How to intonate a guitar with a floating bridge
This stems from a conversation I had in email recently, and it does make for a good article since not too many guitar players know about this.
My definition of a floating bridge is one that is not fixed into place. This means the only thing holding the bridge down is the strings and absolutely nothing else.
Above is a guitar that I think still uses a floating bridge, the Gretsch G6120T Limited Edition '59 Nashville. Since it has '59 in the title, I'm assuming it's built to vintage spec and has the floating bridge on it.
Most guitar players freak out when they see the floating bridge because they're so scared to move it for fear of completely wrecking the guitar's intonation. This is why there are so many articles out there that say, usually very loudly, ONLY CHANGE ONE STRING AT A TIME SO YOU DON'T MOVE THAT BRIDGE.
Any hollow body guitar that has a floating bridge does in fact have a guide built in to tell you exactly where to place it. It's right in front of your face. The F-holes.
In the middle of both F-holes are two points. One inner, one outer. The inner one literally points to exactly where you place the bridge. That's where it's supposed to go to achieve proper intonation.
However, it's not always universally true that you set the bridge exactly straight.
How you position the bridge depends on the type of string set used.
If using an acoustic style string set with a wound G (4 wound strings, 2 plain), then yes you can usually set the bridge straight and the intonation of the guitar will be fine.
If on the other hand you use a string set with 3 wound strings and 3 plain, then you'll probably need to lean the treble side of the bridge slightly towards the neck to accommodate for that plain G string.
I've seen other electric guitars where the F-hole middle point doesn't line up with the bridge at all. Why?
Whenever you see a guitar with the F-hole in the totally wrong position where the middle point is nowhere near the bridge, that simply means the F-hole is decorative and serves no other purpose.
An example of a guitar with the F-hole in the wrong position is the Fender Telecaster Thinline. The middle point of the F-hole is over the pickup and not the bridge where it's supposed to be.
Why does Fender make the Thinline that way? Because it looks cool. No other reason. Some may argue that the F-hole allows the guitar body to have more acoustic resonance, but that's a bit of a stretch to say that when compared to a full hollow body with properly positioned F-holes.
This isn't to say Thinline Telecasters are bad, because they're not. I owned two of them previously and liked them both. But I know the F-hole is in the completely wrong position on that guitar.