CSHar Posted April 7, 2019 Share Posted April 7, 2019 I have a 1947 Southern Jumbo with what seems like an excessive amount of top deflection (measured behind th bridge for the center to the edge at the kerfling). The deflection measures 0.29” (around 5/16). It has had a recent (3 months ago) neck reset, new bridge plate, new bridge, slight shaving of the cross braces. Everything appears to be functioning without any cracks or separations. recently hydrated it using a moist sponge in a dish on the inside for about 4 days. The bulge has been obvious but the hydrating may have lifted it slightly more. Any thoughts on what would be a normal amount of top deflection on this type of guitar. Link to comment Share on other sites More sharing options...
jedzep Posted April 7, 2019 Share Posted April 7, 2019 Can you let that beast dry out slowly in a 50ish %RH? It might settle down. Nick will chime in on the belly. My J50 has one. Beware the humidifying trinkets that aren't dialed in. Tune down a step for a bit and talk to the luthier who did the work. Nice guitar, huh? Link to comment Share on other sites More sharing options...
j45nick Posted April 7, 2019 Share Posted April 7, 2019 My "new" 1950 J-45 (FON 3358, as opposed to my "old" 1950 J-45 which is 3644) has a top dome of somewhere between 5/16" and 3/8" both transversely and longitudinally. There is no dip in the top forward of the soundhole--it's an almost even dome overall, with the bridge sitting at the high point. My luthier, who just finished a neck re-set and other work on it (I'm picking it up next week) didn't think it was particularly excessive. Apparently, a lot of older Gibsons and Martin dreads were built with a lot of dome in the top, in addition to the typical arch of about 3/16" on the bottom for the Gibsons. (he works on a lot of vintage Martins and Gibsons, including the really good stuff.) FON 3358 lived under a bed in Youngstown, Ohio, from 1951 until I bought it a few weeks ago, so it has seen huge variances in temperature and humidity in that environment. Not a single crack in the top or body, and only modest lacquer checking. Top braces, bridgeplate, and bridge were all tight. Four back braces needed re-gluing. Go figure. I'll look at it more carefully when I get it back. The plans for the 1957 J-45 show a top and bottom dome of about 3/16" both longitudinally and transversely. Link to comment Share on other sites More sharing options...
CSHar Posted April 7, 2019 Author Share Posted April 7, 2019 Can you let that beast dry out slowly in a 50ish %RH? It might settle down. Nick will chime in on the belly. My J50 has one. Beware the humidifying trinkets that aren't dialed in. Tune down a step for a bit and talk to the luthier who did the work. Nice guitar, huh? Thanks. Yes it has a wonderful bright tone Link to comment Share on other sites More sharing options...
OldCowboy Posted April 7, 2019 Share Posted April 7, 2019 My "new" 1950 J-45 (FON 3358, as opposed to my "old" 1950 J-45 which is 3644) has a top dome of somewhere between 5/16" and 3/8" both transversely and longitudinally. There is no dip in the top forward of the soundhole--it's an almost even dome overall, with the bridge sitting at the high point. My luthier, who just finished a neck re-set and other work on it (I'm picking it up next week) didn't think it was particularly excessive. Apparently, a lot of older Gibsons and Martin dreads were built with a lot of dome in the top, in addition to the typical arch of about 3/16" on the bottom for the Gibsons. (he works on a lot of vintage Martins and Gibsons, including the really good stuff.) FON 3358 lived under a bed in Youngstown, Ohio, from 1951 until I bought it a few weeks ago, so it has seen huge variances in temperature and humidity in that environment. Not a single crack in the top or body, and only modest lacquer checking. Top braces, bridgeplate, and bridge were all tight. Four back braces needed re-gluing. Go figure. I'll look at it more carefully when I get it back. The plans for the 1957 J-45 show a top and bottom dome of about 3/16" both longitudinally and transversely. I tend to concur. My '42 J-45 exhibits a lot of dome, which I've been told by 'old folks' who worked at Gibson Kalamazoo is typical. Also, my '51 SJ exhibits a similar dome, as did my, now departed, 1950 J-50. Link to comment Share on other sites More sharing options...
Leonard McCoy Posted April 7, 2019 Share Posted April 7, 2019 You ask how much belly bulge be acceptable. The short: as much as the structure and playability of the guitar allow without the bridge popping off, or the guitar and its internal structure ripping apart. In terms of top projection a domed top is desirable. In fact, most high-end guitars, vintage or brand-new, will display some form of bellied top, taking into consideration also that (Gibson) flat tops usually aren't perfectly flat to begin with but starting out as slightly radiused top for that very same reason. The other question you gotta be asking is whether you can do anything about it. The short: not really. Once wood takes to a certain shape or form, it likes to stay that way. Even if you force it out of that form, eventually it will revert back to it. You just gotta watch out that you don't worsen the issue by your experiments. Link to comment Share on other sites More sharing options...
