How To Straighten A Guitar Neck With An Adjustable Truss Rod

Discussion in 'Guitars in General' started by HaywireGuitars, Feb 25, 2012.

  1. HaywireGuitars

    HaywireGuitars Member

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    The neck of your guitar is adjustable

    (Angled Headstock style of adjustable truss rod)

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    Angled Headstock style of adjustable truss rodSource: Haywire Custom Guitars Inc.


    Most guitar players are familiar with a truss rod. They also have an idea that it is an adjuster of sorts. That's the beginning of understanding how to adjust a neck with it.

    In most cases, the neck of a guitar is adjustable. Although the wood is generally hard, dry and stiff it will still bend with string pressure and humidity or lack thereof. In our shop we have to deal with that issue on a daily basis. Inside the neck is a routed channel between the finger board and the neck shaft where a truss rod is placed to compensate for movement on the forward axis of the neck to add stability. The rod is steel and is adjustable. It runs the length of the guitar neck with an opening at one end allowing for adjustments.

    The truss rod both strengthens the neck and facilitates an adjustment called "relief" in the neck. A bowed or humped neck can be reversed with skillful manipulation by the adjuster-you. All guitar necks are subject to great stress. This is sometimes the result of seasonal change, Other times when a neck could take on a slight bow or hump are from string changes with gauges higher than normally used. A guitar player will usually know a little about how to make some adjustments on his guitar. Some things however may contribute to a misaligned neck.

    Several of the "usual problems" seen are heavier gauge strings which increases the forward pressure, removing all of the strings at once and leaving guitars in a hot car. These actions will cause immediate negative pull and the will revert naturally back to where it started. However, if it does, there is a solution if you follow the procedure below for proper repositioning of a bowed neck. In our Custom shop this is the procedure we use.

    First, loosen all the strings but you will not have to remove them. Push the loose strings to one side to gain access to neck adjuster. If you are in an extreme hurry then forget loosening the strings. I can be reported accurately from personal experience that in the shop after doing literally hundreds of necks-the proper and best way to "get it right" is to loosen the strings. Why? There is such a thing as "regression" when it comes to materials that bend-like wood. When the wood and truss rod come together on the inside of the neck sometimes they "stick" and will not come loose until the string tension is relieved. Think of it as tuning a guitar. Using the same reasoning with why you tune down past the note FIRST before you tune back up to get the right pitch and have the note stay where you want it. The same applies to neck adjustment. You need to de-tune the neck before properly re-setting it and tuning it back up and straight. This is the right way-although everyone has their own ideas on what is best. However, why re-invent the wheel when you can learn by the experiences of others who do it every day for a living.

    Remove cover, so neck adjuster is exposed. It's either an Allen screw or a hex nut. Look down the neck from the top where the tuners are located towards the bridge (similar to sighting a down the barrel of a gun) to see how much of a bow or hump the neck has in it.

    It is recommended to use a Notched Straightedge to see how far out of alignment the neck really is. The notches are on both side of the tool. One side has cutouts for a 24-3/4" scale neck and the other is for the most common 25-1/2" scale. They are there so frets can be avoided when the tool comes in contact with the fret board. The frets fit neatly in the cut out and the straight edge will show any problems when it lies straight on the fret board.

    At this point, if it is discovered that the neck is out of adjustment, it's time to go to work. Insert the Allen key or hex wrench in the Allen slot or on the adjustment nut and turn very gently in small increments at a time. Checking the neck as you proceed with each nut turn is required. Once the neck is straight keep adjusting a bit more to compensate for the tension the stings will add once they are re-tuned to pitch. Turn right or clockwise for " BOW " alternately left or counter clockwise for a HUMP. Take special care as not to tighten the nut too much because it could result in a broken truss rod, stripped threads and a much larger monetary outlay than originally intended.

    This should fix the problem! If there seems to be an inordinate amount of "string buzz" that you find impossible to live with bring it in to your guitar tech for further inspection. If the neck has a "twist" it can void the neck straightening process you have just used and will need attention from a Luthier.

