This project has gone through several versions starting with my first attempt at a floating shelf. What I found was the number of shelves I would need would put far too many holes in the wall, two per shelf, for my comfort so I came up with an idea to affix floating shelves to a back piece and have to only use two nails for each assembly.
The tools I used were:
Model Miter Box
I recommend the individual shelves be made first and then used as a reference to mark the distances on the back piece.
I forgot to add a photo of the holes used to attach the entire shelf to the wall. There should be two one at the top, between either the first or second shelf, and one at the bottom between the last or second to the last shelf.
This is the thickness of the individual shelf.
I got ahead of myself and painted the back piece before gluing the cross piece into place.
I used black contact paper, with a thin layer of glue, to cover the sides of the shelves. The materials used change as I improve the project and find better methods. The models weight 4 ounces each and I have not tested any heavier than that.
In the third picture you can see the materials I used on my first two attempts wood on the left and foam core on the right.
This project can be modified in both size and number of shelves as well as types of materials.