Neck Geometry 101 (with graphic)

Discussion in 'Hardware, Setup & Repair [BG]' started by Hambone, Aug 4, 2001.

  1. There seems to be a lot of mystery concerning how a neck should be setup using a truss rod or by shimming. The illustration shows the three typical setups that most of us will encounter with our necks.


    A. This is how the perfect setup would look. The neck itself is straight and the strings are set at an even distance from the frets along the entire length of the neck.

    B. This is a condition that is corrected using the truss rod. Note that the neck isn't straight and the strings are further from the frets near the middle but closer at both ends of the neck. You want to adjust in small increments until you get your neck looking like example A. The reverse of this condition is where the neck bows backwards and this too is corrected with the truss rod. Don't confuse a setup like this for the one described in example C.

    C. This is condition is only corrected by shimming the neck. Notice that the neck is straight but the strings gradually move away from the frets as they go towards the nut. Shimming alters the angle of the neck in relation to the body. You should never confuse this condition with the one shown in example B. Shimming is done by placing a thin spacer under the heel of the neck between the neck bolts and the bridge. This acts like a fulcrum and pitches the neck back to level the strings.

    I hope this helps with some of the confusion concerning the different ways necks need adjusting. If you aren't VERY confident in your knowledge of how to correct these conditions, don't attempt it! Damage can occur that will cost you more than if you were to take your instrument to a qualified technician.
  2. pkr2


    Apr 28, 2000
    coastal N.C.
    VERY good post, Hambone. A picture truly is worth a thousand words.

    I have tried and tried to put into words what you have very graphically illustrated. It always ends up sounding more complicated than it really is.

  3. Thanx Pkr2, I had to laugh at your post cuz I think I've tried to post this explanation about 3 times and have never done it satisfactorily. :rolleyes:
  4. BigJH


    Jan 20, 2001
    Cincinnati, Ohio
    WOW, Thanks Hambone. I just got finished correcting my neck. It was C that you described. So I un-screwed my neck and adjusted it. It feels great! My hands thank you and I thank you.
  5. jasonbraatz


    Oct 18, 2000
    Oakland, CA
    what if you have C on a neck through bass?

  6. Suburban


    Jan 15, 2001
    lower mid Sweden
    1: take off the bridge and route a recess for it. IOW, lower the bridge.

    2: remove the fingerboard from the neck, and plane it to a correct neck angle. Oh, there may be a problem with the truss rod scratching your planer:oops:

    3: cut the neck off, route a neck joint in the remainder, buy a new neck and srew it in - in the right angle.

    I bet a fortune there are other alternatives to choose from.
    OTOH, it is a negative neck angle is very seldom seen on a neck-thru. It is glued in with a positive angle, and it will not change, as the string tension and possible abuse will act on the entire nut-to-bridge.
    Bolt-ons have a deformable joint in that area.
  7. hyperlitem

    hyperlitem Guest

    Jul 25, 2001
    Indianapolis, IN
    ive heard from many many luthiers and guitar teachers that your not really supposed to have a completely straight neck on a bass. the only time you have a straight neck is on a fretless. Your suposed to have a little bit of bend, just a little bit.
  8. I always thought that the neck needed just a little bit of bend upward. maybe im stupid, but does anyone have a guitar that the strings are the same distance to the fretboard from the nut, all the way down? if thats the case, mine is ****ed up. when i first bought my jazz, the neck was strait, i mean strait. i had to raise the action too high to avoid open string rattle. after a 1/4 turn to the truss rod, i got just a little bend, lowered the strings and it seems perfect. did i do anything wrong? help me out.
  9. jasonbraatz


    Oct 18, 2000
    Oakland, CA
    :eek: :eek: :eek:

    .:gets down on my knees and prays i never have to do that!!!:.

  10. BigJH


    Jan 20, 2001
    Cincinnati, Ohio
    If you perfer a slight curve which way does it go? Because now my bass is like diagram A. So should I adjust it or not? I like the way it plays now, though.
  11. Gentlemen, don't think too hard about this!

    The illustrations are just that - simple illustrations depicting the differences in necks needing truss-rod adjustment and those needing a shim adjustment. Example A will appear to be straight to the naked eye when sighted along it's length. And I'm here to tell you that if it's perfectly straight and your action is where you want it and the bass plays well, then that's where the neck should be! If a small amount of curve is required to make the bass play correctly, then that's where the neck should be! There is nothing inherently magic about a small amount of bend in the neck, but don't assume that it HAS to be there to have a good setup. But I can also say that having a small amount of bow (positive - towards the strings) can and will mask problems with individual fret heights.

    Please remember that sometimes the difference between a perfect setup and a really crappy one is measured in 1/10,000th of an inch!
  12. =^..^=


    Jan 25, 2001
    Stuck on a rock !
    Top post - thanks Hambone :)
  13. BigJH


    Jan 20, 2001
    Cincinnati, Ohio
    Ok then it's settled the neck stays the way it is. Excellent Post Hambone. Keep up the good work!