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Acoustic Bridge Placement

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My uncle gave me this old Harmony "Sovereign" acoustic that the bridge had torn off of. Before gluing it back on I measured from the nut to the 12th fret and found it measured 12 1/2", meaning a 25" scale. So I measured from the nut to the bridge and noticed that where it was mounted before it tore off was too far back. The saddle wouldn't have been at 25". So me, thinking I'm SO smart, I mounted it so the middle D/G strings were at 25". The saddle angles back from the high E to the low E like acoustics do. After the glue dried I stuck a low E string in there and checked the intonation at the 12th fret, by ear and it's is obviously off. The bridge has to go back, probably where it originally was.

So what is the catch here? Is there a certain formula for bridge placement on acoustics? Because I measured a 25 1/2" scale electric and the D/G strings hit right about 25 1/2" from the nut :D

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The thicker the string, the more compensation it needs. Placing bridges 'on' the scale length works OK for electrics, because the bridges are adjustable. On acoustics...not s'much. You generally, ballpark figure, want the leading edge of the saddle, in the middle of the saddle (between D and G strings) to be back about 3mm or 1/8" from the scale length (in this case 25.125"), which should give the high E string 1mm of compensation or less, and the low E a little over 3. I think that was it, anyway.

Head over to the MIMF library and look through their stuff on bridge placement/saddle placement for acoustics, though, since I'm a bit of a n00b myself when it comes to building 'em. My first intonates spot-on, though.

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I put an acoustic bridge on a solid body about a year and a half ago. Not knowing any better, I just measured the scale at the high E and bumped it a touch forward. Complete guesswork. Surprisingly, it came out ok. The thing had other issues, so it's back in pieces waiting to be finished again. :D

If I'd known about this place beforehand, I'd have saved myself a lot of trouble.

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