Need advice building alcove shelves

[leem2837]

I know this kind of question has been asked before, but I've seen lots of conflicting information and am a bit stuck.

I want to build a series of fixed shelves in 4 alcoves, all of which are around 1 metre wide, and about 35 inches deep. I started building a torsion box shelf using 8mm MDF on the top, with 6mm on the bottom, but it still flexes quite easily checking with my hand.

I presume that my first stupid mistake was using two different thicknesses of MDF, especially with the thinner piece on the bottom. With a torsion box shelf, should I always use matching thicknesses? Also, if I need to put a fair weight of books on these, should I use the torsion box with MDF method, or timber?

I went for the torsion box for strength but also because my wife's quite keen not to be able to see any brackets etc, but I'm really not sure which way to go from here. Ideally I wanted it to look more traditional, so don't actually *want* the shelves to be too thick, but strength and safety are more important with two young kids..

Any and all advice would be great, I could do with making a start on these today but the more I read the more I'm confused.

 

[foxhole]

A thicker (around 30mm) mdf would be strong with a rebate to the bottom at rear and sides to accommodate a baton or ali angle on wall which would leave it looking like a floating shelf.

 

[Harbourwoodwork]

If its too thin it will bend over that width ,lipping on the front edge will stiffen it up