Getting close to gluing the neck on. I need to make one more check, and I need to get the dovetail to fit well.
Aside from the set (pitch, or angle) of the neck being correct, the neck also needs to be centered correctly. It's easy for it to get off-centered with all the hacking away that's been done to the heel.
Then I used a straightedge to see if all the marks lined up. If they don't, you'll need to adjust one side or the other of the heel (i.e., take a bit of material off) to get it to align.
In my case, I was off by a small margin initially - maybe 1.5mm. I just 'tilted' the neck (side-to-side) to line it up and from that, figured out where material needed to come off.
If you don't do this, there is a high probability that the outer strings won't lie correctly on the fingerboard - one side will be too close to the edge or may even fall off.
I have a nice block of mahogany that I use for braces, patches and shims. I cut a sliver and used double-sided tape to hold it onto a piece of scrap. Then I sanded it to thickness on the belt sander.
How did I know the thickness to shoot for? I had used some paper card stock in the neck joint as a test to get an approximate thickness. Then I measured the thickness of my paper shims - .018 of an inch. With that thickness of shim, the neck didn't quite sit all the way down into the joint. Which is ok.
Mahogany is really nice to work with. I love it. It works easily, it's strong, it looks good, and it smells great. What more could you ask for?
I stick carbon paper into the joint and then push the neck down. This is a bit tedious - it took at about 15 or more fittings like this to get it accurate.
I used long strips of carbon paper held onto the guitar with drafting tape. You're seeing top side here - the strips bend down into the joint.
After a number of rounds, the neck will fit all the way down into the dovetail and be tight.
I marked the frets onto a block of wood, then chiseled out grooves. The block is also radiused a bit to fit closely to the curve of the fingerboard.
I'm finding that making custom jigs and cauls is a lot of fun. At first I wanted to rush to get them done, but now I find myself trying to make them look decent.
Here it is clamped up and preparing to dry overnight. Note the caul inside the body at the top of the soundhole. Guilds have a fairly large brace there, so I cooked up a caul with a groove to fit over it. I'll reuse the caul on the two other Guilds I'll be working on as well.