So that new Washburn I got.. Not only did it need a hilariously huge shim (almost 3mm), but the neck is all sorts of fucked.
It's a shame because it's a genuinely great sounding/playing guitar... below the 12th fret. Anything above that is chaos!
You see that? The 22nd fret is closer to the string than the 12th. The neck isn't bent like other bent necks are bent. What I mean is, it doesn't dip with a smooth gradient like on other necks with too much relief. It's perfectly straight until about the 15th-17th fret, then starts to come back up!
I've tried all sorts of shimming configurations; shimming at the neck end of the heel, shimming at the bridge end of the heel, shimming evenly across the heel... Even shimmed the nut! (there's some open-string buzz on the B and high E) but nothing has worked.
If you fret the high G-E above the 15th fret, each fret plays the same note
The only way to remedy it is to raise the action to an almost unplayable height.
Truss rod is turning but doesn't appear to be doing anything (it's a heel-end jobby). It must have had about 3 whole turns, and has barely done anything.
That actually doesn't sound that weird to me - usually it's not that pronounced, but that would be sort of par for the course for a neck with a little TOO much bow, where the bridge was set relatively low to compensate. Straighten the truss rod a hair and raise the bridge a little and see what happens.
You may have also shimmed a little TOO much neck angle into it.