(Pictures to follow soon)
A major requirement of this process is to make sure that the neck & fingerboard are in their final position i.e the neck has been glued into the pocket of the guitar body, all the way down the pocket as far as it can go.
Because a Set-In Neck is glued into the pocket of the body instead of bolted (more on that in this blog post), we are unable to pre-drill these holes for you & thus you will need to manually determine where to drill these bridge & tailpiece holes. Set-In Neck guitars are known to be a more difficult build for this very reason.
You're going to start by placing a long ruler (the longer the better) along the side of the fretboard & down the body of the guitar. Draw lines with a pencil along the inside of the ruler thus creating an extension of the neck. Do this on both sides of the fretboard. If you have already finished the guitar then apply some masking tape to the body before adding the pencil lines. If the wood is still raw & you plan on painting it, then there is no harm in drawing on the wood itself.
It's also good to note that the useful part of a guitar string is the part between the string nut at the top of the guitar neck & where the string bends over the bridge saddle towards the bottom of the guitar. This length is essentially your scale length. We do not measure the string length though because there might be slight variances due to saddle positioning. Instead, we measure along the surface of the guitar.
In order to place the bridge saddles in the correct location, you're going to have to hold the ruler on the 12th fret (on the actual metal piece, not in between the two) & then measure the distance from here to the inside of the guitar nut at the top of the neck, where it meets the wood. This number (commonly converted to inches) & doubled is essentially your scale length. The 12th fret is essentially the half-way mark between your nut and where the bridge needs to sit.
If this length from the nut to the 12th fret is for example 32 cm's (12.59 inches), then measure 32 cm's from the 12th fret down the body of the guitar and place the bridge at the end of the ruler in its correct position & with the saddles as close to the end of the ruler as possible. This is where the strings will bend over the saddle.
The saddles of your bridge piece allow for some play in both directions to account for any variances once installed, so it's important to make sure that the saddles are positioned to the middle of the bridge so that when installed you can have some minor movement/adjustment both ways.
The bridge should also be proportionate to the lines you drew earlier, thus dead inline with the neck. You can do this by eye.
Once you are satisfied that the bridge is in the right location, you can mark the holes with your pencil. This is where we will drill.
If you are installing a Tune-O-Matic bridge, it is often tilted slightly on the bass side, by roughly 3 degrees or so. If you decide to angle to bridge, mark the new holes with the bass side (thicker strings) tiled slightly down towards the butt of the guitar.
Now its time to drill the holes. Make sure you correctly identify A) which size drill piece you need & B) what depth you need to drill so to avoid going through & out the back of the guitar body. It can help to measure the stud that you'll eventually knock into the holes against the drill bit & mark off the depth with some tape so you know when to stop drilling. You'll also want to rather drill a hole that's slightly too deep than slightly too shallow, to avoid the stud not going in all the way and having to pry it back out of the body.
If you're using a press drill, a good way to make sure of depth is to align the pickup cavity under the drill & with the drill turned off, drop the drill head into the cavity. It should fall into the cavity & not have too much movement left over that it would go out the back of the guitar.
Make sure the guitar is clamped or somehow secured. A mistake here could be costly!
Also if the guitar has been finished with a lacquer or custom artwork, its recommended that you break through the paint layer with the drill spinning slowly in reverse. Once you've broken through the paint then you can continue to drill like normal into the wood.
Before you knock in the studs in, rather test the depth of the holes because it's extremely difficult to get the studs out once they are in. Also, make sure that the holes are free of any sawdust or leftover debris.
For the same reason as above, some guitars are required to be grounded via the bridge stud. If this is the case (this is usually the case for guitars that have a back electrical cavity & Tune-O-Matics bridges such as Les Paul's, SG's etc) make sure you do not knock in the stud before first grounding it.
If you do need to ground: You will need to drill a small hole from the back electrical cavity of the guitar connecting to the bottom bridge stud hole. You will see that its not much of a distance. You will then need to feed a piece of electrical wire from the cavity to the bridge stud hole, fray the end that pops out the hole, wrap the copper around the stud and then knock it into the hole. The other end will ultimately be grounded with the components.
Once the bridge stud is knocked in you will now need a tailpiece. The tailpiece does not need to be an exact distance from anything as it only feeds the strings, but it also can't be too far back that the strings won't then be able to reach the tuning pegs. The usual distance is normally +-2 inches behind the bridge piece. Follow the same drilling instructions for the tailpiece & voila! In no time you'll have your bridge & tailpiece set & ready for mounting.