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Hi gang,

I’ve got a guitar back in the shop after it spent a week or so in Phoenix AZ where the afternoon RH dipped to about 2% at 85°. The owner emailed in a panic saying that the strings were all but laying on the fretboard. Granted the setup was on the low side, 3/64” - 5/64” at the 12th and .015” - .017” at the nut, played like budda! Anyway the neck has been back in the shop for about 2 weeks, and back in Washington state for a about month with no sign of the back-bow coming out. It’s also got pretty severe fret-fang and I don’t think it’s gonna come back. The neck has 2, 1/8”x 3/8” CF rods flanking the dual action truss rod and the truss rod can just pull it back to straightish and I’m reluctant to put any more torque on it. I thought the CF would do more to force it straight again.

On the upside, there are no cracks in the body.

I’m thinking it’s time to get a new neck happening unless you folks have other ideas...

Cheers, M

If the neck is in back bow and you can't adjust it out this is yet another example of why CF augmentation in necks is not always a good idea. Not being critical of you but as a builder of dozens of guitars myself and as a repair person of over 10,000 guitars and more now I see things every day that I would do differently.

So if I understand the problem correctly Michael on this very pretty guitar the neck is in permanent back bow (a frequent occurrence of drying out we see dozens of these every Michigan winter...) and the truss rod is maxed out?

Before I go making a new neck my approach would be to relax the rod, assuming it's a two way rod so that you have maximum adjustability going forward. Relax the rod and then possibly remove some of the inlays and and all of the frets. Relevel the board, it will be big job milling that hump out of the center but that's one way to do it. Once the board is level, the neck angle is correct, you have milled in fall-away, mill in some relief in the board too less on the treble side and more on the bass side.

Now refret it and since we did all the shaping of the fret plane with the board only minimal kissing of the fret tops and recrowning will be necessary. Your "fret sprout" will be gone since we replaced those frets and the truss rod will be working again although limited in it's travel because of the CF augmentation that is not necessary or advisable on a conventional acoustic neck.

A full refret is a larger service for us and I would charge this client this is not warranty this is abuse to let an instrument dry out like this. We are a Martin warranty center and we would reject this claim as warranty especially with the obvious tell tale of fret sprout.

You may have to mill away enough of the board to go though some of the middle inlays so that's why I would be keen to maybe remove those and reinstall later. If the back bow is severe that leveling the board would look funny making the fret board thin in the center it's new neck time.

All up a new neck is a BIG deal and for a profitable, busy repair shop with everyone on a waiting list now to make a new neck that could be a $2K thing for us. Refretting it will cost your client around 1/4 of that, be much faster with no finish to wait to cure and be as good as new.

Now how do we instill in this client that he has to do better with taking care of his guitar? Small humidified room, case humidifier, etc. It's always part of our challenge to help our clients avoid this in the first place. Any guitar going to Arizonia from any maker be they a f*ctory or an individual should always carry warnings and disclaimers about the ravages of RH, etc.

Michael if you have any questions and want to PM me I am happy to help. There are a number of members here who I'm in touch with nearly every day helping them with repairs, etc.

PS: Did I mention that this is a very pretty guitar! Nicely done.

Thanks Hesh,

He was warned which prompted his purchase a hygrometer and a humidifier for the body before he left for AZ. This of course did nothing to save the neck, but likely saved the body. He knows he messed up bad and is willing to pay whatever it takes to make it right again.

Do you have a recommendation for a case humidifier of some sort?

I'm sure I speak for many here when I say Thank You for all you contribute to this forum!

I will ping you if I get stuck.

Best, M

Hey Michael - Yes we like the Ossis OM-1 case humidifier and sound hole humidifiers and send them home with our dried out guitar clients. I used to include one with every guitar I built and sold not only to protect the guitar but so I could protect myself from unwanted liability if someone claimed we never had an RH conversation.

The D-Addario pack system costs a bit more and it tested the best of all of them with Dave's tests that he did. That's a great choice too but the user does have to understand how it works and it's more complicated than simply adding water occasionally with the Ossis.

I just bought last month the best hygrometer I've seen since my Abbeon Cal and it's also from Abbeon about $140 made in Germany using a synthetic hair. Mine was spot on out of the box, our shop's one was off and we calibrated it and they both work as well as anything we have ever used. I think this is a Fischer.

Happy to help and thanks for the kind comment Michael.

Have you strung it back up yet, or are you just sighting the neck? It may come out better than you think...or not.

Before getting into pulling the inlays and grinding the board, I’d suggest stringing it up after the frets are pulled, if you’re going that route. It could be that without frets, you’d get a good amount of relief, in which case you may be able to use a fret tang barber type set up, and thin your tangs, the opposite of doing compression fretting.

