Step 1: Neck relief
This is the foundational adjustment. You must begin here.Tools Needed:
The neck of your guitar or bass cannot be too straight, nor can it be too bent. You must have just the right amount of bend, or relief, for it to play right. How do you know if you have the right amount of relief? You measure it.
There is no shortage of how-tos available on the internet that will tell you that you don’t need any tools for this, that you can do it with a quarter, a business card, a credit card, or just “by feel, man.”
This, in my opinion, is ridiculous. You’re seriously going to put countless hours into learning your instrument and hundreds if not thousands of dollars into your gear, but you can’t be bothered to buy and use the correct tool to maintain it? Absurd. You can get feeler gauges for $7 on Amazon and they are available at literally every hardware store in America. Get them. Use them. There are no excuses.
On to the correct way. We’re going to measure the neck relief using a capo and a set of automotive feeler gauges.
Hold your instrument in playing position and capo the first fret. With your left hand, fret the low E string at the fret where the neck meets the body. Cross your right hand over and insert a feeler gauge (8-thousandths-of-an-inch for gutiar,12-thou for bass) between the E string and the fret wire of the 7th fret. What you’re looking for is that it just fits between the fret and the string without lifting the string at all. You’ll have to do this carefully and give it a few tries to make sure you’re inserting it flat.
If you can fit the 8 (or 12) thou gauge in with room to spare, try the next largest feeler gauge. Keep going until you find one that just goes in without lifting. That is your neck relief.
If you can’t fit the 8 (or 12) thou in without lifting the string, try the next thinner one until you find the one that just fits. That is your neck relief.
Now what? If your neck relief is above 8 (or 12), your neck is too bent and you’ll need to adjust your truss rod by turning it clockwise. If your neck relief is below 8 (or 12), you’ll want to adjust your truss rod by turning it counterclockwise.
Adjust your truss rod using 1/8 to 1/4 turns, retuning and measuring the relief after each small turn, until you arrive at your destination. Some truss rod adjustments are made at the headstock, some are made at the other end of the neck. Some instruments even require you to remove a pickguard or even the neck itself to get at the adjustment. And make sure you use the correct tool for the adjustment. Most will use hex keys or Allen wrenches. Some of those are metric, 4 or 5 millimeters, and some are imperial, at 3/16ths. Do not confuse metric and imperial. You could strip the truss rod. If that happens, your instrument may be toast.
Is 8 (or 12)-thousandths-of-an-inch a magic number that everyone agrees on? No. But it’s a good rule of thumb for most makes/models of electric guitars and deviating more than a couple thou may result in the instrument not playing correctly. Check with your manufacturer. Also, I view most of the values in this guide as a starting point. Me, I like to get my action as low as I can with my bass guitars. In some instances that leads me to a neck relief of as low as 8 thou and a B string height of as low as 4.5. Not all instruments will play correctly like this. Not all players will want this. The numbers I suggest in this guide are reasonable average values to start with. Then, as get to know your instrument and your playing preferences, you may want to deviate from them.