The process for making the neck-master is the same as the body-master. I drew a neck and headstock on paper and then glued it to the hardboard. Of course, you need to know what scale you're using and how many frets. Then, calculate the length of the neck and it's graduated width from nut to last fret. There are many books and sources for these calculations.

Drawing of neck glued to hardboard.

Here's the neck-master all trimmed and ready for final shaping on the spindle sander.

Neck master trimmed and ready for final shaping.

We now have a pretty good idea of the guitar's profile with the neck and body masters aligned and laid out.

Body and neck masters aligned.