[QUESTION] Relationship between truss rod, bridge height and action

Action & bridge heights are directly correlated, truss rod-usage only sideways. The trussrod dials in the relief (curvature) of the neck, necessary for the string to vibrate freely without slamming into the frets creating buzz. There are "manufacturers opinions" regarding how much relief there should be, but in the end it boils down to your personal preference, how you play and what strings you use. If you use heavy strings and hit them like a gorilla on steroids, you're going to need a bit more relief than when you play with very light strings and stroke them with a feathery touch.

Action & bridge height are directly correlated. Since the bridge sits twice as far from the nut as the 12th fret, you can use trigonometry to get in the right ballpark. For example, with the relief already dialed in to your preference, if you have an action of X mm at the 12th fret, and you want to lower it to X-Y mm, you have to lower the bridge 2Y (so if you want one mm closer at the 12th fret, it means lowering it 2mm at the bridge).

Also a factor that is often overlooked is the fretboard radius. A curved fretboard requires a bit higher action, to offset the fact that the fretboard curves towards the string (you may have an action of 2mm directly underneath the string, but that can become 1.8mm when you measure a bit closer towards the middle of the fretboard). The flatter the radius, the lower you can make your action without buzzing.

In your situation, a relief of 0.010" (0.25mm in non-retarded units from the top of my head) is a good starting point. A little fretbuzz doesn't hurt (especially when playing electric, and it doesn't sound through the amplifier). What I would do is revert the straightening of the neck back to 0.010", and lower the saddles a bit. That should give you a lower action without buzzing at the 7-10 position. For sustain: use heavier strings. Heavier strings have more mass, more mass dampens slower, thus increases sustain.

the buzz being local to the 7th -10th frets suggests to me that you do need some more neck relief

If you want low action as possible you should have a flat neck (little to no relief) and frets should properly be leveled.

Its hard to say what causes buzz in a guitar really, a basic rule of thumb is lower frets are due to having a tight truss rod and higher fret buzz is because of low saddle height but no matter how "perfect" you setup your truss rod and saddle height it won't matter if you're frets are not properly leveled. This is most apparent when you go very low action.

Good info in here already. I'm a bit of a shred guy myself, when I set up my guitar, I gradually tighten the truss rod and retune, until there is no relief. Then I back it up just a hair. This is a good way to get a very flat neck.

Similar idea for bridge height; lower it bit by bit. Retune and play around after each time. When problems arise, back it up a notch. My live guitars usually have just under 1mm action.

It all relates to the whole of the guitar setup but certain things are done for certain reasons/outcome.

Adjust the truss rod ONLY to set the desired neck relief. Forget the action and everything else. Only think of the truss rod in terms of setting the neck relief.

Will adjusting it affect the overall action? Yes, but that is not why you adjust a truss rod. Once the rod is adjusted as desired, then pay attention to the bridge and nut height. I'll put the bridge action where I want it, then the nut if needed. The reasoning is that the bridge is capable of the bigger range. Then I address the nut action, then retweak the bridge if needed. Unless the nut is obviously way out, then I might start on the nut if the bridge is at least in the ballpark.

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Use a credit card edge across three frets at a time and see if the card rocks. Check all frets on all strings, use a sharpie on the top of the fret to mark high points you find. Do these match where you are getting buzzing (most likely)? A fret level will help a lot.

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I think very low action, strings touching the frets, sounds horrible and very thin, no sustain bc there's no room for the strings to vibrate. It may sound okay with heavy distortion, but clean it sounds like dog crap. Here's an example, you can hear how low his action is, that it's choking the sound of the strings.

[ low action ] ( https://youtu.be/-E49h1V12yI )

You need to take all the strings off and take a straight edge and put it on top of the fretboard. Tighten the truss rod all the way until the neck is dead straight then put the strings back on and adjust action and intonation. Fret buzz and how low you can go will depend greatly on the quality of the guitar. Usually the better quality instrument, better fret job and finish of the neck is done, which will give you lower action. Go slow and one step at a time, it's not difficult to do.