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#1
06-03-2016, 09:52 AM
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Back bow on ebony fretboard guitar
Hi! I'm a new member btw.
Acoustic guitars have become a great interest of mine in the last couple of years, and I've started to do some minor repair- and setup-work. This place has been a great source of information and inspiration for me! Now to my problem: Last November i sold an old 1960s Goya T-18 to a guy in town with no excperience in guitars. The action was good at about 3-4 mm at 12th fret, the neck had a healthy relief and the truss-rod was working nicely. The Guitar was kept with no case at about 35-40% humidity. After little over a month the guitar was brought back to me, because he was starting to have problems with fret-buzzing. I checked and saw that the neck had straightened out a bit too much, I loosened the truss-rod a tad and the buzzing got a lot better. Yesterday, about 6-months after the sale, he contacted me. The buzzing and action had now become such a problem that he sent the guitar to a luthier, the truss-rod was fully loosened. He had been keeping it in a case with a sound hole humidifier that he filled up every other day since he bought it, and the last weeks he'd been keeping it without strings on. The luthier says that it has a back bow caused by the drying of the mahogany neckwood, since the ebony fretboard has a much higher density it doesn't shrink as much, and hence causing the back bow. He says that this is a very common age related problem with ebony fretboards guitars and should be mentioned in the same breath as neck-angle issues. I've never heard of such a thing, and I've always thought that fretboards swell and straighten by excessive humidity. Neither of them agrees with me though and the luthier basically tells him that I sold him a broken guitar.. Can I have some opinions please? 
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#2
06-03-2016, 10:04 AM
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I'm no expert by any means. I agree with the sentiment, the mahogany shrinks faster than the ebony. I bet some nice 13's would pull the backbow out, with it's 90 kg of force. Tell them to string it up. Did you offer him some sort of warranty? humidity related issues should be taken care of by the owner. In any event, he should have let you check it out before he took it to someone else if he is thinking you are responsible
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disclaimer I don't know anything, everything I say is a guess, estimate, hearsay, or opinion. For your safety, don't assume anything I say is a fact. Research
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#3
06-03-2016, 10:11 AM
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All that said, six months after the sale, I wouldn't even be talking with the buyer about it. That is unless the buyer is a friend or relative, in which case, that was probably your first mistake.  Seriously, I don't see this as your problem. Further, I do not commonly (as in I can't recall ever) see the problem described with older ebony fretboards and back bow.
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#4
06-03-2016, 10:24 AM
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That's what I told them to do! I completely agree with you.
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#5
06-03-2016, 10:45 AM
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I don't see it as my problem either. The only reason I started discussing this with him was because I thought I could help him out, maybe save him some repairs. At this point it's more about me not wanting to be told I'm wrong when I'm fairly certain that I'm right  Thanks a lot!
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#6
06-03-2016, 10:55 AM
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I never heard of such a thing. Mahogany is exceptionally well stable wood. If anything the ebony will shrink and swell at a much greater rate then mahogany. Even so a neck being so narrow the rate of shrinkage usually amounts to not much. In bad cases you can see an ebony board sticking out over the edges of a mahogany neck or conversely the fret ends sticking out of an ebony board.
If the neck has back bow by nature then leaving the strings off is probably the worst thing to do for it. You may want to ask him to try a heavier set of strings.
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#7
06-03-2016, 11:48 AM
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3-4 mm action is on the high side though, and "healthy" is too vague a description for neck relief to be meaningful.
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"Still a man hears what he wants to hear, and disregards the rest." --Paul Simon
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#8
06-03-2016, 12:06 PM
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#9
06-03-2016, 12:25 PM
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The action was what I would call "medium". Perhaps closer to 3 mm than 4. These old Levin-made guitars have a bolted neck that makes it possible for a quick neck-angle adjustment . This one had som weird non-adjustable individual plastic pins instead of a saddle, and these were already filed down low, so when adjusting the neck angle i chose to be on the safe side and leave a little bit of playroom for the buyer himself to lower the action more if desired. As for the relief I don't have anything to measure it with, so I just go with eyes and on feeling for the moment. I should probably buy something What number should one strive towards, regarding relief?
