Advice on a small warp in neck

[ShatnersBassoon]

I was going to post this in my current build thread but thought it might be bad manners to clutter up the thread with deviations

So the piece of wenge that I want to use has been roughly cut to shape and the truss rod route has been done. Only issue is that it bows up slightly (maybe 0.25 mm) in the centre of the blank. It’s super dry by the way and has been left in a drawer for a few years. 

I seem to have lots of problems sanding wenge, so is it feasible at all to just carry on with the neck build and rely on the tension of the strings to straighten it? It’s going to be quite a thin neck when it’s complete so just running through options. Cheers everyone!

Actually...just thought about fret levelling issues. Problematic!

[Bizman62]

If you're using a dual action truss rod there should be no issue.

Also, when gluing the fretboard you can bend the neck flat. The fretboard should keep the neck then straight. And no, I didn't invent this, it's a thing I've seen used several times to fix a bowed neck without a truss rod in Rosa String Works' videos.

[Bizman62]

Adding to that, if you're going to use the fretboard trick, I'd install the frets first to avoid backwards bending while trying to straighten the neck.

[ShatnersBassoon]

Thanks Bizman! I will crack on.

[ShatnersBassoon]

On 12/5/2022 at 3:49 PM, Bizman62 said:

If you're using a dual action truss rod there should be no issue.

Also, when gluing the fretboard you can bend the neck flat. The fretboard should keep the neck then straight. And no, I didn't invent this, it's a thing I've seen used several times to fix a bowed neck without a truss rod in Rosa String Works' videos.

Don’t want to take up too much time, but do you know what terms to search for with regards to the fretboard trick? Or maybe explain it briefly? I’ve searched high and low for it and can’t find it

Thanks so much for the help! 

[Bizman62]

I've seen that done on RosaString Works videos, currently I'm about at #455 so it most likely has popped up somewhere between #350 and that, in a couple of videos where they repaired old acoustics without a truss rod.

In all simplicity it's about clamping the center of your neck to create an underbow. Small blocks at the ends to raise them up and a clamp in the middle:

Obviously you'd need another bunch of clamps to glue the fretboard to the neck but for clarity I just drew "the One Clamp to rule them all". For keeping the fretboard aligned you can also glue part of it in place beforehand. I'd do that at the heel end as that's the most stable and static part of the neck. Glue something like one third or a quarter of the fretboard down and let it dry for an hour or so the glue is still somewhat soft but won't break loose. Then raise the other end of the fretboard and apply glue to the rest. A spatula might be good in the tightest spot.

You can most likely exaggerate a tad with the underbow during gluing as the wenge will try to retain its backbow and it's thicker than the fretboard.

[ShatnersBassoon]

Thanks again Bizman! Really appreciate it.

[ShatnersBassoon]

One last thing Bizman Probably obvious, but I’m guessing the fretboard trick is done with the truss rod in there? Not forced in afterwards? Guessing it wouldn’t put to much strain on the rod? Or would I turn it slowly as I’m clamping? 

[Bizman62]

As I may have mentioned the trick was used to straighten necks that didn't have a truss rod so we're in a bit grey area here...

But yes, inserting the truss rod afterwards would be clumsy at best and a nightmare at worst.

Starting with a similar bow to the neck and slowly turning while clamping sounds like a plan. Good thinking!