This is what is involved in cutting a custom nut..
1. Clean nut slot/ groove.
Make sure you keep it square!
2. Select nut blank, cut slightly longer than finished size.
3. Break out favourite new toy... Ummmmm... Tool and mill bottom edge square.
4. Mark fretboard height on nut
5. Then mark fret height then string height.
6. Begin cutting bevel on back edge before radius sanding the top profile.