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  #1  
Old 12-02-2018, 02:51 PM
Troubled Joe Troubled Joe is offline
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Default 12 String bridge height

Hi; 1st time poster, please be gentle !

I recently picked up what appears to be a bargain 1st 12 string - a Seagull S12+ to be precise (not sure what the “+” refers to - there is no rogue 13th string concealed and the tuners appear to be perfectly serviceable base metal rather that the 18 carat gold I was hoping for but there you go) and -as far as my playing allows it sounds great.

Other than a slightly dirty and dry looking fingerboard it looked to be in good nick till I looked in more detail a the bridge. The saddle looks to have been lowered to such a degree that the high e string is (are !) almost flush with the bridge. Presumably this was to lower the action, though there still appears to be some movement in the truss rod - I was thinking of fitting a new saddle and tweaking the neck to compensate but is there any reason beyond the cosmetic to do so ?

Any advice much appreciated !

Last edited by Troubled Joe; 12-02-2018 at 02:52 PM. Reason: Auto text buggeration
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Old 12-02-2018, 06:09 PM
AZLiberty AZLiberty is offline
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Quote:
Originally Posted by Troubled Joe View Post
not sure what the “+” refers to - there is no rogue 13th string
I believe the + means it has a Gloss Top.

(at least my S6+ Cedar has a gloss top)
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Old 12-02-2018, 09:20 PM
charles Tauber charles Tauber is offline
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Short answer...

With prolonged string tension, guitars begin to "fold" in the middle: the upper bout rotates "into" the sound hole, the top begins to deform concave between the sound hole and the bridge and the top begins to deform convex between the bridge and the end of the guitar. This changes the geometry that the strings make with the original plane of the top. The change in geometry results in the strings being higher off the fingerboard.

To compensate for the rising string height, the saddle is lowered. As the changes in geometry continue, over time, with repeated lowering of the saddle, one runs out of saddle to lower. That is, the projection of the saddle, particularly on the lower-height treble strings, approaches zero. When the angle the strings break over the saddle are less than about 6 degrees, strings often buzz or lose tone.

With the added tension of 6 additional strings, 12 string guitars are more susceptible to the deformation of the guitar's geometry.

When one gets to the point that the projection of the saddle from the top of the bridge is insufficient, there are three options, depending upon the specifics of the individual instrument. First, there is slotting and ramping the bridge pin holes. Doing so moves the exit point of the strings closer to the saddle, increasing the angle the strings break over the saddle. Second, there is shaving the height of the bridge, exposing more saddle and lowering the exit point of the strings from the bridge. Third, there is a neck reset, in which the angle the neck makes with the guitar body is altered to restore a desirable string height.

The truss rod is not used to make changes to the string height: it is to alter the curvature (relief) of the neck. The curvature of the neck is unrelated to the angle the neck makes with the body: neck angle cannot be altered with a truss rod adjustment.

From your description, it appears that you got a bargain price on the instrument because it might require expensive repair work to restore a sufficient break angle of the strings over the saddle while maintaining a desirable string playing height.

12-string guitars are notorious for the exact issue you are describing and is something that one should examine carefully prior to purchase, new or used, as it is a potentially expensive repair.
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Old 12-04-2018, 09:55 AM
Troubled Joe Troubled Joe is offline
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Thanks for your advice; I took it to a local tech who didn't believe a neck reset was necessary but recommended shaving the saddle and ramping the pin holes - so not a dead loss !
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Old 12-04-2018, 12:06 PM
ship of fools ship of fools is offline
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I doubt that the guitar is folding in on itself the saddle may have been lowered just because he wanted to lower the action for his play style without any other info as to the height of the strings at the 12th fret or pictures and it was a good thing to take to a pro but I am not sure shaving the saddle or did you mean bridge cause if you shave the saddle well won't it be lowered even more, is the best way to go its a lazy mans fix so if he hasn't started just have a new saddle made and the fool around till you find the right spot.
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Old 12-04-2018, 01:14 PM
MC5C MC5C is offline
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If you take the position that guitars are changeable things that need periodic fettling, as do I, then the idea that a highly stressed guitar like a 12 string might need bridge work, even a new bridge, and neck work like a reset over time is a reasonable idea. "Shaving" a bridge means reducing the height of the bridge itself by up to around 1/8th of an inch so that the saddle stands prouder above the bridge with the strings at the same height over the top itself. That does little more than change the string break angle and offer the opportunity to lower the action a bit, and is quite a common tweak. Eventually the tweaks aren't enough and a reset is required, and possibly even a new bridge to replace the now-too-low original, but keeping an older, inexpensive guitar going for a few more years is often a good choice.
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Old 12-04-2018, 02:46 PM
Troubled Joe Troubled Joe is offline
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Yes, oops, shaving the bridge, not the saddle- that would make precisely no sense !
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12 string, action, bridge, saddle, seagull

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