I don’t use CF in my necks, except the expensive brand. And that’s only because the volute is a stress riser, so I run the CF rods out through the faceplate for strength...I think even 2 rods only adds ~10% extra stiffness or something non dramatic.

Hello Hesh...

It's great to see you back here. We need more guys like you.

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There's something doesn't make sense about this. Usually, wood shrinks in low humidity and usually the fretboard wood (which looks like ebony in the pic) will shrink more than the neck wood and the neck pulls into forward bow. Again, usually, the CF is installed close to the neutral axis and doesn't make a whole lot of difference. So what's going on? A non-wood fretboard might explain the back bow, but not the fret sprout. Is the truss rod in upside down? Was it all put together under proper humidity control with the parts at equilibrium? What are the neck and fretboard woods? Or is it just one of those unusual ones?

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I agree, a neck flattening with low humidity is a little strange.

If indeed it is dry have you tried a humidification chamber for a few days at 70% or so?

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It's not what you don't know that hurts you, it's what you do know that's wrong.

The shop RH is a constant 43% @ 20C. All wood is stored in the same space. The fretboard is Gabon Ebony, the neck shaft is ribbon Sapele. Perhaps the sapele is more susceptible to shrinkage than hondo? I’ve built 60+ instruments with sapele necks and all but this one are still perfect.

I checked it again today and it does seem to be returning to something I can fix.

M

It's very common to see Martins in Michigan winters go into back bow and so too do many other guitars when the neck and guitar dries out. Additionally the dome on an acoustic may collapse as well prior to cracking and also bring the strings in contact with the frets.

Nothing unusual about this neck's behavior at all. Back bow with dried out guitars is one of the most common things we see mostly a few months ago now that the spring rains are here.

I don't see the CF as causing the back bow, again it's one of the most common repairs we do but I do see the CF limiting the amount of usefulness of the truss rod and it's adjustment range and that's counter to the purpose of the truss rod.

Yet another reason folks to use double action truss rods. We frequently have to add relief with the rod on dried out acoustic guitars. A double action rod can save the day in these instances.

Some people plane boards we sand them with our leveling beams because we will also be using the beans to impart relief which we can't do with our method with a big-arse plane. You may have to deepen a fret slot or two in the middle of the neck and be sure to clean out the fret slots very well (Stew-Mac hook tool) so that when you refret compression is not excessive and causing your newly reshaped fret plane to go back into back bow.

We have to distill our efforts into manageable operations to know what to bill a client. This would be a refret with some added hump time milling the back bow out, deepening some slots, etc.

Which is a great environment for building, but perhaps not ideal to rehydrate a severely dried out instrument. Like Hesh's experience in Michigan, I see dry guitars regularly here in Québec with super-low winter humidity.
You say you've noted some change recently, and I expect that would continue for several weeks. You can speed things up a bit by rehydrating in a more moist environment -- I use a guitar stand in a very large garbage bag, with a couple of large, damp sponges in the bottom. It might take 2 weeks for the guitar to rehydrate even in that environment. Keep a close eye on it -- you don't want to overdo this.
I have no experience with CF neck reinforcement -- I've never been convinced of its merits -- so can't really comment on its impact on your current problem, although it sounds like it's working against the truss rod?
To follow up a bit on Hesh's comments on Oasis humidifiers. I've never heard of the OM1, but I do stock the soundhole and case versions of their Plus+ humidifier, the OH-5 and OH-14, respectively. These are higher output than their regular OH-1 and OH-6 models. The case version is especially useful, if it can fit, as the player can simply leave it in place as they remove and replace the guitar.

I'm also puzzled. I'm familiar with low action (buzzing strings) on guitars that have been subjected to low humidity. It doesn't happen as routinely in my neck of the woods, but when it does, it is always a loss of top doming.

Hesh-- I respect your experience, and I'm trying to figure out what's going on. What would explain neck back-bow as a result of low humidity? What part of the neck is shrinking more, and why?

Don't get too hung up on the question why. Necks are actually a complex structure with a lot going on: weirdly shaped; one part finished and one part not; a truss rod moving things in various directions and then the carbon bars. Introduce low humidity and stand back.

Necks are extremely complex and even more complex because of the infinite variables in grain and the very fact that wood is not an homogeneous material by any means. Everything we introduce adds possibilities too.

But this is a very common occurrence and one of the reasons why with steel string guitars that have any chance of not being perfectly cared for during their expected life double action rods and the few extra bucks to use them can literally save thousands in repair costs.

