I'm a first time poster to this forum, but have read it and Frank's blog for awhile now.

I have a question that seems like it could be addressed by you fine folks. I have a 1966 Martin D-18 that has had alot of work done to it. That I know of: the neck has been reset at least once, the bridge has been moved (if not replaced), the saddle has been shaved, and the frets have been dressed. When I got it the A string was extremely flat past the third fret. I changed to 3 different string brands thinking that the strings were the culprit. Not the case, all of the other 5 strings tuned up and intonated just fine all the way up past the 14th fret, but the A string was still bad. The first 3 frets are golden, and I can play cowboy chords all day long, but as soon as I move up past the 3rd fret it all gets shot.

I took the guitar to a repairman who said the bridge was in the wrong spot. He made the proper measurements and moved the bridge and still found the A to be flat and exhibit the same symptoms as before. He then built a "shelf" to try and accommodate for the flatness at the bridge. This helped a little bit, but I still can't play it past about the 4th or 5th fret depending on the chord I use.

So, I ask you guys. What could be the culprit? Has anyone dealt with anything like this before?

Here are a few pics for reference:

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Very difficult to tell whats going on here without the guitar in hand. It looks like the shelf isn't doing much at all there, if the end of the string length is at the end of the shelf that would be a huge amount of adjustment to make for an intonation problem. It's obvious that the bridge has been off a couple times on this instrument, and in the second photo still doesn't appear to be positioned correctly. The lateral string spacing looks shifted to the bass side considerably, you've got almost no space between the 6th and edge as opposed to approximately 1/8 on treble (again, hard to tell, maybe it's the photo angle). If that's the case it's probable the neck was re-set poorly. Looks like a job for another repairman.
From the pictures I would say that the bridge is quite definitly too far forward. There should be a sizeable gap between it and the pickguard, and the finish line behind the bridge also seems to indicate that it was further back in the past.
Before you go any further, you really need to establish as to whether or not the scale length is correct, you could measure it yourself using this:
It comes with full instructions, and is very accurate. I use it a lot in my shop, and it's suprising how often instruments have the bridge glued on way out of whack. Once the bridge is in the right position, it's no big problem to make a compensated saddle: I can play bar chords all the way upto the 12th fret on my 6-string, and the 12-string too: I made a fully-compensated saddle for the both of them, but it can only work if the bridge is in the right position in the first place.

You can't tell anything by the pickguard, because it has obviously been replaced (by one that's supposed to fit a style 28 rosette). If the second picture is straight-on, the 14th fret appears about 1/8 inch away from the body edge. If so, the bridge may very well need to be way forward like that.
Possibly the fingerboard has been replaced. I have encountered another Martin with the same issue, a late 40s 000-28. In this case it was clearly a factory error. The bridge had been relocated by a previous repair; I was dealing with the cosmetics and resetting the neck:
Like the man says check the scale lenth first before you do any more messing with it . Bill. """""""""""
The nut ceases to have any effect once you fret the string.

Millions of Martins inotate fine with a straight saddle. there is no reason this one should not.
If all the other strings are fine (12th fret harmonic =12 fretted) then the bridge has to be in the right place. and should not need this shelf.
There has to be some problem at the nut end but I doubt that it can be diagnosed over the net, Find a better Luthier than th one you went to.
Thanks for all the suggestions guys.
Here is a pic of the nut and headstock, though I doubt it will really tell you anything:

I can't tell that the neck is authentic.Something about the cutout behind the nut...and the nut does "appear" to be shifted toward the bass side. Plus a '66 should have been better cared for.You can probably adj. the length at the nut as others have suggested.Now even the body shape doesn't look like a D to me unless the pic is a little skewed.Somebody's been pickin' everwhere but on the strings!!!
I really have very limited info about the guitar's history.
The comments about non authentic pieces are a little concerning to me, though.
I'm no expert but what I meant about the body is it lokks more like an S style.


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