Official Luthiers Forum!

I am currently involved in a discussion about the best way to correct a backbow in a neck that has only a single action truss rod. My view is that heating the neck and fingerboard and clamping it in a jig to impart relief and letting it cool in the new configuration is preferred.
The opposition insists that planing the fingerboard and refretting is the best way.
My feeling is that this is horribly invasive, especially to vintage instruments, weakens the structure by removing material, threatens inlays and results in a fingerboard of uneven thickness along its length.
I would plane or sand only to correct unevenness in an otherwise straight board before a refret.

What is your take on this?

I would try the heat clamping first, then try planing if the first job doesn't work.

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"Act your age, not your shoe size" - Prince

Nothing to loose by heat treating but our belief here at Ann Arbor Guitars is that heat treating when it does work, and it often does not...., may not last very long either. More specifically it may not be a long term fix. At times there are good reasons why a neck will do this reasons that we can't counter without getting invasive. Unseasoned wood comes to mind too.

One thing that is missing for me in this situation is what the instrument is, specifically. I'm asking because economics comes into play often with examples being that resetting necks on inexpensive instruments with dowelled neck joints is not economically feesable usually for all concerned.

Craig let us know that the instrument is please so both of us here can draw from experience specific to that instrument?

Many thanks my friend.

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Ann Arbor Guitars

It is a Gretsch of some sort. Not sure of the model, import or domestic, new or old/vintage.
I am awaiting more info from the original inquirer. Will ost as soon as I have more to tell
Thanks all
Craig

I have to agree with Hesh on this one. It's been my experience with the heat press that it is a temporary fix at best.The twist or bow may not be as bad as the initial one after a while but a degree of the original problem has returned about 70% of the time for me.

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Blue Ring Acoustics
blueringacoustics.ca

Craig my friend I've asked Dave Collins to weigh in here too but until he does one of the issues with heat treating necks is this: We are basically slipping a glue joint when we heat treat.

Depending on the glue used getting glue to release does not alway mean that it will reactivate and/or reactivate with the same degree of strength that the original glue joint had. As such even heat treating can be considered invasive in so much as the glue joint will never be the same again. This can lead to problems down the road, fret board coming loose, etc.

Dave should be along shortly though and he can shed a lot more light on this than I can.

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Ann Arbor Guitars

I approach heat treating with great caution, and there are a great many variables with individual cases which can determine its appropriateness and reliability.

There are two main principles at play in heat treating - bending the wood (as when steam bending a side), and slipping the fingerboard glue joint. I'll start with my thoughts on the glue joint.

First, it's a bad thing to do. Glues that are applied moist are generally evaporative curing. When applied in liquid state they form their essential bonds as the solvent (usually water) evaporates. Even through hide glue is considered both thermal and evaporative curing, the thermal stage really only brings it to tack, and the final bonding occurs through evaporation of the solvent. Once this initial bonding is complete, even though the glue may soften enough with heat to let the joint creep, it will never reset in the same way once heated and strained. It will be permanently weakened. Same applies for epoxies, which can involve both thermal and chemical curing, when softened with heat, strained, and allowed to reset, they will not reform the same types of bonds and strength will be permanently compromised.

Then there's heat bending of the wood. Pronged exposure to high heat is also clearly shown to affect a permanent loss of stiffness in wood, though with low heat typically used in this application I'm not sure how much of an effect this really has. The bigger risk here I feel is peripheral, and again related to the glue joint. If a neck settles in to a warped state over time, it could be due to stress over time (a neck in irrecoverable upbow after sitting for years with heavy strings and the truss rod entirely loose), or being built from compression or tension wood, which often is not apparent in kiln dried planks, but may later develop distortions over time. Now perhaps you could bend the wood to correct this with a permanent set, but to do so you generally have to apply such heat and force that the glue joint will inevitably be affected as well. So we're back to that problem.

And as much as removing material through board re-leveling may be obviously invasive, compromising the integrity of a structurally critical glue joint could be argued as even more invasive, even if less immediately apparent.

All that said, we do heat treat. We just do it very selectively, and will only use this method in cases where we have good confidence that the results will be reliable at least for a good length of time.

If a neck is in minor backbow, with a loose truss rod or none at all, and without any significant twists that need correction, we will sometimes use heat treating. In these cases we will use low heat (<130°F) under moderate stress, for a long duration (4-8h), and allow to cool overnight before removing the press. In these cases we can get fairly predictable results, though sometimes the operation needs to be repeated (I prefer small steps approaching the goal over going too far and having to try to bring it back). The long term stiffness may be slightly affected, but in years of doing this I've not seen any cases where the neck was weakened enough to pull further in to upbow over time, and string tension tends to keep it from recovering back to its original backbow.

