Nice job Timbuck. Your process is definately more efficient in output than mine but at least I did solve the issue of getting a perfect fit without the need to sand. Here is a cut and paste from a post I had at UkeTalk a while back. This may be useful for those that don't have access to a lathe.
There are some things about the building process that you just can’t speed up. And there are those other tasks that seem tedious with variable results. Shaping the neck heel and tail blocks to conform to the curvature of the body is one of those small but dreaded elements that I never look forward too. I know that some builders just make their molds so they are flat at both the heel and tail but I prefer to preserve a shape that is a bit more true to the original Martin shapes.
I have the Ken Potts video where he shows how he “eyeballs” the space between the body and the block, transfers this to the block, and pencils in a sanding line. He rolls it back and forth over the belt sander and claims that eventually you just get the hang of it. Well, for my first 6 or so builds I could never get the hang of it so I decided to try something similar to what I remember seeing Mike DaSilva do back when he was in his small single care workshop.
Mike used a disc sander and a jig to shape his heels. Everytime I messed up a block I would tell myself I needed to make a jig like Mike’s. I finally threw together a quick jig for this purpose and it works great and makes this process a breeze. I actually made the jig a couple of years ago and have used it on the last two tenors and a couple of sopranos I'm finishing now.
It’s just a T fence that mounts to the table of the disc sander. A trammel is used to pivot on a ¼” dowel at the correct distance from the sander that will create the matching curve. To do that I just used a long scrap piece of particle board and using the molds I traced the curve near the end of the particle board. Then I had a 3/8” wide strip of wood that I drilled a small hole in the end to look through. Then by trial and error I just drilled small holes at the other end of the stick for a brad to fit in and sited through the hole until it matched as I pivoted the stick across the board. That would be the distance I would use to make my permanent trammel for the jig.
Here are a few pics. You rotate the work against the rotation of the sander. One pass is all it takes and it will conform to you mold beautifully.
The block is just screwed on from the bottom
Overall Setup
Feed into/against the rotation of the disc
Nice curve after one pass