Single action truss rod completely relaxed - neck still bowed forwards

If you have forward bow you need to tighten the truss rod to flatten the neck out.

Or did you really mean to say - back bow?

 

It sounds like you gotta plane the fingerboard, if you want to try to fix it, but I wouldn't count on it solving the problem for the long term.

It's a bad sign that the neck is warped like that. It's possible that it could warp even more down the line and you'd have to plane the fingerboard again.

It's a bad piece of wood. Not suitable for a neck. Poorly selected.

 

We've had a few long detailed threads on this subject before: How should you adjust the truss rod before leveling the frets and/or trimming the fingerboard to flat?

Quick answer: Think of the truss rod as having a range from 0% (loose) to 100% (As tight as you dare). Tighten it to about 60%. Wherever the neck ends up in curvature, leave the truss rod at 60% and trim the fingerboard to flat. Refret it, and level the frets, still keeping it at 60%. This is with the neck off, no strings.

What this does is ensure that you have a good range of operation of the truss rod, when it's all strung up and under load. String it up, with it still at 60%, and it should pull to a small amount of relief, approximately right. From there, you can tighten or loosen the truss rod a small amount to dial it right where you want it.

 

Yes, you are missing several things:

The tighter the truss rod is, the more stable the neck becomes. The tension of the truss rod is a brace, countering the tension of the strings. That balance of tensions in the steel helps prevent the neck wood from moving and bending. A neck that's strung up and set at the right relief, with the truss rod at 60%, will be more stable. You won't need to adjust it as much when the humidity changes. So, you don't need a wide range of adjustment. Your seasonal adjustments will be between 55% and 65%, staying well within the mechanical capabilities of the truss rod.

If you cut the fingerboard so that, under string tension and the right relief, the truss rod is close to loose, then you are putting more load on the wood. It's going to change more with the weather because it's not supported as well. You'll need more adjustment range, and the neck may even bend beyond what the truss rod can handle.

If you start out by adjusting the truss rod to make the neck as flat as you can, that certainly makes the job of flattening the fingerboard easier. And the fingerboard will look more even visually. But the truss rod may end up loaded too lightly or too heavily, so it can't do its job. And the neck is unstable or unadjustable.

What I'm saying is to first adjust the truss rod to the right loading (around 60%). Then, whatever curve the neck ends up at, make the neck flat by cutting it flat. Even if that means that the fingerboard ends up thinner in the center. That's what you need to do to make sure that the truss rod will work correctly.

Do you understand the difference?

 

You seem to be hung up on getting the neck to some standard position when it's off the bass, not strung, and not under any of the forces it'll be when in use. While it's good to have a reference point when the neck is not under tension, what really matters is what the truss rod and neck relief are like when in use. Your desired reference of setting the neck flat with the rod slack is somewhat arbitrary (it's not derived from some desired end state), Bruce's method will get you a neck with the truss rod about where you want it when it's actually in use.

Having the rod engaged and actively part of the structure definitely helps in stability from a humidity perspective, to the extent that if I have an instrument that ends up with the right amount of relief with the rod totally slack, I'll usually turn the rod until the slack is taken up and it's just coming under tension (but not yet significantly changing the curve of the neck) in order to keep the rod engaged.

 

Yes, I sure do. That's an important part of building necks that will be stable for decades. I cut the radiused surface of my fingerboards, already glued on the necks, with a router in a special fixture that holds the neck between two rails. During the setup of the neck in the fixture, I "pre-tension" the truss rod to about 60% or so.

I keep the truss tight during the installation and leveling of the frets too. During final setup, I may need to slightly tighten or loosen it from that point to get the relief just right. But it's only a small adjustment, if any. Historically, my bass necks have been very stable out in the field over the years. Only a few of my customers have ever needed to adjust the truss rods over the years. And it's generally only once, as the bass first gets used to their climate. Of course there are many other design and construction details that go into my necks to make them stable, but pre-tensioning the truss rod is an important one.

This is another one of those little details that goes into an expensive bass. The big manufacturers don't do it because they are trying to shave every penny out of the labor cost. Too much extra work (although it really isn't).

 

If you want to get into the subject of reinforcing necks and stiffness vs stability, etc., check out this thread first. And there are others. In the Luthier' Corner, we talk a lot about how to design and build necks.

Neck reinforcement rods vs truss rod

Check out this thread too:

Aluminum reinforcement rods? Maybe?

 

That's exactly the right thing to do. Bring the truss rod up to the right load, and inspect the neck to see where it is. Look for any warpage or lumps in the fingerboard. Keeping the truss rod tight, trim the fingerboard flat, removing the warpage or lumps. You are cutting them away, permanently. Now, whenever the neck goes up to load, it will be flat. That's the whole point. Make the neck flat, while under load in playing condition.