I'm building a 39" bookcase. I'm using 3/4" birch plywood for the shelves, and will be using a 3/4"x1 1/4" nose out of solid hardwood to reduce sag.At 39", i know i am beyond the limit for a bookshelf .I'll be using standardswith 4 clips and nothing midpoint.Any ideas of how to avoid a midpoint support. I was thinking of gluing 1/4" ply to my 3/4" birch ply, to span the 39" without sagging. thanks rob