what i do when i'm slotting my nuts, instead of cutting a pencil in half like that, i just draw the line right where the nut and fretboard meet, and then measure up about 3/32" and draw a parallel line, then i shape it. your method is very interesting though.
Man, I check this thread every day for updates! It's making me want to build one myself (although I'm wise enough to know it's not as easy as you make it look). Very nice work!
i was shaping a neck today, and i used a method inspired by you i used my disc sander to knock the back of the neck off flat after i notched it to depth on the 1st and 15th fret, and knocked off the excess with my bandsaw. it worked perfectly, and really made shaping the neck a lot easier.