help! - neck/fretboard leveling question (before fretting)

[hittitewarrior]

Been awhile since I posted here.  I'm so very slow at builds.  I've been building a pair of guitars at the same time and trying some new (to me) features... the most relevant to this post is the use of carbon fiber beams in the neck.  These were installed on either side of the truss rod slot and affixed with CA.  I clamped the neck blank to my tablesaw top to ensure it was flat when i put CA in to hold the carbon fiber.  At this point, I noted no issues.  Great.  I routed down the headstock thickness (tele style guitars).  Used the bandsaw and cut out the shape of the neck and then used a router template to clean it up to the shape I wanted for headstock and neck.  I then clamped my radiused and slotted fingerboard to the neck.  Using a pattern bit, cleaned up the edges of the fingerboard to match the shape of the neck blank.  I had previously checked the radiused fingerboard for straightness along the length (was very close).

I was surprised when I double checked for straightness once the glue up was complete.  For some reason, the neck seems to have a bow in it.  measuring flatness at fingerboard shows an upbow, and measuring flatness on the back of the neck shows it is the whole neck that has upbowed (not a sanding issue I had made).   I haven't adjusted the truss rod, and i'm surprised the two carbon fiber rods did not combat any environmental changes.  Wood was dry.  Any thoughts??

What I really was hoping for some guidance on is what to do next.  I was going to fret.  I think I should fix this first?

Do I 

1) Adjust the truss rod to make it straight?

2) Sand the fretboard flat since it is currently in an untensioned (truss rod neutral) state?

3) Something else I haven't thought of?

Any thoughts or opinions would be greatly appreciated!

Thank you!!

 

[Workingman]

Two things, measurements of how much of an up-bow would be helpful.  If the carbon fiber rods are two stiff, the string may not pull the neck into enough bow for suficiant relief.  In that case of the bow is fairly small it may be a good thing.  The second is that in my experience, carbon fiber rods are installed with epoxy which holds it in place.  CA glue may have left them too loose to stop the bowing.

[Bizman62]

The first thing I'd do is to double check that the truss rod is loose, then recheck the straightness. A sanity check if you will...

Another check worth doing before applying any tools is to check if you can easily straighten the neck with the truss rod. If half a turn is enough at this stage then another half should suffice to resist the string tension.

If I see right there's some release in the neck as it now sits. An obvious culprit is that the notched fretboard doesn't resist bowing either way. I wouldn't blame using CA instead of epoxy, though, unless a) there's lots of longitudinal play in the carbon fibre slots and b) the glue doesn't hold but instead allows the rods slide in their slots. Snugly fitted rods should stiffen the neck even without gluing, logically thinking, although the glue does add to the stiffness. 

A forward bow is better in my logic at this stage as putting the frets in will add material to the slots thus bending the neck backwards. After fretting you may end up with a dead straight neck which then will get a natural release bow when stringed.

Again, my logic may fail on me here.

 

[hittitewarrior]

@Workingman Thanks for the quick response.  Upbow on the worst of the two is about .025".   

Good to know for future on epoxy.... I am kicking myself right now.

 

[hittitewarrior]

@Bizman62  Thank you for the additional thoughts!  I follow your logic.

Attached are some additional pics.  The slots were pretty tightly fitted.  The carbon fiber is taller than it is wide which is how it was installed for stiffness.  The slots were a little longer, but I went down the length of the rods and wicked CA on both sides of the rod with extra at the ends where the slot was longer than the rod.

 

[Bizman62]

Continuing the logical pondering, the slots should be a hair "too" long to allow the strings pull a bit of release on the neck. Same goes for the truss rod.

I truly believe that there's going to be no issue that can't be fixed by a minor turn of the truss rod. Just bang the frets on!

[hittitewarrior]

any other ideas or thoughts from others?  Appreciate the input so far!

[Workingman]

My bad in that I didn't notice the fret board is already slotted.  I am with Bizman62, a little up-bow will probably be countered with the compression from installing the frets.  Your rods look pretty tight so I doubt them slipping is a problem. 

