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Neck backbow problem


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Okay, I'm building a 5-string bass out of mahogany (neck & body). I installed 2 carbon fiber rods and one of those trussrods-in-a-square-box. Fingerboard is a pre-slotted, pre-radiused PauFerro board from LMII. Everything seemed straight before I glued the fingerboard on.

Now that its glued on, when I put a straight edge on the top of the fingerboard I can clearly see a gap (backbow) of 1/8" (3mm)!!

What should I do to fix this??

Someone recommended to me to install the neck on the body and string it to see if the string pressure would bring the bow back. Would this work?

What about sanding? Do I have to sand the board until the backbow is out?

3mm sounds like a lot of wood gone from the fingerboard, not to count the fact that the part where the fingerboard touches the neck on the sides will have a radius line.

Any suggestions anyone??

I should mention that the neck is not shaped yet in the back and not fretted yet.

Here's a bunch of pictures to show exactly what I did with it.

This is a picture of the neck as it is right now.

Neck_as_is_2.jpg

On this picture you can see where the carbon rods and the truss rod finish in the neck. Carbon rods, somewhere between the 1rst fret and nut. Trussrod between 2nd and 1rst fret. The stuff i'm putting in is silicone to stop the rods from rattling and moving in the channel.

Neck_glue.jpg

This is the end of the neck where the rod will be ajusted. Again, the white spots are silicone, that stuff dries transparant.

Neck_pocket.jpg

And if you guys are curious, just for the hell of it here's the body where this neck will end up.

neck_body.jpg

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Since this is my first instrument I guess i'm allowed stupid mistakes..... :D

I didn't check with a straight edge before I glued. The fingerboard seemed straight and the mahogany neck was straight because we passed it in the planer before we bandsawed it. But that was in december, so it was about two months in that shape before I glued the neck on. You think the neck might have twisted in that time?

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the reason I'm asking is becuase I had a similar thing. I had a curly maple neck blank that was pretty weak, but I decided to give it a try anyway. The fingerboard (braz rosewood) had a backbow, but I decided to give it a shot anyway.

After I glued it on, the whole neck developed a backbow.

However, since you have a trussrod AND CF rods, I'm clueless why your neck developed a backbow.

Is the trussrod a one-way or two way?

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Well, you know what I think of Vox Humana, but a good neck really doesn't need a two way adjustable rod.

I'm still clueless what happened to your neck. what if you lay down the neck on a flat surface with the fingerboard down? There just has to be a leveling problem as I don't believe a neck with CF rods caqn develop such a horrible backbow.

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I've got my money on the mahogany developing a back twist. We checked it originally when it was planed, it really was straight then. If I put a straight egde on the side of the neck along the lines where the fretboard meets the neck wood, you can see the curvature. so it really is a backbow of some sorts. i'm just pissed that after installing a big ass trussrod and two carbon rods I still get that!

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Oh jeez.... not exactly what I want to hear.

I guess i'll try to level the fretboard for now, If worse comes to worse I guess i'll have to redo a new neck.

What sucks though, is that I now have to buy a radiused sanding block and fretsaw in case I have to reslot if I sand down to low. Which pretty much means I bought a pre-radiused and pre-slotted fingerboard for nothing.

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I never made a bass neck out of mahogany and I think it's not strong enough for a bass neck, but I'm not 100% sure about that.

If you'd have to make a new neck, you can remove the fretboard following the tutorial on the PG web site. It's a time consuming job, but it can be done (I did it once).

What radius does the FB have?

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12 inches.

Have you ever bought wood at the Arnhem Fijn hout handel? Is it affordable for neck wood? Reason I ask is I tried to buy a piece of wood for a bass neck in a wood yard here in the Hague and for a piece of maple just a little bit bigger than a bass neck (1" X 5" X 30") or (25mm X 125mm X 750mm) I was asked for 55€ Ouch!

Needless to say, I didn't buy it, and I bought enough mahogany in a lumber yard back home in Montreal to build 2 necks and a body for about 50€ during christmas vacation, which I brought back here.

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Yes, I bought at AF. The maple was pretty good... I had four strat neck blanks made and it cost me about $32 for the wood.

I got some very nice birdseye maple coming in this week for a J bass that I'm building. I think I can make two necks out of it, so maybe I'll sell the rest.

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yes they will naturally bow a little because they are not locked in and so they twist side to side

my advice is to remove the fingerboard,replane it flat.rerout the proper depth for all the rods,and glue them in....be sure the routs are tight because they work best with a good fit.....

also planing wood on only one side(such as with a neck)and then leaving it sitting without a fingerboard glued on can cause the wood to move from moisture,or at least that is what i have heard...so glue it back together soon

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Well, here goes, I removed the fretboard. It took only an hour and i'm pretty happy to see that the fretboard and the neck are both in great condition. Man, was I affraid of ripping/breaking one of those in pieces.

Funny thing is that the fretboard had now got an upwards bow and the neck's backwards bow is MUCH smaller than before. Anyway, I'll sand this thing flat and glue the fretboard (and carbon rods!) back on tomorrow.

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