I have a recessed wall and want to build in some shelves. Went to the lumber yard today and got some 1"-thick hard maple boards and asked them to mill them down to 5/8", which they are going to do tomorrow, and then mentioned it to my dad, who said I should go with at least 3/4", and I can still call and leave them a message and change the order or tell them to hold it. But I would really like them to be thinner.
The shelves are going to be 8" deep and 4' wide, and ideally should be supported only at the ends and not bend visibly under the weight of the books. If anyone can venture an educated guess how much they would bend at 5/8", 11/16" and 3/4", I would appreciate it.
I may have learned this in the strength of materials class, but I barely remember anything from it and it was not my favorite subject. Formally, I think, this would be called maximum deflection of beam with two supports. I can't find the formula online and seem to remember vaguely that the deflection is proportional to the beam thickness to the third power. Does that sound right?