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  1. #1

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    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

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    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

    FRETS.COM Field Trip

  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.

  6. #5
    Quote Originally Posted by vejesse
    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.

  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.

  9. #8

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    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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    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

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    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
    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!)

  16. #15

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    Gibson electric archtops(and I'm guessing, Zina's Ibanez copy) have laminated tops, with kerfed braces. It's not uncommon for a brace to fail(crack, and/or separate from the top) allowing the top to sink under string tension. The first thing to look for is a failed brace, using an inspection mirror through the soundhole, or through one of the pickup holes, after removing a pickup. It's not necessarily that big a job, to reglue the brace, and add reinforcement(having done it, on an early '60's ES-225), if one has the tools.

  17. #16

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    I would buy one of these in a small version:



    (Don’t know what’s it called in English, cable tensioner?) The small ones only cost a few $$.

    Attach small wooden blocks to the ends (or replace the eyes with bolts) and slowly raise the top while keeping it moisturised. Will take a few weeks or months perhaps.

    After that any loose or broken braces need to be repaired of course. And/or put a sound post to prevent sinking in the future. (Yeah I know I am preaching the use of the sound post, but it really saved my bracing-less ES-125!)

  18. #17

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    Aliphatic resin glue('Titebond' brand, yellow in color) should work fine for regluing cracked or loose braces. But it's not a job for the inexperienced, or someone unfamiliar with the tools and techniques(it would be easy to make things worse).

  19. #18

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    Quote Originally Posted by Ray175
    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.
    thats great , to give the old guitar a new lease of life .....
    i wasn't aware of the stew Mac brace or the cable tensioner ideas

    You mention the acoustic projection has actually improved
    with the brace in .... !

    is it now louder now acoustically ?
    Has the tone electrically changed much ?
    Also is the guitar noticeably any more (or less) prone to feedback ?

    This is fascinating to me
    many thanks Ray

  20. #19

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    Quote Originally Posted by Little Jay
    I would buy one of these in a small version:



    (Don’t know what’s it called in English, cable tensioner?) The small ones only cost a few $$.

    Attach small wooden blocks to the ends (or replace the eyes with bolts) and slowly raise the top while keeping it moisturised. Will take a few weeks or months perhaps.

    After that any loose or broken braces need to be repaired of course. And/or put a sound post to prevent sinking in the future. (Yeah I know I am preaching the use of the sound post, but it really saved my bracing-less ES-125!)
    Ah, I learned it's called a turnbuckle!


  21. #20

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    Quote Originally Posted by Zina
    As for humidifying... I asked someone with a bath if I could leave it there. I meant hanging it safely from the ceiling, but she started to fill the tub, ready to dunk the guitar in there!
    I think a small saucer or cup inside the guitar to hold a wet sponge will be sufficient. You don want to humidify the neck!

  22. #21

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    Quote Originally Posted by pingu
    thats great , to give the old guitar a new lease of life .....
    i wasn't aware of the stew Mac brace or the cable tensioner ideas

    You mention the acoustic projection has actually improved
    with the brace in .... !

    is it now louder now acoustically ?
    Has the tone electrically changed much ?
    Also is the guitar noticeably any more (or less) prone to feedback ?

    This is fascinating to me
    many thanks Ray
    Hi Pingu
    No perceptible change to electric tone, but pickup hight obviously needed adjusting, once the top had been raised. As far as feedback is concerned I don't play at volumes where this could happen and when I did, body position and amp orientation usually solved any potentiel problems.

    Acoustically, mid and bass response has a little more "bark", difficult to quantify by an A/B approach, but I would guess around 10%.

    Hope this helps
    Ray
    Last edited by Ray175; 10-21-2019 at 01:48 PM. Reason: Incomplete

  23. #22

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    Quote Originally Posted by Little Jay
    Ah, I learned it's called a turnbuckle!
    yes it looks like it’s buckling !yeah i know it’s the photo

  24. #23

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    Quote Originally Posted by vejesse
    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.
    i'm primarily a classical bass player, so i have some experience with this

    the luthier I go to is at this point an old friend and i've been in and out of his workshop many times over the years. re-shaping sunken tops is quite common, and i've seen the plaster molds being used quite a bit.

