"Stephen M" writes:
"blueman" wrote in message
...
I'm building a bookcase with adjustable shelves with a 46" span that
will likely carry some heavy books.

That's pretty big span

To cover the load, I am making the shelves 1.5" thick (double 3/4"
plywood).

Plywood is not the most deflection-resiting material as half of the plys are
going the wrong way to help. Solid wood will perform better. If I were you I
would try it out an see how much deflection wou get applying hand pressure
to the center of a test-shelf.

Well, I plugged my dimensions into the "Shelf Sag Calculator"
(www.woodbin.com/calcs/sagulator.htm) using the following parameters:
Species: Plywood, fir (only plywood choice)
Weight Load: 200lb, uniform load
Note: this seems generous given that per the note, they
claim that a fully loaded bookshelf weighs 20-25lb/foot.
Which for me would have given a maximum of 96lbs.
Width: 46"
Depth: 12"
Thickness: 1.5"

The resulting maximum deflection was 0.06" which is about
1/16". Again, according to the notes, the eye can recognize a
deflection of 1/32" per running foot, which would translate into 0.12"
in my case of a 46" span, again well within my tolerances.

For comparison, a "standard" 36" wide Eastern White Pine bookcase with
8" depth shelves under a load of just 25lb/foot would give a
deflection of 0.13" or more than TWICE as much as my design.

ALSO, I am going to be giving each shelf a front edge facing of
1.5x0.75" poplar which should add strength, I imagine.

Assuming that all my calculations above are correct, I am now most
worried about shelf-pin tearout which is why I was thinking that the
wider pin (1/4" vs. 5mm) and the sleeves might help