Ours were done by drilling holes into the sides of the alcoves, the chap then fitted cut sections of threaded rod into those holes which protruded a bit. The shelves were cut to length and grooves routered into the ends. The shelves then slid onto these bolts. Solid pine 1.5" thick, I think. About 4/5' long and are rammed with books. Going nowhere at the minute.
Ours were done by drilling holes into the sides of the alcoves, the chap then fitted cut sections of threaded rod into those holes which protruded a bit. The shelves were cut to length and grooves routered into the ends. The shelves then slid onto these bolts. Solid pine 1.5" thick, I think. About 4/5' long and are rammed with books. Going nowhere at the minute.