This week we took in a 1960′s Fender P-Bass for a refret that had a severely warped neck. The neck simply would not straighten out, no matter what we did with the truss rod – even with the truss rod completely loose, the neck had a severe back bow.
Here’s the fretboard against a straight edge – yikes!:
Sometimes we can true the fingerboard with sanding and radius beams, but this bass has such a thin rosewood fingerboard that it just wouldn’t work – we’d blow right through it. In this instance, we’ve decided to do a heat press.
Here’s the heat press process in a nutshell: the fingerboard is heated, which softens the glue joint between the board and the neck. This allows the wood of the neck and the fingerboard to move in relation to one another as we bend the neck towards it’s proper orientation. After the neck cools, the glue re-hardens and the neck holds it’s new, straighter, shape. We first place the neck in our heating caul, like so:
The neck is placed against a flat aluminum bar, which is heated with a heating blanket, which in turn is sandwiched by another aluminum bar, and then the whole thing is clamped tight with the rounded clamps you see in the above picture. We use tongue depressors as shims if needed. The neck is then slowly heated, slipping the glue joint, and then we wait several hours as the neck cools ans the glue dries. Then we check the neck with a precision straightedge, and if necessary repeat the process. This one took two tries, but it’s better to be conservative in the beginning to see how the neck reacts.
This neck straightened out nicely, and is now ready for the next step: installing the frets.