How does the double expanding truss rod in this style work?
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Cagey
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Are you sure it has a dual-action truss rod? Because if it doesn't, you could wreck the thing trying this... just sayin'... word to the wise, and all that.
A dual-action truss rod will exert pressure forward or backward, depending on where it's at and the direction you turn it. When you reach the point where the neck reaches equilibrium, the rod will feel loose. Just slightly past that, it will tighten up again, and start exerting force in the opposite direction.
The thing to do is to have a known straightedge and some feeler gauges available so you can make small adjustments and see what kind of influence you're having over the neck's planar dimension. If you're turning the nut counter-clockwise but the bow is getting worse, you're past the centerpoint, and vice-versa. You shouldn't have to move more than a quarter turn or so to find out, and you shouldn't have to force anything, although there is going to be some resistance if the neck is under any tension. It's tedious, but it's not gonna eat your life. Just be patient.
Once you know which side of the adjustment you're on, you can get where you want to be fairly easily. Let the thing set for a while, measure again, and if you're still good, string 'er up. It'll teach 'er a lesson <grin>
Let that go for a couple days, and check it again. Adjust as necessary. Small adjustments.
A dual-action truss rod will exert pressure forward or backward, depending on where it's at and the direction you turn it. When you reach the point where the neck reaches equilibrium, the rod will feel loose. Just slightly past that, it will tighten up again, and start exerting force in the opposite direction.
The thing to do is to have a known straightedge and some feeler gauges available so you can make small adjustments and see what kind of influence you're having over the neck's planar dimension. If you're turning the nut counter-clockwise but the bow is getting worse, you're past the centerpoint, and vice-versa. You shouldn't have to move more than a quarter turn or so to find out, and you shouldn't have to force anything, although there is going to be some resistance if the neck is under any tension. It's tedious, but it's not gonna eat your life. Just be patient.
Once you know which side of the adjustment you're on, you can get where you want to be fairly easily. Let the thing set for a while, measure again, and if you're still good, string 'er up. It'll teach 'er a lesson <grin>
Let that go for a couple days, and check it again. Adjust as necessary. Small adjustments.
Cagey
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Incidentally, I just noticed that the neck you've shown in the picture above is a "Vintage Modern", which does not have a dual-action truss rod. If that's what you have and the rod is loose and you still aren't getting the relief you need, the neck has a permanent bow to it. That can sometimes be repaired, but it's not a trivial task. You'll need some regulated heat and steam and a way to exert some pressure against the bow to push it past the point you want it at.
Cagey
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I've found with strings in 9s or 10s sets that unless you're a really violent player, you don't need any more than about .008" relief unless your frets need work, and that's pushing it. I typically set necks up flat and playable, then add a bit of relief for good measure to keep things clear-sounding. (Truly flat necks never really sound right acoustically, so you know you're losing something electrically). You may just need some setup attention.
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