    I could be wrong but i don't believe it is standard procedure to thin the top - I am pretty sure the mold is made of the top as is, and then altered to reflect the desired (original) arching. The top plate is them steamed into place and set on the mold with pressure (i've seen heavy bags of what look like small metal pellets used to weigh the top down into the mold.) I'm sure it sits there to dry/set for a significant amount of time.

    Not that the procedure really matters much outside of being interesting, and amazing what a skilled luthier can do to restore a multi-century year old instrument to its original glory.

    all this is to say that folks with experience can and do perform these procedures all the time (well, on old upright basses at least.) It is a lot of work, but I have never gotten it done so I can't comment on the cost.

  25. #24

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    I can assure you that the center of a bass top is often thinned to about 3mm when the top is pressed into the mold during arching correction. Bass tops are around 8 to 9mm or even sometimes more in the area of the bridge, and despite a lot of heat, moisture and pressure it's pretty tough to get spruce that thick to change shape without cracking. Maybe the luthier you know has a way of gradually making minor mold corrections over time, but thinning any wood you want to change the shape of is common and there's no special difficulty there. The reinforcement or doubling added later keeps the new shape in place.

    Often times the deformation happens in the bridge area because the top is too thin there already, so you'll have no choice other than to install a patch which requires thinning and prepping the patch bed. The other area that will commonly deform is at the bottom of the bass bar and that area is thinner - 5mm or 6mm, so you can get away without thinning there.

  26. #25

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    There is a nice 1966 Gibson ES125CD for sale nearby. Graded player. Original electronics. Neck reset done. One stabile minor crack.

    ’But’ no 1: narrower and thinner neck that I have used to.

    Big ’but’ no 2: it has a ’sunken but stabile top’. No cracks in the braces. Former owner had ot for 15 years and top didn’t sink more.

    So what would You wise men say, will the top be stabile for long?

    Asking price is 2,5K €. (2,7K in $.)

  27. #26

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    Nice guitar, easy to play and sounds nice.

    Can sunken tops be fixed?-d58e86d6-ed11-4882-af2c-6ecda7b12dcf-jpg

  28. #27

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    I wouldn't buy a guitar with a sagging top. However, does the top really sag? Some Gibson archtops have two top points with a flat area between them. Judging from your photo, it doesn't seem as the bridge saddle is screwed up high, like it would have been if the top was sagging severely. But check it out thoroughly, including a mirror inspection of the inside (the condition of braces). As for the narrow nut, I don't like it (I'm used to 1.75" nut width) but that's a matter of personal taste. Kenny Burrells old faithful Super400 has the narrow 1960s neck and it hasn't prevented him from making outstanding music with it.

  29. #28

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    op mentions it has had a neck reset...that's reason why bridge isn't jacked high...they angled the neck in the reset to make up for the sinking top...doesnt mean the top won't sink further...lighter strings and a post under the bridge might help delay any further angle problems..hard to tell from a pic


    luck

    cheers

  30. #29

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    Quote Originally Posted by neatomic
    op mentions it has had a neck reset...that's reason why bridge isn't jacked high...they angled the neck in the reset to make up for the sinking top...doesnt mean the top won't sink further...lighter strings and a post under the bridge might help delay any further angle problems..hard to tell from a pic
    luck
    cheers
    Of course! One thing leads to another! You are genius!

    Adding the narrow nut and huge price I think I’ll skip this one.

    Thanks everybody!

  31. #30

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    I think the only way to prevent further sinking is to install a sound post under the bridge.

    After that it’s probably a great guitar but I find the price too high for a sunken top guitar..... I would do it for a $1000 less!
    Last edited by Little Jay; 05-06-2020 at 01:57 AM.