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I want to try a neck reset on my '96 Martin DM. But I'm intimidated by the sound hole access truss rod. Will it interfere with neck joint? I can't find any drawings of the construction. Is this a mortise and tenon rather than a dovetail? I've been deeply disappointed with this guitar! I guess it can't take the tension of 13-56 strings. I've already had to re-glue the bridge plate. Stringbender

It's a glued mortice and tenon. The truss rod will not be an issue it's internal to the neck now that it's under the fret board and simply comes off with the neck.

The fret board extension is glued per convention and needs to be released first. The wooden plate in the sound hole on the neck block is firmly double stick taped in place. We use bent in U shape putty knives to work under the plate and eventually get it to release. Be careful the plates do break in half if you try to pry too hard.

Next there is a bolt in there under the plate, may be two I'm not remembering this early in the morning. If the extension is fully released (fretboard extension) the neck should come off when the bolt(s) are removed.

Setting the neck angle is the same method as we do for a dovetail joint judiciously.... removing specific and minimal material from the neck heel cheeks until you have a gapless fit, it's in alignment left to right AND the neck angle is properly set. There is a lot to this if you have not done it before.... be warned. Fret dresses after resets are advisable too.

The neck is reinstalled with glue on the tenon and under the extension and the bolts snugged up. It's been said that the bolts are really only there to hold the neck on until the glue dries but the glue joint does fail on these leaving the bolt the only thing holding the neck on. It is what it is.

This is a Mexican Martin and was a lower priced offering from Martin. They do need proper humidification or all things can go wrong with them just like any other acoustic guitar.

PS: I wanted to add that 13's though very common are hard on a guitar more so than 12's in so much as there is not only more tension 13's are often set with slightly higher action which adds rotational forces to the bridge.

DM's were lightly built likely to be responsive but if an instrument is too lightly built they start to fall apart.

Good luck this is one of the most difficult things that professional Luthiers do, neck resets. There is FAR more to it than I offered above so be warned.

Much thanks to Hesh for your advice. I've removed the wooden medallion and the One neck bolt it was hiding. Also discovered that the neck block is not even one piece, but a glued laminate of over 2 dozen 1/16 pieces. Also, correction to my original post, I re-glued the Bridge, not the bridge plate. The top was so extremely bellied up that when there was no more give the strings began to pull the bridge off. I plan to do a complete re-fret and want to play around with nylon strings.I am mostly a player who builds for need. I have built two quite successful archtops, and done several complete re-frets. But this will be my first major effort with a flat top. Stringbender