Single action truss rod completely relaxed - neck still bowed forwards

Discussion in 'Hardware, Setup & Repair [BG]' started by InternetAlias, May 9, 2019.


  1. InternetAlias

    InternetAlias

    Dec 16, 2010
    Somewhere
    So, I bought a really cheap Stagg bass guitar to mod it and before I started leveling frets, I realized the neck is bowed forwards when the truss rod is in relaxed state. I took it off a guitar 7 days ago, it's still bowed.

    What should I do about it?

    1) Remove the frets and plane the fingerboard (the bow is 1-2mm at max) (this might also have a + of letting me reset the radius to my desired radius)
    2) Leave it the way it is, and level the frets in as flat of a state as I can get it by tightening the truss rod
    3) Something else?

    As for nature of the bow - it seems like a very natural, uniform bow - the neck doesn't seem to be twisted or warped, it just seems like it deformed plastically due to the truss rod stress. Guess the neck wood isn't the strongest, but I won't complain about it since I got the whole guitar for $50 to play around with.
     
    Last edited: May 9, 2019
  2. Jeff Scott

    Jeff Scott Rickenbacker guru..........

    Apr 11, 2006
    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?
     
  3. InternetAlias

    InternetAlias

    Dec 16, 2010
    Somewhere
    I didn't make something clear. The strings have been removed. The neck is also removed from the body.

    The neck is bowed FORWARDS with the truss rod in a relaxed position, when there's no body or strings

    If I leave the truss rod tightened in such a way that the fingerboard is straight (which I can do because the neck is evenly bowed), I can level the frets/fingerboard without an issue. However, if I relax it completely before leveling anything, I will change the shape of the fingerboard, such that it'll be fatter in the middle.

    So that's why I am trying to figure what's the best thing to do before I plane the fingerboard/level the frets.
     
  4. guts

    guts

    Aug 13, 2018
    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.
     
  5. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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.
     
  6. InternetAlias

    InternetAlias

    Dec 16, 2010
    Somewhere
    Ok, I get what you mean, but since the neck has a natural forward bow, wouldn't planing it flat when it's at 60% actually shift the operation range far too much? And wouldn't it cause way too much back bow at that point (without the strings' tension), that the fingerboard becomes way too thin in the middle of the neck?

    The way I see it, if I tighten it to 60%, and it then gets a backbow, the strings will pull it back quite a bit, and if I want to combat that, I might need to tighten it more. Where before I had 0-100% correction, now it's only 60-100% since the truss rod will never really need to be loosened bellow the 60% mark, since 60% is now "flat" where before it was "backbow", and strings (45-105) will put quite a strain on the neck.

    If I want to have the neck completely flat at this point (without strings' tension), I need to put the truss rod to about 30%, and it's currently sitting at about that value.

    I might have something quite backwards, so I'd be thankful if you could correct me.
     
  7. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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?
     
  8. InternetAlias

    InternetAlias

    Dec 16, 2010
    Somewhere
    Oh, that makes perfect sense, thanks! I didn't quite get that truss rod needs to be engaged, I thought it worked more "passively", but you made it clearer.

    So, do you do this with new guitars as well? Put the truss rod in, then tighten it to 60%, then level the fingerboard and put frets? Seems counter-intuitive. I am asking because I am going to make my own neck in the near future.

    Also, what do you think about adding a U aluminum channel to the truss rod, for example, if the neck is particularly narrow (say it's a 4 string bass with 15mm spacing or something). Does it help any?
     
  9. dwizum

    dwizum

    Dec 21, 2018
    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.
     
  10. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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).
     
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  11. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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?
     
    Last edited: May 10, 2019
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  12. InternetAlias

    InternetAlias

    Dec 16, 2010
    Somewhere
    So I tightened the truss rod to about 60% as you instructed (which is basically one full turn, I can do about 7.5 quarter turns so I guess this is roughly 60%) and the neck is mostly lstraight... but, tightening the rod this much revealed there's a slight warp to it. Nothing that can be fixed by planing the board, though, but I wonder if this pre-tightening will help make sure plastic deformations are less likely to happen in the future? According to what you said, this should reduce the number of ANY SORT OF DEFORMATIONS which would be super cool!
     
  13. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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.
     
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  14. InternetAlias

    InternetAlias

    Dec 16, 2010
    Somewhere
    Just to clarify, I meant to say "nothing that CAN'T be fixed by planing the board", the lump is actually quite small!

    Thank you for sharing your knowledge, this is surely going to save me quite a bit of headache in the future! I might even try to fix a friend's bass that was previously said to be untreatable. There's nothing to lose since the neck is really all sorts of messed up.
     
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