NGD - SJ200

[Dave F]

3 hours ago, Joe M said:

Sorry, Buc, guess I wasn’t too clear. What I meant was, unless I’m misunderstanding the whole thing, why would a builder under or over set a neck, wouldn’t he want it perfect always, or at least as close to perfect as he could make it.  

I had a custom L00 built and I like my action very low. I instructed the luthier to overset my neck so that when the action is lowered, there is still plenty of saddle exposed and the the height of the strings above the body is more desirable. If I take a perfect neck set (the top of the frets even with the top of the bridge (not the saddle) and lower the action to my preference, there's not a lot of saddle above the bridge. And if the neck is underset as Buc mentioned, there's not enough saddle to lower the action to my preference. Throw on top of that the tapered bridges that are higher on the bass side  by design and you get a new twist. I've own a few AJ's and they all had the tapered bridge. Most Martins have this too. I understand the concept to have the bass strings higher so they have room to vibrate without buzzing the frets while doing heavy strumming to achieve louder output such as in bluegrass. bands. 

[Jinder]

9 hours ago, Joe M said:

Sorry, Buc, guess I wasn’t too clear. What I meant was, unless I’m misunderstanding the whole thing, why would a builder under or over set a neck, wouldn’t he want it perfect always, or at least as close to perfect as he could make it.  

Sorry to jump in on this-necks are never intentionally underset, that is something most would class as a build error. Neck sets vary as with handbuilt instruments it's an imprecise science, but to my mind a properly made acoustic guitar should have a 30yr run before it needs a neck reset. 

Most guitars have two phases of geometric settling, the first being in the first three years as the guitar adjusts to no longer being a tree. The parabolic arch of the top forms to some degree (Gibsons are built with a parabolic arch, others not), finding its limits of flex under tension against the constraints of bracing, kerfing etc. The neck angle will change slightly in correspondence with the body shape settling, and the most common symptom of this is the action coming up a little as the neck settles in and the top arches a little, bringing the bridge higher. 

At this point, most properly built guitars will have plenty of saddle left showing above the bridge and can have the saddle height reduced accordingly to lower the action. An underset neck will often make this impossible, leading to "bodge job" solutions such as shaving the bridge itself, planing the neck diagonally (which actually affects intonation by way of making the scale very (very!) slightly longer) and so on. In this situation, the guitar really needs a neck reset.

The second phase of settling usually takes around 30yrs or so of playing and living under tension and in changing temperatures and humidity levels...normal existence, as it were. It's a very gradual process, and usually involves a Spruce top fully curing and the sap in the wood itself crystallising, which leads to the top shrinking slightly and the guitar changing shape accordingly. The bridge area usually develops a belly over time (I've heard several bluegrassers claim a Martin dread sounds at its best "when it's old and looks pregnant"!) And this can all lead to a further increase in action, necessitating a neck reset for the sake of playability.

Some guitars will need a reset sooner, some won't at all. I have a 1967 J45 which has an immaculate neck angle and excellent action, even at 52yrs old. I have a 22yr old D18GE prototype which is similarly perfect. A 25yr old centenary year Blues King which is also geometrically perfect. However, I owned a Dove not long ago which changed shape so drastically it needed a reset after I'd owned it for a year.

Wood is wood, and as such is highly unpredictable stuff. A correct neck set goes a LONG way towards offsetting that unpredictability, though.