I made a jig using a 5/8 drill on a drill press. I drilled 5/8 holes every 1
1/4 using a fence and an indexing peg. The jig is 4 feet long. I added a
tailpiece that was threaded so I can index at the bottom of the work piece.
The jig was 6 inches wide and the holes were drilled 2 inches on center in
from an edge. You can align either edge against your work and get a 2 inch
or 4 inch inset. The jig took a couple of hours to make and the hard parts
were the edge guides and tailpiece.
Oh yeah, you use a plunge router with a 5/8 template guide. You can use 1/4
inch spiral or 5 mm or whatever size you want in the router. I then drew
lines through every other hole so I can choose to skip a hole of use them
all.

max

for a bookshelf, anyone have an opinion on which type of adjustable
shelf support to use?

The metal rail with clip is out of the question for this project.