TIm OH-1 is what we have and glad to hear you like the Ossis too. I must have OM on the brain.

I would add to what Hesh said about double action rods... Make them removable too!

Even better! Great point.

I think Ed Bond may have indicated the cause of the problem. Normally woodworkers ignore the lengthwise expansion and shrinkage of wood or make vary small allowances for it because it doesn't change much. Under extremely dry conditions the length of the neck may have shrunk slightly, with the frets then acting as "compression fretting" and causing a slight back bow. Pulling some of the frets and releasing the back bow, and recutting the slots before refretting might allow the neck to regain it's proper shape.
Here is a brief article on the lengthwise shrinkage of wood:
https://www.fpl.fs.fed.us/documnts/fplt ... 4-1942.pdf
It is interesting what it says about curly wood.

UPDATE:

I followed Tim’s suggestion and rehydrated the neck using a plastic bag and a couple of damp sponges. Thankfully, the neck comes off in a minute or two. After 4-5 days there is no more fret-fang, and the neck came back to flat with a neutral truss rod. This morning I decided to string it up: It has proper neck relief, it’s back to its previous 5/64-3/64 at the 12th, and it is playing beautifully again! I took a fret rocker to it and found two frets that were about .001” high. I’m gonna let it further acclimate for week or so before making any additional adjustments.

Thanks everyone for your sage input!

Best, M

I would let it readjust to 45% or whatever it has to live in for a week or so and recheck. Previously shrunk wood can be blown back up with heavy humidity but it may not stay that way anymore.

When we force cracks closed with the sponge in the bag method we are sure to check our cracks several days later to make sure they didn't reopen and they at times do. Wait, that doesn't read as I intended...

Anyway hopefully the rehumidification holds but at times doesn't so maybe be sure before sending it back to the desert.

I got the impression Micheal was taking a sensible “allow time for acclimatisation” approach — hysteresis should generally work in his favour. What worries me more is future guitars built with this “ribbon” figure sapele. I stay away from figured wood for necks as all figure is full of interlocked grain where wood movement with moisture change is unpredictable. Longitudinal shrinkage and swelling of wood vessels is indeed minimal, but the axis of vessels in interlocked grain is not parallel to that of the neck. Ribbon figure occurs in fast-growing tropical hardwoods and is largely an environmental phenomenon in areas that experience wet and dry periods. The ribbon is full of interlocked grain — pretty obvious when you apply an edge tool. To my mind, it’s suitable for backs and sides, but not for necks where dimensional stability in service is paramount.


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+1

Michael--You say you've built dozens of guitars with sapele necks and not had a problem. How many of those had ribbon figure? Have you built other guitars with necks from the same billet?

Eric, I’ve build 4 or so from this billet and more than 60 instruments with ribbon sapele, this over the last 12 years. This is the first one to have an issue. I’ve found it to be very stable and only require the standard biannual TR adjustment if at all. Most of my guitars live between Northern California and British Columbia. This is the first time I’m aware of one of mine experiencing extremely low humidity. It’s coming back

Cheers, M

Eric, I’ve build 4 or so from this billet and more than 60 instruments with ribbon sapele, this over the last 12 years. This is the first one to have an issue. I’ve found it to be very stable and only require the standard biannual TR adjustment if at all. Most of my guitars live between Northern California and British Columbia. This is the first time I’m aware of one of mine experiencing extremely low humidity. It’s coming back

Cheers, M[/quote]

That's an enviable track record Michael. I've never built with sapele. Good to know that it's a reliable neck wood option.

Im a bit late on this subject, thought I would offer my nickels worth. With every instrument which i sell out of my shop is included an instruction sheet regarding care. 80% of the instructions are of proper care in dry conditions. Plus, when I deliver the instrument, i sit with my customer and have what I call "the talk". Ive dealt with this only once- a guitar which found its way to the dry conditions in Colorado.
Mostly I see it in old guitars brought to me for repairs. Same routine for each of these. The wet bag for a day or two or whatever is necessary, then hang in my build room at 45% for a week or so to stabilize.
Ive been dropping CF bars into my HR necks, as I've found it helps with sustain, but notably if you're not paying close attention to the necks straightness when you are epoxying the bars in, you can get into trouble when it comes to strung- up time and setup! So I definitely agree with Hesh's cautions regarding the use of the CF bars.

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On the other side of the coin, high humidity can kill too. My sister had violin when she lived in Hawaii, which came apart when the glue joints in the top and neck joint let go. It had been stored for a couple of years in a closet, so mold could have been a factor; I don't know--I never saw the damage. Her boyfriend "fixed it" with epoxy.

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