Fretboard Glueup

[JME]

Hi all,

 

Having issues with gluing on a pre-radiused fretboard.

It’s an American cherry neck with a QS maple fretboard and traditional single-action rod. We’re using Titebond 1 and are jigging up the neck to produce a slight forward bow, to compensate for the Titebond’s water saturation during the fretboard glue-up process. Also, the fretboard is prefinished prior to slotting/glue-up and is absolutely flat.

 

Anyhow, the fretboard goes on fine, is allowed to dry over night, then removed from the jig and it looks great - just a slight forward bow after allowing to rest for several days. Next, we bump in the frets and do a fret level, then allow it to rest again. Well, after a month or so, the neck changes from a slight forward bow into a slight back-bow… We’ve done two necks this way and both ended up with back-bow, even though they still had a slight forward-bow right after fretting. 24.5 scale length with 9’s doesn’t create enough pull to correct the back-bow.

 

Q’s:

1. Would pressing in the frets BEFORE fretboard glue-up produce different results?

2. Or should we mill relief into the neck itself – to mimic forward-bow? We could do that, but would rather not because we use a jig to mill the neck/back contour. I could, however, easily add relief to the fretboard. Anyone do that?

3. Or should we pre-saturate the neck/fretboard surfaces with Titebond and allow them to dry, then re-sand flat prior to gluing on the fretboard – to reduce water absorption?

4. Or would switching to waterproof Ritchlite eliminate the back-bow issue?

 

Notes:

1. Would rather keep the traditional rod, because we already have the construction method down and prefer the single rod over double-action.

2. Would rather use Titebond, to allow fretboard removal if ever necessary.

3. Would rather radius the fretboard prior to glue-up because we use special jigs to produce compound radiused boards – no radius blocks used.

4. The issue we have with using epoxy is that it’s like adding a plastic sheet in-between the neck/fretboard, and is permanent.

 

If anyone knows how to consistently eliminate back-bow, please share.

 

Thanks in advance.

[Bizman62]

First, I'm no expert. I've built four necks and watched a few dozen being built during the last four years. There's been pre-slotted, pre-radiused and plain fretboards and necks of various woods and laminates and both single and dual action truss rods. Plus I've watched several hundreds of guitar building videos from several higher end builders. And all of them have been made using Titebond.

To me your procedure of creating a forward-bow seems over-complicated. I've never heard anyone even mentioning it. Our tutor, Master Luthier Veijo Rautia has told us that the fretboard is so thin that it really doesn't have much effect to the overall stiffness.

A couple of things that could explain your issues come into my mind, though.

Hammering the frets in before gluing the fretboard to the neck will create a strong back-bow to the board. The slotted fretboard is very flexible and doesn't provide much resistance to force the fret tang studs to sink to the wood.

One potential issue may be your fret slots. If they're very tight the tangs will add to the length on the upper side, causing a back-bow. I'm talking about single thousands of an inch here.

The above will accumulate if the wood used for the fretboard has a tendency of swelling length vise in moist conditions especially if the wood hasn't been thoroughly dried and tempered and/or if the building environment is much drier than the storage.

The truss rod itself may also cause such problems. If the steel is "too" stiff it may have enough strength to try to straighten itself even without tightening the nut. Another factor of that ilk is the radius of the truss rod channel. If the ends are very close to the fretboard and the center as close as possible to the palm side of the neck the force is stronger than in a milder curve.

Again, this was just some logical pondering, not stone carved wisdom.

[Crusader]

I agree with Bizman although I think if it were any of those factors it would be a problem from the start. I think the Cherry is drying out and shrinking

[ADFinlayson]

You're doing a lot of worrying about nothing IMO - I've glued many fretboards with titebond and never had issues with water in the glue causing any bowing. Bowing, if at all is normally caused from hammering in frets. 

If you're really worried, get yourself a dual action truss rod and you don't need to worry about introducing a bow. The biggest concern I would have about glueing a pre radiused and slotted board is that it's going on straight and that even pressure can be applied over the radius. 

[Bizman62]

Further thoughts about single action truss rods:

If they're too "springy" i.e. if they tend to straighten no matter how long you keep them bent, they're most likely unsuitable as they'd be acting somewhat similarly to carbon fibre stiffening rods. In a straight channel that would be less of an issue but in a radiused channel such a rod would act as it were tightened. A wider radius in the channel might help a little but calculating the right amount of "hump" for a certain spring tension can be too tricky.

If you make the rods yourself, the steel should be soft enough to stay in a bent form but hard enough not to stretch when the nut is tightened. Our tutor recommended welding sticks but I can't remember if there was anything specific about them other than the flexibility.