It’s pretty much standard practice for me to adjust my guitars twice a year. I’ve learned through a bit of trial and error just how much of a tweak my primary guitar, a Martin M-36, needs in the spring and again in the fall. I purchased a special wrench directly from Martin for this, which is longer than a standard hex head wrench and easy to use with Martins that have both the traditional dovetail joint holding the access point to the tension rod and the more difficult to access rods on Martins with mortise and tenon neck attachments. It’s a good investment if you have a Martin.
I also have a similar tool from Taylor that also works very well. For Gibsons I use a standard hex head wrench as the rod is accessed from the head of those guitars, beneath the truss rod cover. That is a more difficult adjustment to make as the truss rods in Gibsons always seem to be more reluctant to turn.
This adjusting process can be maddening because the results are so variable. Here are a few things to remember if you decide to attempt it.
First, if possible leave at least a few of the strings on the guitar so the neck is under pressure. Removing all the strings certainly makes it easier to access the end of the rod via the sound hole (assuming that’s the way its done on your guitar) but it’s almost pure guess work as to how much angling the adjustment will result in when you put strings back on and the neck is under pressure. Also – be patient! Turning clockwise results in less relief (more of a backward bend) in the neck and often all that’s required is perhaps a quarter of a turn. Do that and retest the action. If more is needed, try another quarter turn. Do NOT be aggressive and crank the poor thing a half dozen times because you could seriously damage the threaded portion of the truss rod, making it impossible to adjust at all and requiring a serious repair.
When adding relief to the neck (loosening the truss rod) don’t be surprised if the guitar takes some time – perhaps a few minutes or longer – to react. The wood in the neck will respond slower to loosening of tension. Again, be patient!
The action on your guitar is a personal thing. We all want it to be as low as possible but without annoying buzzes when played and that depends to a large part on how you play. If you’re an aggressive player who strums hard you must live with higher action; if you’re a finger style player who has a soft attack you can usually get away with low or “fast” action. Height of the saddle comes into play too but sanding down a saddle is something best left to a qualified guitar tech. Tweaking the action via the truss rod is worth a try if your guitar changes with seasonal temperature and humidity variations, but use care. And take your time doing it!
Peace & good music,