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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
Do the same thing to the back of the shelf that you are doing to the front except use a less expensive hardwood.
Rick
A 1"x1/8" steel bar is your best option. The steel bar will be mounted inside the nose and shelf. Google "long span bookshelf steel reinforcement"... there are some pictures of people using this technique.
Thickness is good. The stiffness of a shelf goes up as the cube of the thickness. That is, if you make it twice as thick, it is eight times as stiff. So adding another 1/4" of plywood adds quite a bit of stiffness. If you can add a full 3/4" of thickness, you'd be in fat city.
How are you attaching/connecting the shelves to the side of the bookcase?
I have done long lenghts too.. what I've done is to put clips at the back of the shelf just like the sides.
That avoids the sag...
Good Luck
Joe
+1 for the steel bar
I have several 48" shelves with a 3/4 x 2" nose. They have been crammed with books for over 10 years with no noticeable sag. I also have a dozen 36" shelves with a 3/4 x 1 1/2" nose that don't sag. I'd say you could beef up the nose a bit, or add a similar piece to the back of the shelf like the one on the front. Your books will still fit (they have to fit under the front nose anyway).
See the world famous sagulator: http://www.woodbin.com/calcs/sagulator.htm
using 30 # per lineal foot, floating shelves @ 39" x 12", and oak for the hardwood nose, it just........barely........fails. At 28# per lineal foot, it hits the target max deflection dead on.
28# per lf means 91# per shelf, evenly distributed.
I can't remember which supplier has them, but one of them has aluminum channel that slips over the outside edge to give more support.