For warped or twisted necks I will not attempt this. I have in the past, and although I've seen short term success and a few last some time, the rate of failure is too high, and too many necks will return at least to some degree back toward their original state. Same with upbow cases. Here any minor decrease in stiffness will allow string tension greater opportunity to pull it back to relief. Those are typically cases for compression refrets. And finally, I don't consider cases of extreme backbow to be suitable candidates. If it moved that far back before, it will likely do so again even if you can correct it in the short term.

So minor backbow cases, yes. Just use low heat. I own two personal guitars I have done this to, and both have remained stable in the 10-15 years since. You just have to use good discretion as to where this approach has the best chance of being a reliable solution.

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Eschew obfuscation, espouse elucidation.

This has always been my experience as well. The wood has for whatever reason deformed to accommodate the stresses imposed on it by the strings. Even if you do get it straight it will start to readjust itself when the stress is applied again.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

The reality also is that some manufactures produce junk..... and error on the side of being cheap and using unseasoned wood over going to the trouble to do it right.

We all know that when we build we in a perfect world want to only build with wood that we have had under our control for some years that has been allowed to season.

Consider this: If we were a large guitar f*ctory one of the functions would be to anticipate annual sales say five year out and order and stock enough wood so that five years from now we have well seasoned wood to build with.

This is not an easy thing to do and even more difficult when considering the nature of many guitar producers who live and operate on the edge of oblivion much of the time. When a guitar company has to make the choice of paying employees or buying lots of wood that will not be flipped for say five years you can see where I am going with this.... I suspect that post great recession instruments are suspect for unseasoned wood as a result.

Back to Craig's issue with the Gretch.

One possibility if too much back bow is the issue is that if there is minimal fret wear in the first couple of frets you could do this:

1) adjust the rod for the least back bow possible.

2) support the neck in the middle region where the back bow is most severe.

3) if and only if the degree of back bow and the height of the frets is such that using a long beam you can still level the frets and if you have to take the middle ones down to say .020" of height the board will remain in back bow but the fret plane won't and will be level.

4) recrown and perhaps even encourage 10's or greater so as to exploit the most string pull possible to get you your relief.

An alternative is always a refret too but leveling out the hump in the board gets invasive to the inlays that you mentioned and inlays on these can be pretty thin at times. You could remove them, the inlays and then reinstall them after taking the hump out of the board. A lot of effort but if the client's budget is such that protecting the investment in the instrument warrants this it might be the way to go.

What's interesting about this one is that as Luthiers we often are not just in the position of fixing an instrument - often it's the case that we have to essentially finish the proper building of the instrument because the f*ctory didn't.... Now you know why I spell f*ctory as I do..

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Ann Arbor Guitars

I want to thank you all for taking the time to share your knowledge and years of experience with me so that I now have a better understanding of the "whats and whys" of the process. My experience has been with the minor backbows and so far have seen the repairs hold. For forward bows I czn definitely understand Brian's point about the necks wanting to return to their bowed condition under the stress of string tension.
Thank you especially to Hesh and David Collins for their in depth explanations. I hope that you don't object to me sharing. This is why I love this forum, for the opportunity to communicate and learn from some of the finest builders and repair people around.
Thanks to Lance for hosting this invaluable resource to our community.

My Best to All,
Craig

No problem Craig - we believe that the reason that we are here is to share and help when we can. If you hadn't noticed I love this stuff and live and breath it nearly every waking moment... I even come home at the end of the day after fixing guitars and pick up my own guitars and get reminded why I became a Luthier. I'm compensating for being a lousy player....

Take care

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Ann Arbor Guitars

You could consider a sort of "anti-compression" refret. I have never tried it but this always comes to mind when I hear about back-bow. Has anyone done this? The idea would be to use fretwire with a tang that is just slightly narrower than the slot, on the frets in the middle of the fretboard. Be sure to glue the frets in, but in theory the string tension should lock them in place. Then level the frets under string tension. There would be trial and error about how many frets to use the narrow tang wire, but you could get it close then get it just right with a fret level under string tension. Blues Creek Guitars sells wire with different tang widths, and you can get a fret leveler for use with strings on on Ebay (sorry forgot the name).

On neck straightening with heat - it's a good idea not to get it too hot or you can bake the inlays to a powdery crisp. I learned that the hard way!