[curtisa]

10 hours ago, hittitewarrior said:

any other ideas or thoughts from others?  Appreciate the input so far!

Finish the remainder of the neck construction steps (headstock, headstock transition, carve, fretting etc) and then make a decision. There's every possibility it will move some more once you start performing further operations to it, so any corrections you make to it now could just come unstuck as you start making further changes to the neck blank, and you'll have to deal with it again. If you've used a dual action truss rod and you need to correct a minor up/down bow prior to levelling, just use the truss rod to offset it. After all, the primary reason the truss rod is there is to control the degree of relief in the neck.

What are the dimensions of the carbon rods you installed?

[hittitewarrior]

2 hours ago, curtisa said:

Finish the remainder of the neck construction steps (headstock, headstock transition, carve, fretting etc) and then make a decision. There's every possibility it will move some more once you start performing further operations to it, so any corrections you make to it now could just come unstuck as you start making further changes to the neck blank, and you'll have to deal with it again. If you've used a dual action truss rod and you need to correct a minor up/down bow prior to levelling, just use the truss rod to offset it. After all, the primary reason the truss rod is there is to control the degree of relief in the neck.

What are the dimensions of the carbon rods you installed?

Carbon rods are .125” x .325”.  

I think I’ve seen it done in a couple different orders of operation, but I was planning on fretting, then headstock transition and carve.  Any reason to carve first?

Thanks for the advice!

[curtisa]

1 hour ago, hittitewarrior said:

Any reason to carve first?

I didn't mean to imply that those items be in a specific order; more highlighting that any potential movement of the neck as a result of material being removed from the blank, frets being inserted etc should be the last thing you address before attempting to level the frets.

Trying to get the neck to 'sit straight' this early on in its construction may be counter-productive if all that happens is that the neck moves again before you get to the fret levelling stage. If you re-sand the fretboard now so that it's flat, you'll end up with a fretboard that is (marginally) thinner at the ends than in the middle. If you start cutting/carving/sanding/shaping the rest of the neck and it moves again, your flattened fretboard could end up non-flat again (maybe lifting at the ends again? maybe bending back the other way? maybe twisting in an odd way?), and you'll have to go back and correct it somehow.

It's possible that the neck blank won't move any more from this point onwards, in which case doing nothing now except making the neck as you would normally will be perfectly acceptable, and all you need to do is tweak the truss rod to get the neck flat again prior to levelling. But trying to force it to appear flat and discovering it changes further down the track will just have you chasing your tail.

[Bizman62]

First, thanks @curtisa for pointing out that the neck is still uncarved. As said, the neck can be built in several orders all of which have their pros and cons. I'll try to explain:

• Leaving the neck unshaped until fretted like you did: -Gives a solid base to hammer or press the frets in but if there's any tensions inside the wood they will be released only after you've carved the neck.
• Cutting the neck to thickness: -Releases some tensions and the offcut can be used to support the neck when fretting
• Roughly shaping the neck before fretting: -Releases most tensions so you can fix a twisted neck before fretting. Supporting the neck when fretting requires some sort of a caul.
• Properly shaping the neck before fretting: -Even more potential tensions are released. One has to be extra cautious to prevent dents and nicks. A supporting caul is required for fretting.

In all methods the fret wire will change the proportions of the fretboard as it fills the slots. Cutting the frets after gluing the fretboard in adds yet another variable to all the four ways described above. The difference is minor, but it exists: An uncut fretboard is obviously stiffer than a preslotted one. Cutting the slots after glueing the fretboard on can release tensions caused by glueing and clamping two stiff boards to each other differently to glueing a flexible board on a solid one. Further, hammering the frets in will create tensions but will they counteract the released ones is another question.

All methods are acceptable and widely used. The only thing to worry about no matter which way you build your necks is warping or twisting. Bowing can in most cases be fixed with a turn of the truss rod.

[hittitewarrior]

Thank you all for the feedback and information.  This was really helpful.

And thank you @Bizman62 for the pros/cons list for order of operation.  

I will proceed as planned and pray for no warping/twisting!  

More to come!