almost in contact with the "unsunken" part of the top.
    I looked inside of the guitar with a small mirror, braces are kerfed but they are intact, nothing broken. Seems like kerfed braces aren't strong enough to hold the sting load and caved in gradually.
    Does anybody have experience with this situation? Can it be fixed? Would the fix affect the sound? Would it be too structurally intrusive for an 87 year old guitar? Even if fixed, would the fix be reasonably permanent?

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  3. #2
    I had a Barney Kessel Custom that had a sunken top. In a complicated story, I wound up trading it to a guitar store for a much lesser guitar. The repairman razed the entire top, and then re-finished it, and had it on sale for over 2K. I bought it used for about $450.

    I played it after he finished it, and I hated the way it sounded.

  4. #3
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    Yes. See this article

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  5. #4
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    If you wanted to repair this like they would in the violin world here's what's involved: removing the top, making a plaster mold of the top, removing the braces and thinning the top where you want to change the arching, altering the mold to reflect the original arching when the guitar was new, pressing the top into the corrected mold with heat and pressure, installing a "belly patch" to lock in the new shape, then fit new braces. Then you'd be looking at a neck reset.

    Sounds like a lot of work.
    Luthier - The Double Bass Workshop

  6. #5
    Quote Originally Posted by vejesse View Post
    If you wanted to repair this like they would in the violin world here's what's involved: removing the top, making a plaster mold of the top, removing the braces and thinning the top where you want to change the arching, altering the mold to reflect the original arching when the guitar was new, pressing the top into the corrected mold with heat and pressure, installing a "belly patch" to lock in the new shape, then fit new braces. Then you'd be looking at a neck reset.

    Sounds like a lot of work.
    Thanks, that makes sense. Yes, it's a lot work. I wouldn't even attempt that which than would mean a lot of money I am guessing 1 or 2 grands? Considering that I got it at a reasonable price, guitar might be worth that. It'll certainly improve it's playability especially in the long run. My fear is if it would have a negative effect to it's sound.

  7. #6
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    Well, there's an easier way, also in the world of orchestral strings, assuming that the top does not sink when there is no tension on it:
    - Remove the back of the guitar. Keep the old binding.
    - Reinforce the braces (as per Frank Ford's method) - replacing them is probably too much $$$
    - Replace the back/binding
    - Reset the neck
    Worth getting costed by a local violin repair shop.
    Or decent guitar repair shop.
    Properly done, the fix would be permanent.
    "Somebody get me out of this chair." - BOB WILLS
    Hammertone is a registered Hofnerologist.

  8. #7
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    In the violin repair world, unless the back is already partially loose it's only removed if necessary. If you need to get inside the instrument generally it's much easier and less damaging to remove the top, and much work can be done on the back even if it's still attached. In the world of acoustic guitar, the back rather than the top is typically removed especially if the neck is still attached. For this job if you remove the neck first I'd consider removing the top instead, that way you get at the braces directly. Or, it might be best just to glue the braces as best you can through the F holes and reset the neck.

    If you're actually going to go through the trouble of opening a guitar and doing all the accompanying work with binding and finishing, refitting some braces seems like the least of your problems. As long as you're in there do everything that's needed so you don't have to open the guitar ever again.

    The reason I mentioned the violin top reshaping is that the original post mentioned a violin shop potentially working on an instrument with a sunken top. If you want to go "all the way" that's how you go about it but guitars are a different animal. They're not really meant to be taken apart easily.
    Luthier - The Double Bass Workshop

  9. #8
    The luthier I had working for me at the shop fixed a few that were sunken. It took many months to fix but no refinish was needed and if you didnt know the tops had been sunken ,you could not tell. It involved varying the humidity while sticking a post under the sunken area and after a few weeks he would shim the post a tiny bit and increase the humidity a bit repeating this for however long it took, I know it took over a year to fix a 175 and there were zero signs of anything having been done. I dont recall what model the other one was but that took almost as long. the key is to crown the top of the post to the correct curve of the top. Bob

  10. #9
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    Gibson ES-125 Sunken Top

    I bought a 1954 Gibson ES-125. The top had 'sunk' quite badly, to the extent that the neck angle is far greater than it should be.
    I took a look around inside (using a flexible USB camera), and it was clear that this problem had been 'repaired' before, but not well
    New arch braces had been made to the already sunken shape, and reglued. One of these has since parted away from the top.
    Anyway, I removed the lower binding and the back of the guitar to confirm the situation, and it is now apparent that the last 3" of the fingerboard (the part overlapping the archtop deck) has warped with the deck, making the mid-neck action way too high. Even lowering the bridge drastically will not solve the problem.

    My idea is to use the back (which still has its great 'shape') to create a caul, and then use that from the inside to try to re-shape the top plate using gradual pressure, mild heat and mild humidity (probably over a period of months). Once the 'arch' is restored, I'll make new bracing stringers and glue them in, and then add a cross-brace to the back immediately below the bridge position to provide a footing for two 'sound posts' (as used in violins). (The idea for the soundposts came from other discussions about tone and reducing feedback).

    Any ideas, comments, advice?

    Thanks, Noel

  11. #10
    One question is if there is a risk of a highly aged top losing it's stiffness after being reshaped. I'm guessing that the chemical properties of aged wood is quite different than that of fresh wood. My concern is that the reshaping may cause a lot of micro cracks in the already crystallized wood fibers. I mean this may all be bollocks, I am completely arm-chair speculating here. But it doesn't seem completely in-plausible. Any thoughts?
    Last edited by Tal_175; 12-11-2018 at 11:22 PM.

  12. #11
    Some of the mid-30’s Gibsons such as the X-braced L-7s were carved with a top shape that looks somewhat sunken, but isn’t. You might check whether L-75s are similar.

  13. #12
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    After moving to 14s this summer, the top of my 1961 ES175D began to sink perceptibly and the bridge had to be raised significantly to compensate.

    As a makeshift/temporary solution I removed the pickups, and inserted an adjustable brace from StewMac to raise the top to its previous height. When I'm next in the UK with a car I will take it to Gordon Wells at Knight Guitars to see what he suggests. I'm leaning towards to Frank Ford's method.....

    Having said that, for the last 4 months it has held up perfectly, and acoustically the guitar's projection and resonance has improved massively - go figure!

    I'm currently considering putting a temporary sound post in place of the (heavy) adjustable brace for the time being.

  14. #13
    Quote Originally Posted by KirkP View Post
    Some of the mid-30’s Gibsons such as the X-braced L-7s were carved with a top shape that looks somewhat sunken, but isn’t. You might check whether L-75s are similar.
    Good point, but unfortunately the guitar tech confirmed that he top is sunken last year when I got it refretted. His reasoning very convincing. The pointy part of the f-holes aren't in the same plane with the body.

  15. #14
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    Consider a sound post!

    The small sound post in my ES-125 has been keeping the arch in perfect shape - no sign of sinking whatsoever.

    Granted, I don’t use heavy strings: TI Swings .012 with a 0.013 high E but then again: my ES-125 has no bracings at all anymore (!). (How that happened still puzzles me... they must have become unglued and a former owned took them out, which can’t be done without breaking them or chopping them up... ough!)

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