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Bow in the neck?

Discussion in 'Hardware, Setup & Repair [BG]' started by Phoebus125, Sep 6, 2008.


  1. Phoebus125

    Phoebus125

    Aug 24, 2008
    Connecticut
    Just asking - forgive me if it seems like a stupid question, as I am not quite as involved in the world of the bass guitar as I am with the trumpet - but is the neck on a bass supposed to have a slight bow in it? For the longest time my Fender bass had a slight inward curve on the neck, and it played alright...since I kept it in my moderately humid basement all summer, the neck is now completely straight and it buzzes and clacks like crazy. So I was wondering if a bass is supposed to have a light curve in the neck.

    And for no particular reason except my own curiosity, how exactly does the truss rod work? Like, what is happening mechanically when you turn it?

    -Phoebus
     
  2. XylemBassGuitar

    XylemBassGuitar Supporting Member Commercial User

    Aug 14, 2008
    Durango, CO
    Owner and Operator, Xylem Handmade Basses and Guitars
    Hi Phoebus,

    Yes, a majority of basses and guitars operate the best with a slight amount of "upbow" or "relief" in the neck. Reason being that strings vibrate in an elliptical pattern. So, a slight bow in the neck will follow the contour of the vibrating string whereas a flat neck would interfere with the elliptical contour, causing fret buzz.

    Single action truss rods (ones that only bend the neck in one direction--away from the strings) are usually installed deep in the neck, (at least below the first half of the neck's thickness) with a large washer at the adjustment end and a "anchor nut" at the fixed end. When you tighten the adjustment nut, it pulls the washer and anchor nuts closer together, compressing the back of the neck.

    Because the rod is installed deep in the neck, there is more wood above the rod to resist the compression than there is below the rod. Thus, only the back of the neck is compressed, causing the neck to "backbow", counteracting the pull of the strings.

    Double action truss rods usually don't work by compressing the neck wood. Instead, they usually consist of a rod that is bent so that its two halves are next to each other (like a very skinny "u".)

    Then, an adjustment nut is affixed to the top ends and, when tightened, causes the rod to move against itself, causing a bend. Turning the nut in one direction causes a backbow, turning it in the other causes an upbow. A double-action truss rod works by actually bending itself.

    By the way, you could probably fix up the buzz on your bass by loosening your truss rod slightly (make sure the strings are tuned up to pitch when you loosen the rod). Start by only loosening it about 1/16 - 1/8 of a turn, then check the relief to see if you need to loosen it more.

    If you have more questions about adjusting the rod on your bass, let me know.
     
  3. Phoebus125

    Phoebus125

    Aug 24, 2008
    Connecticut
    Thank you very much! Your advice helped me solve the problem.

    -Phoebus
     
  4. XylemBassGuitar

    XylemBassGuitar Supporting Member Commercial User

    Aug 14, 2008
    Durango, CO
    Owner and Operator, Xylem Handmade Basses and Guitars
    Glad to help out!
     

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