National style tri-cone resonators have a very tight radius or arch to the upper bout under the neck heel.
Trying to contour the heel to fit properly is an exercise in frustration with hand tools.
My solution was to steal a tool from banjo makers and create a jig to transfer the body’s contour onto the neck using an oscilating spindle sander instead of a shaper or router .
I traced the body onto a piece of baltic birch ply and cut out the contour to create a guide. I then drilled a 3.25″ hole, aligned to the outer edge of the contour on the center line of this guide template.
With the sander drum aligned to the outside of the hole, the guide template is then clamped to the top of my oscillating drum sander.
I then matched a second piece to that contour and added 1/4″ centering pins (that fit in the truss rod slot) and a clamp that allows me to align the neck to the movable base guide. The only part of the guide and template that needs to be an exact match to the body is the 2-3″ in the center of the arc under the heel; which is represented by the pencil marks visible on the templates.
I align the outer edges of the neck blank to the inside edge of the base guide, and clamp the neck in place.
This jig allows me to then simply push the neck into the sander and after a couple of light passes, I can match the profile of the body to the neck.
Simple and easy. I imagine it will work with almost any slope shouldered instrument.