Lube Your Nuts.
When I am out playing my old Bigsby equipped Gretsch guitar around town, other guitars often saddle up to me at some point of the night and ask about my tuning issues with the whammy bar (I think of the Bigsby as more of a goody bar myself, but that’s not the point).
Nearly as often as I am asked, they are shocked when I respond I don’t have any tuning issues.
When guitarists have tuning problems (which is to say, the guitar tunes up but in tune while playing or using the wham bar. Intonation of the guitar is another issue we’ll go into at some later date), it is usually blamed on the tuners, the whammy bar or the strings. The issue is most likely the problem in the guitar’s nut.
The nut is the angle changing point for the strings on the headstock. This angle is the equivalent of the string being fretted at the zero fret.
If the string is somehow binding in the nut, either because it was initially cut poorly or generally wear and tear, sweat and dirt had taken its toll on the grove, the tension on the string will be greater on one side of the nut than the other. This may (or may not) function fine for light strumming and less aggressive playing. But, lean on the whammy bar or do some strings bends…and boom! You’re out of tune.
What happens is that the tension shifted from one side of the nut to the other. When the whammy goes back to its rest position, or the bent string is released, to binding nut does not go back to the original un-even tension setting it had…and as we all know, the specific tension on a string between the nut and the bridge determines whether the string is in tune or not. Change the tension, you’ve changed the tuning.
By putting some kind of lubricant in the nut, the string can glide through the slot keeping the tension on either side of the nut the same. When the whammy bar is depressed, the lessened tension occurs on both side of the nut, when release it tightens up equally again: same tension, same tuning.
The locking nut which was invented as part of the Floyd Rose tremolo eliminated the problem by essentially having the string end at the nut. There is no tension exchange over the nut because the string is locked down.
A roller nut, little wheels with grooves in them for the strings, is another solution for the binding issue. The strings roll over the nut with no friction!
Some nuts are made of graphite, which is somewhat of a self-lubricating material. This is my personal favorite nut material.
However, in most cases, simply lubricating your current nut will solve your binding issue. There are a few products out there specifically for this issue such as Nut Sauce. I personally like powered graphite which comes in a small squeeze tube. You can find this where keys are made because it is typically used to loosen door locks. It can also be found at hobby stores.
Many guitarists and guitar techs use a graphite pencil as their lubricant and delivery system. They keep a very fine point on the pencil and simply run the tip through the string slot while they are changing strings. Neato! (Note that not all pencils are created equal. Most school pencils are not filled with graphite, but charcoal. Drafting pencils typically use graphite.)
You may be temped to use oil, such as 3-in-1 or WD-40, but I would avoid using those as the oil could stain your fingerboard. These could also change the tone of your strings, making the go dead.
In a pinch, a small piece of soap or dap of petroleum jelly (I’ve used Chapstik once) will do the trick. Remember that petroleum jelly is still oil, and the potential of staining the fingerboard and changing the tone of the strings.
If the lubrication doesn’t solve the issue (remembering that brand new strings need a chance to settle in), your nut may need to be re-grooved or even replaced, in which case you should seek the advice of a qualified repair tech.