Severe back bow on Modern construction neck, any way to fix it ?

docteurseb

Senior member
Messages
759
Just noticed Modern construction neck I ordered last summer, stained in December, and finally got back from the finish shop couple weeks ago has in fact developed a massive back bow even without tightening the truss rod at all.

No idea if that happened while storing it before staining, after, or while waiting for a finish at the finishing shop. It doesn't matter since it was ordered w/o the penetrating sealer and is therefore not covered under warranty (well understood when ordering that way).

Do you guys know of any technique to attempt fixing this ?

It's that bad with the straight edge flat against the fingerboard at the first fret:
dj2IW6J.jpg


You can even see the heel lifting up from the flat table...

Is it toast ? If the only answer is to use string gauge 25 then I can either use it as decorative item or dispose of it on Thursday (trash day)...
 

docteurseb

Senior member
Messages
759
On second thought it may well have happened this week-end trying to clean up the finish along the rolled fingerboard edges (it was a bit of a mess the way I received it).

Had to use a sharp blade to clean up the finish and then apply thin superglue to blend it in (and prevent lifting in the future), the end result looks great but thin superglue did manage to get underneath the fingerboard's masking tape.

When trying to remove the mess I left many tool marks on the fingerboard.
I thought steaming them out could work with a damp paper towel + soldering iron tip. However that may well have caused expansion of the ebony fingerboard between frets and caused the backbow.

If so, maybe this can be corrected by drying the fingerboard, pulling out moisture with a heat gun ? But that has its own risks when it comes to frets/glue and the poly finish.
 

ragamuffin

Senior member
Messages
1,008
I have no advice to give, but I wish you the best of luck! Looks like a beautiful neck
 

mayfly

Senior member
Messages
8,309
Cagey is the man to talk to.  He has this funky oven / clamp system together that works for extreme cases
 

triple jim

Active member
Messages
49
It seems like the steaming could be the problem, or have contributed to it.  Anything to gently dry the moisture from the steaming might help.  Just leaving it face up in the warm sun, for example.
 

Sadie-f

Senior member
Messages
427
I'd say start with a bag of rice. Use whatever is handy to form a trough, line that with plastic wrap or aluminum foil, lay down a bed of rice, and nestle the fretboard into that.

If that doesn't do the trick, you could distribute even weights along the fretboard, optionally with a curved support under the back of the neck and let pressure / time do the job?

Here's some details of what's going on over time and application of force and humidity in wood.

https://jwoodscience.springeropen.com/articles/10.1007/s10086-016-1565-4
 

Rick

Senior member
Messages
4,544
I have two methods, both involve loosening the truss rod.
Then:
1) put one end of the neck on bucket.  Put the other end of the neck on another bucket.  Make sure it's level.  Hang a 5 pound weight in the middle.  Wait a week.  If it doesn't work, add a 10 pound weight.  One week later, voila.
2)Metal bar, wood blocks, stair tread rubber and a c clamp.
At the ends of the metal bar, one that won't bend, more like a beam, put wood and a piece of rubber stair tread, with the rubber touching the neck.
In the middle put c clamp.  On the neck put wood block and rubber where the c clamp is.
Slowly apply pressure a little bit every day.  Check once a day. once almost flat, voila, you're done.

I learned the later method from Dan Erweline.  I just read it one of his books.  He probably has a youtube video on it.
 

stratamania

Senior member
Messages
9,486
Perhaps follow the advice in this video from Dan Erlewine. He covers back bowed necks in the video.

[youtube]https://youtu.be/dL6kJ6iAGpg[/youtube]
 

docteurseb

Senior member
Messages
759
stratamania said:
Perhaps follow the advice in this video from Dan Erlewine. He covers back bowed necks in the video.

[youtube]https://youtu.be/dL6kJ6iAGpg[/youtube]

Thanks. Unless mistaken the only backbow he covers is at the end on a dual action truss rod, basically showing how to adjust a dual action truss rod for back bow which isn't applicable here (it would, with a Musikraft neck).
 

stratamania

Senior member
Messages
9,486
DrSeb said:
stratamania said:
Perhaps follow the advice in this video from Dan Erlewine. He covers back bowed necks in the video.

