Brian-
On a couple of the racks I have done, including one that is supporting a 350lb turntable, I drilled 3.5" in from the front and back edges, and 1.5" from the sides - to the center of the rod. If you want to go to 3/4 as some suggest, you may need to adjust slightly.
A good rule of thumb is to keep in mind what will be housed on the shelves, and keep a minimum clearance for standard 19" width components between the rods/nuts/spacers....
On a couple of the racks I have done, including one that is supporting a 350lb turntable, I drilled 3.5" in from the front and back edges, and 1.5" from the sides - to the center of the rod. If you want to go to 3/4 as some suggest, you may need to adjust slightly.
A good rule of thumb is to keep in mind what will be housed on the shelves, and keep a minimum clearance for standard 19" width components between the rods/nuts/spacers....