A jig of one sort or another helps gauge the neck’s alignment—no easy task given that three dimensions are involved: (a) the center line of the body, (b) the longitudinal plane of the body, and (c) the horizontal plane of the fingerboard.

Final fitting is done after the body assembly is complete.  Once within 1/16th inch of the heel I stop. Lubrication from the glue and pressure from a C-clamp do the rest.