    On some "Vintage Guitars" the adjustment is the same but in a different location. It is made at the end of the fingerboard called the Heel or Butt end.



    Haywire Custom Guitars "Violator"

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    Source: Haywire Custom Guitars Inc.
     
    Last edited: Feb 25, 2012
  2. GCDEF

    GCDEF Supporting Member

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    I don't see the need in loosening the strings. I never do. It's quicker and easier to get it right if you leave them in tune.
     
  3. Mrmarshallhead

    Mrmarshallhead Member

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    It's essential to leave them up to pitch in my opinion. After all I am setting the neck relief to the most suitable level for playing the guitar, not leaving it laying around with loose strings. I also adjust it with the guitar in playing position.
     
  4. Voodoo Blues

    Voodoo Blues Member

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    If you're trying to straighten a neck with the strings tuned to pitch you're also fighting the tension of the strings when you're tightening the truss rod. Loosening the strings takes some of the tension off the neck and therefore truss rod.

    Another couple of tips, if it feels a little hard to turn try backing it off 1/8 turn first to loosen it up a bit.

    Only go in 1/4 turn adjustments at a time. Restring and remeasure.
     
  5. GCDEF

    GCDEF Supporting Member

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    I wouldn't call it much of a fight. It's not hard to adjust the rod with the strings tuned to pitch, and it's much quicker than loosening, adjusting, tightening, checking, loosening, adjusting, tightening, checking...
     
  6. B Money

    B Money Member

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    yeah but the string tension is part of the equation. You can't properly relief a neck without it.
     
  7. stormin1155

    stormin1155 Member

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    I am also of the opinion that loosing the strings is not necessary. My primary purpose for responding though is to clarify what the truss rod should NOT be used for.

    As you stated, it adjusts the bow of neck. It is NOT for general adjustment of action (string height), although will have some effect. The primary points to adjust action are the nut and bridge/saddles. I mention this because it isn't uncommon that people think the truss rod is a magic button and start cranking on it without knowing what they are doing.

    If you want to adjust string height, you will want to first check the relief and adjust according to Haywire's instructions. Once you have the bow (relief) set, check your action at the nut end. At the first fret you should be able to slide a medium gauge pick between the string(s) and fret and the string will snugly hold it there. If it doesn't hold, action at the nut end of the neck is too high, and the nut slots need to be deepened. If you are getting a lot of buzzing with open strings, they may be too deep already. Before actually doing any work on the nut, check action at the other end of the neck, and get it roughly where you want it.

    Next you check string height at the other end of the neck. At the 12th fret your strings should be about 1/8" from the fret. I say about because some people like lower action, some like it higher. Action may be slightly higher on the bass side strings because they require more space to vibrate. I set action on my guitars at about 4/64" (1/8") on the 6th string and graduate to about 3/64" for the first string. To go any lower than that, your frets need to be VERY level, with no low or high spots.

    On guitars with individually adjustable saddles, you want to adjust height for each one. For TOM type bridges, the adjustment is only on either end.
     
    Last edited: Feb 25, 2012
  8. jtindle

    jtindle Member

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    Your diagram shows that tightening the nut for "bow" and loosening the nut for "hump". I thought if you had bow you would tighten the truss rod nut to straighten the neck. Am I all backwards?
     
  9. RCM78

    RCM78 Member

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    You and the diagram are both correct. You're just interpreting it wrong.

    If your neck has too much relief (bow) tightening the truss rod will straighten it out...
     
  10. RussB

    RussB low rent hobbyist Silver Supporting Member

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    I like to perform some "truss rod maintenance" whenever I re-string a guitar for the first time. With the strings off, I remove the truss rod nut, and apply a small dab of grease (or never-seize compound) to the threads. This will stop the nut & rod from sticking, and make adjustments easier and smoother for decades.
     

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