The bodies are completed, with binding, and sanding, and sanding, and sealer, and sanding and sealer, and … you get the picture.
The one remaining step before the bodies can go to the finishing closet is to fit the neck heel to the body. To get neck to fit up against the contours of the body I have made a jig that clamps the body down along a center line, and then has a sliding setup for the neck, using the slot that will hold the carbon fiber reinforcing bar up the center of the neck as a center reference. The slot is 1/8 inch wide so I fit it over a set of 1/8 inch brass pins. The neck is pulled into the body with a spring and held down with some barbell weights. Then a piece of sandpaper is run between the body and the neck, with the sanding side towards the neck. The sandpaper is pulled back and forth sanding the neck end so it exactly matches the body. A bit of work/exercise but rather simple in concept.
I use a bolt-on neck. My old design used a barrel bolt, which is a round steel dowel with a threaded hole.
A hole was drilled up through the heel to hold the barrel bolt, and the threaded part came through the body into the neck.
This design had a weakness, which showed up twice. Since there is a hole up through the heel, and the heel is not very big, there is relatively little wood in the middle of the heel. Add to this the fact that the wood grain is running straight through the heel and you get a weak area and the heel cracks along the red line. Once this happened in shipping (they must have dropped the instrument from quite a height onto a concrete floor or something) and the other time the instrument was accidentally kicked off a stand on stage. In any case, I have re-designed how I do the bolt on.
The new design uses a threaded brass insert. I glue an oak dowel up through the neck heel so that the threaded insert is gripping the side-grain of the oak dowel, and the oak dowel grain is running cross-wise to the grain in the neck itself making this much stronger.
As a test I made up a sample neck, bolted it to a simulated end-block, and dropped a 3 pound sledge hammer some feet onto the outer end of the neck. It just bounced off, no damage at all.
To get the brass insert at the right place, and straight into the neck, I have a little jig that centers the neck using the slot that will take the carbon fiber reinforcing bar to fit over some brass pins. This jig has a block on the end which has a hole of the size for the insert drilled exactly along the center line. A drill bit is inserted through this hole and the hole for the insert is drilled into the neck.
Without moving the neck, the brass insert is then threaded in, using the same reference hole in the jig to ensure that the insert goes in straight and true.
Then finally a center is threaded into the brass insert and the neck is placed back on the jig used to sand the heel profile to fit the body, and the neck is whacked against the body to mark the exact spot that the hole should be drilled through the body for the attachment bolt.
Now one can glue in the carbon reinforcing rod, glue on the headplate and fingerboard, and shape the neck.