[youtube]https://youtu.be/dL6kJ6iAGpg[/youtube]

Thanks. Unless mistaken the only backbow he covers is at the end on a dual action truss rod, basically showing how to adjust a dual action truss rod for back bow which isn't applicable here (it would, with a Musikraft neck).

The Warmoth Modern construction "double truss rod" is a "dual action truss rod" so it should be applicable I think using the heel adjust rather than the side adjust.

Edit. Some describe this truss rod construction also as dual action. But it differs construction wise from other rods sold as such.
 
C

Cowbell Fever!

Guest
I do not know. But it seems to me that it will require both dry heat and pressure to get the wood unbowed again. My idea would be to gently clamp it fingerboard down on something like a 4x4" and keep it in a small room with a space heater for a couple days. Maybe with a bag of sand at both ends.

Or something similar?
 

triple jim

Active member
Messages
49
stratamania said:
The Warmoth Modern construction "double truss rod" is a dual action truss rod so it should be applicable I think using the heel adjust rather than the side adjust.

It's a double rod that has one rod acting against a second rod instead of against the wood of the neck like most do.  It is only single acting and can't correct backbow.

Since this may have happened from the steaming of the fretboard, which could have cause it to swell, getting that moisture out may correct at least some of the problem.
 

Sadie-f

Senior member
Messages
427
rick2 said:
I have two methods, both involve loosening the truss rod.
Then:
1) put one end of the neck on bucket.  Put the other end of the neck on another bucket.  Make sure it's level.  Hang a 5 pound weight in the middle.  Wait a week.  If it doesn't work, add a 10 pound weight.  One week later, voila.
2)Metal bar, wood blocks, stair tread rubber and a c clamp.
At the ends of the metal bar, one that won't bend, more like a beam, put wood and a piece of rubber stair tread, with the rubber touching the neck.
In the middle put c clamp.  On the neck put wood block and rubber where the c clamp is.
Slowly apply pressure a little bit every day.  Check once a day. once almost flat, voila, you're done.

I learned the later method from Dan Erweline.  I just read it one of his books.  He probably has a youtube video on it.

I'm sure these both work, and while I have limited experience with bending wood, material science is my day job, so I would worry about applying load to a single point and  also of not providing a limit to the available space for bending.

Also, based on what we think was the cause (moisture applied principally to the fretboard, and also at the edges, not the whole surface, I'd think there are some pretty big bending forces being applied at the edges (so in compression), in opposition to tension forces in the middle of the fretboard. Then again, I'm an engineer somewhat given to overthinking things?

@DrSeb, if you're not materially bound by schedule (or patience), you could wait for the moisture to equilibrate, which might or might not solve the entire problem. Short of full solution, you may find in a few days or a week, you have less bow that will need correction. Otoh, if moisture hasn't equilibrated when you apply force, then as moisture leaves, you may find your corrected back bow becomes a forward bow.





 

stratamania

Senior member
Messages
9,486
Triple Jim said:
stratamania said:
The Warmoth Modern construction "double truss rod" is a dual action truss rod so it should be applicable I think using the heel adjust rather than the side adjust.

It's a double rod that has one rod acting against a second rod instead of against the wood of the neck like most do.  It is only single acting and can't correct backbow.

Since this may have happened from the steaming of the fretboard, which could have cause it to swell, getting that moisture out may correct at least some of the problem.

You are correct re the backbow I misspoke it may not be as effective as others. It is though one rod acting against a bar, if it were two rods then it would be like a dual action rod. Though some describe this as a dual-action rod in any case.

[youtube]https://www.youtube.com/watch?v=EKVWr8FRJNc[/youtube]
 

docteurseb

Senior member
Messages
759
stratamania said:
DrSeb said:
stratamania said:
Perhaps follow the advice in this video from Dan Erlewine. He covers back bowed necks in the video.

[youtube]https://youtu.be/dL6kJ6iAGpg[/youtube]

Thanks. Unless mistaken the only backbow he covers is at the end on a dual action truss rod, basically showing how to adjust a dual action truss rod for back bow which isn't applicable here (it would, with a Musikraft neck).

