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Thread: Tune o matic or wraparoud question

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    Tune o matic or wraparoud question

    Hello,
    i'm wondering why those bridge are allways put angled and not strictly perpendicular to the axis of the guitar... I've made several guitars and when i adjust the intonation with a tuner, the saddles position is almost the same (same length of strings) for all the strings. Why the strings should not have the same length?
    Thanks

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    Quote Originally Posted by tepsamps View Post
    Hello,
    i'm wondering why those bridge are allways put angled and not strictly perpendicular to the axis of the guitar... I've made several guitars and when i adjust the intonation with a tuner, the saddles position is almost the same (same length of strings) for all the strings. Why the strings should not have the same length?
    Thanks
    The bridge angle for best intonation depends on string gauge and action.
    The reason for the different vibrating lengths is the following:

    Depressing a string to fret an note raises string tension and thus pitch. Means that all strings would sound sharp if fretted exactly at the middle of the vibrating length. To compensate for this the length between the 12th ftret and the bridge saddle is increased by varying degree.
    As the relative pitch/frequency raise increases with string stiffness, heavier gauge/core strings need more compensation (added length) than thinner ones. This results in the typical slanted pattern.

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    Last edited by Helmholtz; 10-15-2019 at 01:18 PM.
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    OK but i have only slithly this slanted pattern after tuning and not 3 strings by 3 strings, i use a electronic tuner and my hear is ok.
    Next bridge is a wraparound with only 2 little screws to tune it, and i don't want to fail. First attempt, i put it at the exact position and it was too sharp,and thus unplayable, i had to put a more tunable bridge, that's why i'm asking.
    Thanks

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    Why the strings should not have the same length?
    I tried to answer this question above. As said, the necessary slanting depends on string gauge and action. Low action and thin strings don't need much slanting. Traditionally guitar setups and bridge placements were intended for heavy strings.
    There is a number of adjustable wraparounds available.

    First attempt, i put it at the exact position and it was too sharp
    Not clear what you mean with "exact position" but as explained above, strings will sound sharp if you place the bridge exactly at 2x scale length.


    Which guitar type and wraparound are you speaking of? Please explain your project and post pictures.

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    i have to place this one and i don't want to fail drilling the big holes in the body. It's a PRS like body and it's true that i consider 2x the length to the 12th fret. And last time i had more than 5 mm error, and i could not adjust so much. And what kind of angle? How many degrees?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Take a look here for calculations to give a better insight into the actual values involved;

    https://www.liutaiomottola.com/formu...mpensation.htm

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    Quote Originally Posted by Mick Bailey View Post
    Take a look here for calculations to give a better insight into the actual values involved;

    https://www.liutaiomottola.com/formu...mpensation.htm
    Yeah, very helpfull ! Thanks

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    A quick look at the calculator (excellent resource, even for the non-luthier!) shows a 'default' compensation of about 1/4" at the sixth string, which correlates strongly with the error found:

    And last time i had more than 5 mm error, and i could not adjust so much.
    It's nice when theory and practice agree.

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    The other reason that strings don't intonate precisely at 2X scale length is that they don't articulate (bend) exactly at the node (nut and saddle edges) because the wire has stiffness (stiffness is a consequence of the tensile strength needed to keep strings from breaking at pitch). The thicker the string -the further away from the node is the actual articulation point. You can move that articulation point closer to the nut and saddle by "setting" the string, forcing it to bend at the nut and saddle with a firm press of your thumb nail right where the string exits the slot. This is standard procedure when changing strings. The quality of the string has something to do here as well. The better the steel alloy used the less stiff the string is for a given strength and the less extra distance needed between the nut and saddle for correct intonation.

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    The other reason that strings don't intonate precisely at 2X scale length
    Why other reason?

    The influence of string stiffness has already been adressed in post #2.

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    From a practical perspective when I've invested a lot of time and materials into a one-off build and want to be certain that I don't make a mistake I use a dummy setup just to locate everything. This consists of a board with a couple of spare tuners fitted at one end and long enough to accommodate the scale length + bridge/tailpiece. I don't bother cutting a nut - just a piece of plastic or metal at the correct height to represent the nut position. I fit a flat piece of spare fret wire at the 12th position and then mark out and drill where I've calculated the bridge to locate, making the holes an easy fit so that everything is easy to remove. Once it's strung up to pitch the intonation can be checked and any adjustments are easy to make by plugging and re-drilling as needed.

    It sounds more involved than it actually takes and it really does pay off compared with mis-drilling a body.

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