Heat treating a neck?

[Keith Guitars]

Heat treating can work very effectively, and as Hapa suggests, the primary mechanism at work is to reset the glue joint between the neck and the fingerboard.

That glue joint is subject to considerable shear force, and most common woodworking glues are pretty weak in shear, with hide glue and epoxies being the exceptions.

When that glue joint 'creeps' over time, the neck will settle into a forward bow. By heating and softening the glue, you can reset the glue joint and straighten the neck. I've done this many times quite successfully. Older Martin guitars are particularly good candidates for this since they have no truss rods, and were often strung with heavier strings over the years.

Another common cause of this is the wood itself creeping - maple is actually worse than many woods in its tendency to deform under a static load. The fibers in the back of the neck will stretch, and this will result in a permanent forward bow. This can be offset by 'slipping' the glue joint as described above, which in this case can be a permanent fix, since the neck wood has stretched about as much as it can, and often won't go further.

As for the one-piece neck - there is still a glue-joint present, whether it's on the fingerboard (compression surface) or on the back of the neck (tension surface). Slipping the glue joint on the 'skunk-stripe' could be just as effective as doing so on the fingerboard, since it would just as directly address the fiber-stretching issue.

Leaving your guitar in a hot car is a really good way to end up with a warped neck. It's sometimes hard to believe how easily you can straighten a neck (and/or remove the truss rod) with relatively low amounts of heat. The last neck I straightened like this (about 2 weeks ago) was done with a 100w lightbulb. Worked like a charm! I've removed fingerboards with that same lightbulb.

Resin glues like Titebond, etc. get seriously weakened over about 150 degrees F. It's not hard to hit those temperatures in a closed car, especially in a black case in direct sun. If the guitar is up to pitch in those conditions, it's its own worst enemy.

Cheers!
Martin

 

[OldogNewTrick]

Thank you for providing a sensible explanation. Makes total sense.

But works only on thermoplastic adhesives, like PVAc and variants. Wouldn't work so well with MUF, UF or PUR adhesives.

So the creep permitted by the adhesive ist at the same time the luthier's back door for repairs.

 

[joeyl]

so, I have a neck that has a huge forward bow at rest. Can I clamp it in a slight back bow, and stick it in the hot garage for a few days, in hope that the slow heating up during the day will reset the glue line between the board and the neck?

 

[202dy]

so, I have a neck that has a huge forward bow at rest. Can I clamp it in a slight back bow, and stick it in the hot garage for a few days, in hope that the slow heating up during the day will reset the glue line between the board and the neck?

If the garage can achieve a temperature of approximately 175F degrees it will work. That is assuming that the glue used to bond the neck and fingerboard is white woodworking (polyvinyl resin) glue. If the factory used yellow (aliphatic resin) glue, figure 225F. Probably be a good idea to leave the car in the driveway.

Heat is not cumulative. In other words, leaving something in a garage at 115F for three days is not the same as heating it to 175F for an hour. You would be better served to use some small halogen lights. Martin has had good luck with a 100w light bulb. Some folks use an infrared heat (par) lamp. Repair shops use a silicon heat blanket. When using these items it is important to stay with the project. Do not answer the phone. Do not go out for a smoke. It is easy to scorch a finish and the fingerboard or melt plastic inlays or bindings. The difference between a soft glue joint and damaging the guitar is a very short period of time.

 

[joeyl]

If the garage can achieve a temperature of approximately 175F degrees it will work. That is assuming that the glue used to bond the neck and fingerboard is white woodworking (polyvinyl resin) glue. If the factory used yellow (aliphatic resin) glue, figure 225F. Probably be a good idea to leave the car in the driveway.

Heat is not cumulative. In other words, leaving something in a garage at 115F for three days is not the same as heating it to 175F for an hour. You would be better served to use some small halogen lights. Martin has had good luck with a 100w light bulb. Some folks use an infrared heat (par) lamp. Repair shops use a silicon heat blanket. When using these items it is important to stay with the project. Do not answer the phone. Do not go out for a smoke. It is easy to scorch a finish and the fingerboard or melt plastic inlays or bindings. The difference between a soft glue joint and damaging the guitar is a very short period of time.

Thanks! I will keep that in mind, it is a fairly new Fender P neck fretless that I bought here in the classifieds, and it looks like it will need help. I may stick it in the car outside then, with the outside temps reaching 100F, it should be nice and toasty inside the car. I would use the lamps but I am concerned that like you said, it is too focused and will burn parts of the neck if not careful

 

[202dy]

Thanks! I will keep that in mind, it is a fairly new Fender P neck fretless that I bought here in the classifieds, and it looks like it will need help. I may stick it in the car outside then, with the outside temps reaching 100F, it should be nice and toasty inside the car. I would use the lamps but I am concerned that like you said, it is too focused and will burn parts of the neck if not careful

Focused heat is preferred! With lamps, or better yet, heat blankets, you are in control. There is no way to control the activity in the automobile. Using the automobile means that the entire instrument will be brought up to the temp needed to soften the glue joint. That includes the joints in a laminated neck, the headstock, and the body. The recovery time-the time it takes to bring the automobile back up to temp after checking the instrument-in an automobile is considerable. That means constant monitoring for an even longer period of time than using focused heat. And running the risk of compromising every glue joint in the guitar.

