Warped fingerboard

[Renee Labordus]

I received a new ebony slotted fingerboard yesterday. It was slightly bowed in the middle.
Not sure exactly how much of a bow, but certainly visible by eye. I am able to slide a plastic card through the gap in the middle with the ends down on a flat desk top.
Should I expect this as acceptable, and/or workable. Or do I need exchange?

[John Link]

Exchange it. You are not getting what you paid for.

In any case, the fingerboard should be dead flat on the bottom, and the neck dead flat on top. Any contouring for relief, etc. is done on the top of the fingerboard.

[ken cierp]

If you can get the supplier to exchange it that would be good -- but in reality the FB is going to take on a little bow as you install the frets -- I have never had one that did not. I don't view this as a problem since I do like (want) to see a slight bow of the extension that will compress against the sound-board. This also leads for the tendency of the neck to tilt back away from the sound-board again a good thing to prevent a reverse neck bow which is especially problematic. Now a twist is a different issue and can cause all sorts of problems.

[Tim Benware]

I received a new ebony slotted fingerboard yesterday. It was slightly bowed in the middle.
Not sure exactly how much of a bow, but certainly visible by eye. I am able to slide a plastic card through the gap in the middle with the ends down on a flat desk top.
Should I expect this as acceptable, and/or workable. Or do I need exchange?

Desk tops are often not flat. If you have a table saw with cast iron top that would give you a more accurate idea. Also, once you fret that board it will bow as well so its going to move no matter what you do. I worry more about length wise twisting, the truss rod will take care of bowing as long as the board is flat on the bottom and not twisted. If that all makes sense to you.

Edit: we must have been typing at the same time Ken:)

[Renee Labordus]

Thanks gentlemen.

@Ken…no it is a twist.

So I understand the concept you describe. Are you saying that the fingerboard ends will curve downward after installing the frets? Assuming a dead flat fingerboard to begin with. So if the ends of the ,fingerboard ends slightly curves upward, would it reasonable to assume that in my case it would end up flat? And on another note, can I install the frets before glueing the fingerboard down? ( I am almost afraid to ask)

[ken cierp]

Yes I'd say the board will straighten out

Here's my fretting procedure, I always install frets before attaching the FB to the neck.

http://www.kennethmichaelguitars.com/fret.html

I should note that when I construct classical guitars I do taper the FB -- a bit thicker at the nut end than at the sound hole end, this builds in some "required" string relief/clearance.

[Renee Labordus]

And do you taper the bottom or the top of the fingerboard?
My guess is the top. Going to be fun without damaging the slots. And then the depth of the slots at the tapered section must also be adjusted to account for the taper. Correct?