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#10
06-03-2016, 01:08 PM
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__________________
"Still a man hears what he wants to hear, and disregards the rest." --Paul Simon
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#12
06-03-2016, 06:39 PM
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All the replies above are IMO correct and I cannot contribute more on that front
However, and not likely the issue with this one, but just to be aware off. When fretting an ebony neck, your fret slots need to be generous but still hold the fret, with rosewood or maple you can have a tight fret slot and just bang them in with very little issues, with ebony as its a very hard wood. Fretting the neck on tight slots, by the time you have fretted the whole way down the board, the neck will have extreme backbow, just something to consider when working with ebony boards. Steve
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#13
06-04-2016, 02:29 PM
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I guess I’m the problem discussed here. Mistakes are valuable feedback to learn from.
Firstly, I must say that I´m a complete beginner in the field of guitars (actually one of the things Sumasar was pretty accurate about) and their constructions but I find it really fascinating and I have learnt a lot since I bought this Goya T-18 from 1967 for almost six months ago. Respect to all you people out there who is sharing valuable knowledge and experiences in this area. I´ve been playing guitar since early 80s for myself in some kind of meditative purpose I guess, but never given the instrument itself much attention, and my cheap Yamaha seems to me to be insensitive to fluctuations in humidity and temperature. I had never heard terms like action, bridge, nut, neck relief, humidifier etc., at least not in this context. But I try to learn, and I find it very interesting. My old Yamaha plays ok and I bought this Goya (the subject of this discussion) just because I thought it would be nice and cool to have a Swedish made guitar from the year I was born, 1968. The Goya turned out to be from 1967, but what the heck, pretty close. And yes, I am from Sweden. Secondly, I don’t consider this problem to be Sumasar problem. I’m the one having a guitar that wont play, so it’s my problem. Since Sumasar buys and sells guitars I asked him if he wanted to buy the guitar back, but he wasn’t interested. That is that, case closed. No hard feelings. I am not holding Sumasar responsible for the playability of the guitar; I only want to understand why this has happened so it can be avoided in the future, if possible. If I have stored the guitar in the wrong way then I will be glad to learn how to do so properly. In order to find a probable cause of this back bow I will provide you with further details and some clarifications in Sumasar´s story, which I guess serves his purpose. I bought this 1967 Goya T-18 in December 2015, and he had recently bought and imported it from USA and after a neck reset, cleaning and some adjustments he sold it to me. We both live in northern part of Sweden, which is a half-year of low temperatures and very low humidity. During these six months I have owned the humidity has been around 17-27% and the temperature 20-21 Celsius (70 Fahrenheit) in the room where the guitar was kept. Thanks to Sumasar, I instantly bought a guitar humidifier (I didn’t even know these things existed back then), an Oasis OH-5 Plus+. I have always, except when playing, kept the guitar in a locked case with the humidifier inside. I have refilled it according to instructions from Oasis, not excessive as Sumasar describes it. The action has been low (but ok) ever since I bought the guitar and Sumasar showed me how to release the truss rod after four weeks to get rid of some fret buzz. I measured the neck relief in March, which was just below 0.2mm, action on low E were 2.0mm and high e 1.8mm. I tried to loosen the truss rod to increase the action a bit, but the neck was not affected even though the truss rod was completely loose. (Interesting to read that Sumasar found the relief healthy without measuring it and not knowing the measure of a good relief) No, I didn’t keep the guitar without strings for weeks, only for two days before sending it to a luthier. The reason for sending it was to improve function and looks of the bridge and saddle. (See picture below) I removed the strings 27th May just for one reason, trying to inspect the bridge plate since the low E-string popped out the weekend before. I’ve read about shipping a guitar with or without loosened strings and decided not to restring the guitar before sending it away. Don’t know if it was the right thing to do. I sent the guitar to a luthier with a good reputation who I found after searching some Swedish guitar forums. (Local luthiers are rare as dinosaurs where I live) There was no warranty on this guitar, and I didn’t consider Sumasar to be responsible for anything, which is why I didn’t send/return it to him. Two days after sending the guitar the luthier called me back and told me that the truss rod couldn’t be used to increase the relief because of a back bow on the neck, probably caused by aging and that the guitar perhaps needed some serious repairing to be playable again. I have very limited knowledge in this area, I’m still learning and I don’t question your ideas here. So don’t get me wrong when I raise these three questions. If, in this case, this back bow is a result of high humidity: 1. Wouldn’t there be other signs of a wet guitar? (http://www.acousticfingerstyle.com/humdity.htm and https://www.taylorguitars.com/sites/...aWetGuitar.pdf) 2. Is it possible that the Oasis OH-5 Plus+ humidifier can cause over humidification under these conditions and following instructions? (17-27%, 70 degrees Fahrenheit) 3. Any suggestions on how to store the guitar in a more proper way to avoid dry or wet guitar? I tried to do it the right way, but seemed to end up doing it wrong. By the way, the luthier will string the guitar with 013 strings, hopefully the neck responds well to that. Below are some pictures taken just after a took the strings off.   