Not recommended.

 

[joeyl]

Focused heat is preferred! With lamps, or better yet, heat blankets, you are in control. There is no way to control the activity in the automobile. Using the automobile means that the entire instrument will be brought up to the temp needed to soften the glue joint. That includes the joints in a laminated neck, the headstock, and the body. The recovery time-the time it takes to bring the automobile back up to temp after checking the instrument-in an automobile is considerable. That means constant monitoring for an even longer period of time than using focused heat. And running the risk of compromising every glue joint in the guitar.

Not recommended.

point taken. Thanks!

 

[bassie12]

Using information gleaned from this thread and a few other sources, I managed to take a back bow out of a very stiff ‘59 Precision Slab board neck using a heat lamp and specific tension placed on the neck. It’s been stable under a good set of fiatwounds for a few weeks now. Will report any changes...

 

[jeffreylee]

I did this on an older Teisco guitar and it worked. It got the guitar pretty cheap and it was unplayable so I decided it was worth the risk. I WAS a bit careless and scorched the binding but the neck has stayed straight and playable 5 years later.

 

[Samatza]

Both my Tune basses are in for a neck reset but in opposite directions. One needs a slight forward bow the other a slight backbow. It's not a lot really and after 33 years on the road between all sorts of climates and both have pencil thin necks you can get a little bit of movement in the glue joint.

My luthier tells me it's no big deal, has done many neck resets and they all seem to work fine. If they go another 33 years they will probably outlast me.

 

[fhm555]

I build basses for a living. I have done repairs using a heat treating method and it works. Most simply don't do it correctly, mainly leaving the heat on the neck for too long and then unclamping too early. Or in instances where there is not a truss rod or a cheap truss rod or a rod that has been forcibly bent out of effectiveness nothing can really straiten out the neck. Also keeping in mind an unstable neck is almost always forever an unstable neck. If it ever got so far out of whack that it even needed a heat treatment, why is the player even considering relying on it?

I am reading above and I think yall have the wrong idea about what heat treating is all about. Its not at all about bending the wood back into shape its resetting the glue.
The glue is heated and softened usually with a heating element and flat metal block with dots/blocks covered to prevent burning/ scorching (fixing an upbow) and with the truss rod neutral. When heated it should be clamped to a back bow (slightly...by experience) meaning the body of the guitar needs to be set in a jig. unless one has a string tension simulation jig with a fitting for that type of neck. the fb clamped to a flat heating block with remain parallel in radius to the back bowed neck. like clamping a finger board to a backbowed neck from the start like classical guitar builders used to do before truss rods existed but after the fact.

Doing this can cause many other problems with the neck after the fact as well. If you are applying enough heat to loosen glue on the neck the same applies to Frets, they can easily come loose. Dots and blocks can easily be damaged or binding, ivoroid binding can go into full combustion. pearloid same thing anything cellulose based really. Its not a strait ahead repair and results are not always what you want. Most guys won't do it because of all the other stuff that can happen not that it doesn't work.

I had a really slim neck twist playing in a really damp outdoor situation. I took it my buddy the tech and he fixed it. He said essentially ^this^, said he heated it up until the (rosewood) slab on top was loose, them clamped it down with no twist and let it sit overnight. That was in 92 or 93 and it’s been fine since then.

 

[Turnaround]

Leaving your guitar in a hot car is a really good way to end up with a warped neck.

Quite right. And if the heat buildup in a car is enough to cause the warp, the same amount of heat is all that's necessary to take it out.

 

[202dy]

Quite right. And if the heat buildup in a car is enough to cause the warp, the same amount of heat is all that's necessary to take it out.

Never subject your guitar to an environment in which you would not leave a human or a pet.

The same amount of heat won't fix them.

 

[vaesto]

I've heat-treated one-piece neck and it woked for me. So it is not all about softening and resetting the fingerboard glue. Though, only two month has passed, and I can't yet say it is "rock solid" solution.

 

[M.R. Ogle]

I have a Fender HM Bass IV acquired in a trade because of the dreaded "tongue rise" which made it unplayable past fret 13. I knew the "usual" cure for this was a removal of the upper frets and to plane down that area, but I wasn't wanting to go that drastic. The "WarpedNeck.com" guys said they could fix that, so for less than $100 bucks... I figured, "what the heck..."
It worked. Two years and it's still flat. I'd consider at least TRYING that method first on any subsequent necks. It might work for your particular problem neck.