I like to have my necks dead straight (using a straight edge) when there's no string tension, then when you tension the strings this will introduce a small amount of relief naturally. It depends on the the amount of relief the neck already has, the best way to check it would be to use a metal/aluminum straight edge to check it, failing that you can use the strings themselves as a straight edge of sorts, fret at the first fret and the fret where the neck joins the body +1 (usually about the 17th), there should be a clearance gap about the thickness of a business card between the bottom of the strings and the top of the fret at the halfway point (usually about the 8th or 9th). Is it best done with a truss rod adjustment, and if so, do I need to take the strings off to adjust it? I am curious as to how to lower the action on my Casino.