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#14
06-04-2016, 03:27 PM
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[QUOTE=Sumasar;4958807] ....The Guitar was kept with no case at about 35-40% humidity...... the guitar was brought back to me, because he was starting to have problems with fret-buzzing. I checked and saw that the neck had straightened out a bit too much, I loosened the truss-rod a tad and the buzzing got a lot better......and the last weeks he'd been keeping it without strings on...... [QUOTE]
theProblem, kudos on the mature attitude of not blaming the seller. Acoustic guitars require some knowledge and maintenance, especially in difficult northern climates (I lived in Alaska for many years). The better the guitar, the more care it needs as a general rule. 35-40% humidity should be fine, stored in the case or not. The top might sink a bit as it gets drier, lowering the action and contributing to buzzes, but 35% RH should not be extreme enough to make the neck bow. The top will likely crack long before the neck is greatly affected. If the guitar is wet or over-humidified, the top will raise or swell, thereby raising the action. Many players have a shorter "summer" saddle for humid summertime weather when the top swells, and a taller "winter" saddle for when the top sinks during dry times. That saves multiple seasonal adjustments back and forth, constantly chasing good action / set-up. Taylor has a good tech sheet on truss rod and symptoms of wet and dry guitars here: https://www.taylorguitars.com/suppor...od-adjustments https://www.taylorguitars.com/suppor...tar-humidifier The real danger sign in what I read above is that the truss rod exists to offset or counteract the tension of strings. If the strings buzz, that means the truss rod should be tightened to get more relief or curvature, not loosened. If you remove the strings for any appreciable period of time -- more than a day or two -- it is best to also loosen the truss rod, to avoid excess back bow. (Count the turns or the exposed threads as you loosen the nut so you can easily return to the original condition). Left in that unbalanced state of tension for too long, the neck wood can take a permanent "set". Maybe a permanent set would take weeks or months rather than days, but I would not risk it. Most of what this "luthier" has reportedly said should be taken with a huge grain of salt (a kinder way of saying he does not seem to know what he is talking about). Maybe something was lost in translation, but I do not have a warm & fuzzy feeling about his opinions. He certainly would never get to touch one of MY instruments. Since this is an old guitar, it is unlikely that the wood suddenly settled or did anything weird that quickly. The wood has had 50+ years to get used to being this guitar. Go ahead and put 13's on it, and adjust the truss rod accordingly for minimal relief (bow). If there is still back bow, it might be time to either tune those up a half pitch for a bit of added tension, or go to even a heavier gauge set (within reason). D'Addario EJ-18 is a "heavy" set with 14-59 gauges. I use them on several guitars, but tuned down to match the tension of mediums or even lights.
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#15
06-04-2016, 03:38 PM
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Tell your luthier to put the guitar in a jig, heat the fretboard either with infra red lamps or a heating blanket, and use the jig to put a forward bow in the neck. The glue between the fretboard and the neck will slip, and when the glue cools, the neck will have lost its back bow. This is the least invasive solution (assuming prolonged exposure to a drier environment has no effect).
The neck may in the fullness of time resume its back bow ... and then again it may not.
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