j45nick Posted April 7, 2019 Share Posted April 7, 2019 You ask how much belly bulge be acceptable. The short: as much as the structure and playability of the guitar allow without the bridge popping off, or the guitar and its internal structure ripping apart. In terms of top projection a domed top is desirable. In fact, most high-end guitars, vintage or brand-new, will display some form of bellied top, taking into consideration also that (Gibson) flat tops usually aren't perfectly flat to begin with but starting out as slightly radiused top for that very same reason. The other question you gotta be asking is whether you can do anything about it. The short: not really. Once wood takes to a certain shape or form, it likes to stay that way. Even if you force it out of that form, eventually it will revert back to it. You just gotta watch out that you don't worsen the issue by your experiments. What Leonard says. If everything in the top is tight, and there is no distortion such as a tilting bridge or downward top deflection forward of the bridge and around the soundhole, there isn't much you could or should do about it. In the case of my J-45 3358 ("Youngstown", as opposed to 3644, which is nicknamed "Jackson"), you can see that the transverse top radius is carved into the bottom of the bridge, so it must have been built that way. There was a discussion on UMGF recently about the differences in top dome/radius of vintage vs modern Martins, and someone who seemed fairly knowledgeable pointed out that the increased top dome of 1930's dreadnoughts was one reason for their extraordinary volume and projection. Tom Barnwell might comment on that, since he has a number of Martin and Gibson dreadnoughts and slope-J's from the 1930's. It may be that Gibsons had a similar history. You can pretty much tell by looking at the top bracing whether or not the top dome is the result of distortion or was built that way. A domed top is actually a lot more resistant to distortion than a flat top, for the same reason that bridges aren't flat. An arch that is pinned at the ends resists sag a lot more than a straight beam that is pinned at the ends. You have to look at the top of a guitar as a beam. Enough of the talk. Time to play. And I would really like a 1947 SJ. A birth year guitar for me. Link to comment Share on other sites More sharing options...
dhanners623 Posted April 7, 2019 Share Posted April 7, 2019 I believe it was Norman Blake who said, "Never trust a guitar without a belly." The belly bulge is built in; it's called a "loaded" top. Here's this: https://bourgeoisguitars.net/our-news/belly/ Welcome to the forum and enjoy the '47 SJ! If you posted photos, we wouldn't object.... Link to comment Share on other sites More sharing options...
zombywoof Posted April 8, 2019 Share Posted April 8, 2019 Controlling environment is not all that easy. The only way I have been able to dry out a guitar when say I want to reduce the belly is to use silica gel which takes some preparation and experimentation to get it right. There comes a point where it is just easier to drop the guitar off at the shop and let them remove the bridge and use cauls and clamps to reduce the belly. Link to comment Share on other sites More sharing options...
j45nick Posted April 8, 2019 Share Posted April 8, 2019 I had an interesting discussion today on this topic with Ross Teigen, who works on my guitars. He has been building and repairing guitars for about 40 years, and was a performer before that. He had just finished a neck re-set and other work on my "new" 1950 J-45, which has a really substantial top dome. The basic question was: what causes a guitar to need a neck re-set? is it the neck moving in relation to the body over time, the body changing over time, or some combination? The simple answer is "all of the above." Here's a summary of what he said, paraphrased: Guitars are individuals. Each piece of wood is different, even in guitars of the same model, built on the same line at the same time. Over time, they respond differently to their environment. The stresses on a guitar, primarily string tension, affect each guitar differently. It takes years for a guitar to "settle in" to its natural geometry based on the wood and the stresses applied, primarily string tension. Once a guitar has "found" its natural geometry, you may have to adjust the neck angle to the body geometry to make it more playable. You can't reasonably try to completely return a guitar to its as-built geometry: it is better to adjust the neck angle to its "final" settled geometry, provided the guitar is not structurally compromised by loose braces, bridge, bridgeplate, etc. Generally, the amount of top and back dome in a vintage guitar varies over time, so that there is no "right" or "wrong" amount. A lot of the tonal character of vintage guitars derives from these differences in body geometry compared to a new guitar, in addition to the very real impact of the aging of the wood. If you try to return a guitar to its original body geometry, it may have a significant impact on the tone. A neck re-set on an older guitar is likely to be a one-time operation. Once the geometry has settled, it doesn't change much over time after that. He said a lot more than this, but this is the gist of it. This came up because my "new" 1950 J-45 has substantially more top dome than is shown on the standard J-45 plans, and a lot more than my other 1950 J-45 (with the 1968 top). Incidentally, he also said I got lucky on timing when I brought my guitar in. If I brought it in today, he couldn't touch it until October. Link to comment Share on other sites More sharing options...
jedzep Posted April 8, 2019 Share Posted April 8, 2019 Freekin' genius. Why we love old guitars. Link to comment Share on other sites More sharing options...
zombywoof Posted April 9, 2019 Share Posted April 9, 2019 It just takes guitars a bit to figure out they are no longer trees. Link to comment Share on other sites More sharing options...
jedzep Posted April 9, 2019 Share Posted April 9, 2019 Haha. Exactly! That's the best way to put it. Baseball bats share that same dilemma. Link to comment Share on other sites More sharing options...
zombywoof Posted April 9, 2019 Share Posted April 9, 2019 J45nick's post just made me realize that I am now on my second repair guy who is second generation. They are as different as night and say though. My guy in the Middle of Nowhere Missouri did pretty much everything by hand in a shack behind his house. If you dropped an instrument off during turkey hunting season you were assured of a rather long wait. My present guy not only repairs but builds guitars so even has a CNC machine. No turkey hunting though as far as I know. Link to comment Share on other sites More sharing options...
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