Here is a little trick I learned from Beau Hannam (Luthier extraordinaire). When shaping a neck one carves it to the final shape but there are still little inconsistencies. To straighten these out one makes a sanding block that is just shorter than the straight part of the neck. I use PSA sticky-back sandpaper to stick onto the block. You mark pencil lines all over the neck and then sand with the block cross-wise to the neck.
The pencil lines gets taken off where they are the high spots, and the low spots are revealed as remaining pencil lines. Keep sanding, maybe giving the high spots some extra attention with a file.
Almost done, only one little low spot.
All done. An easy process that makes the necks feel better under the hand because they are absolutely level and consistent.
