A couple of years back, I needed a cabinet in my radio room to fill a small gap and utilize some wasted space. I bought a couple of junked-out book cases for a few bucks, off marketplace. The build can be seen at https://wb4iuy.blogspot.com/search/label/Cabinet
The shelving is partical board. With the weight of radios, they began to sag. I bought somecheap aluminum plyboard edging from Ace Hardware. This is a "U" shaped extrusion. I drilled holes in the center, and attached it to the lower edge of the shelving with wood screws. This straightened the shelving, and reinforced it for the heavier load.