The Warmoth Modern construction "double truss rod" is a dual action truss rod so it should be applicable I think using the heel adjust rather than the side adjust.
Double rod for sure, but dual action ? I was hoping so too but it sure acts like a single action truss rod
 
C

Cowbell Fever!

Guest
I still say loosen rod, lay on flat surface and weight down with sand bags in a dry heat room for a week.
 

stratamania

Senior member
Messages
9,486
DrSeb said:
stratamania said:
DrSeb said:
stratamania said:
Perhaps follow the advice in this video from Dan Erlewine. He covers back bowed necks in the video.

[youtube]https://youtu.be/dL6kJ6iAGpg[/youtube]

Thanks. Unless mistaken the only backbow he covers is at the end on a dual action truss rod, basically showing how to adjust a dual action truss rod for back bow which isn't applicable here (it would, with a Musikraft neck).

The Warmoth Modern construction "double truss rod" is a dual action truss rod so it should be applicable I think using the heel adjust rather than the side adjust.
Double rod for sure, but dual action ? I was hoping so too but it sure acts like a single action truss rod

I just edited my previous post. It seems these types of truss rods are described by some as dual action versus the double rod dual action which are more closer in function in terms of action. Which alas does not help much in the end with the back bow you have in the neck.

 

docteurseb

Senior member
Messages
759
Sadie-f said:
rick2 said:
I have two methods, both involve loosening the truss rod.
Then:
1) put one end of the neck on bucket.  Put the other end of the neck on another bucket.  Make sure it's level.  Hang a 5 pound weight in the middle.  Wait a week.  If it doesn't work, add a 10 pound weight.  One week later, voila.
2)Metal bar, wood blocks, stair tread rubber and a c clamp.
At the ends of the metal bar, one that won't bend, more like a beam, put wood and a piece of rubber stair tread, with the rubber touching the neck.
In the middle put c clamp.  On the neck put wood block and rubber where the c clamp is.
Slowly apply pressure a little bit every day.  Check once a day. once almost flat, voila, you're done.

I learned the later method from Dan Erweline.  I just read it one of his books.  He probably has a youtube video on it.

I'm sure these both work, and while I have limited experience with bending wood, material science is my day job, so I would worry about applying load to a single point and  also of not providing a limit to the available space for bending.

Also, based on what we think was the cause (moisture applied principally to the fretboard, and also at the edges, not the whole surface, I'd think there are some pretty big bending forces being applied at the edges (so in compression), in opposition to tension forces in the middle of the fretboard. Then again, I'm an engineer somewhat given to overthinking things?

@DrSeb, if you're not materially bound by schedule (or patience), you could wait for the moisture to equilibrate, which might or might not solve the entire problem. Short of full solution, you may find in a few days or a week, you have less bow that will need correction. Otoh, if moisture hasn't equilibrated when you apply force, then as moisture leaves, you may find your corrected back bow becomes a forward bow.

That's the problem: I'm not the patient kind.

While it'll be an awfully expensive mistake given the neck+finish cost, I'm happy to donate it if it takes longer to fix it than ordering+finishing a new one. Even if it becomes flat again, I'n a little concerned about the integrity of the neck but worth a short at this point.

Right now I'm following the clamp approach advice: applying pressure in the middle of the neck forcing a forward bow with a clamp with the neck resting on the flat bench (with padding at the headstock and heel to prevent damaging the finish).
I agree that helping remove moisture is probably needed as well, if the root case is as suspected.
Leaving it in a hot room is not an option here.
I could heat gently with a heat gun but it would be such a short duration that I'm not certain it would get much moisture out.
I will try the rice approach, though it's not terribly easy to do while the neck is being clamped.


There is a technique called fret compression which can be used to flatten (add back bow) a fingerboard for guitars without a truss rod (or with so much forward bow the truss rod can't correct it fully). As I understand it's basically re-fretting the neck with wider tang to force expansion of the fingerboard along its length.

I think that is what happened when I tried to steam out tool marks (that wasn't very successful, by the way, compared to light sanding...); except it caused much more expansion than fret compression ever would.
 
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