plywood bookshelves

[Vlad]

Hi all,

I am planning a couple of bookshelves to be made from a 1/2 inch plywood,

35x11 inches in size; some shelves will be fixed in 1/4 inch deep dadoes in the sides of the bookcase and others will be "floating", supported by pins inserted in 1/2 inch deep holes. The shelves will only be supported on the sides; not along the length. Should I worry about the sag of the plywood? What's a good length of the shelf that can sustain a load full of books without additional lengthwise support? Thanks! Vlad

[RonB]

Yes - you might sag, especially with books. Consider doing both of the following:

Upsize your shelf to 3/4 plywood - quite a bit stiffer

Trim the front with a piece of oak about 3/4" wide by 1" or 1-1/4" high. You can route or roll the edges for appearance. It will give you a little more edge stiffness.

[Rich B]

I would strongly second RonB's comments. A 36" wide shelf that's only 1/2" thick is bound to sag, especially if not supported along the length. Upgrade to 3/4" plywood at the very least. Wouldn't be surprised to see even the

3/4" sag if you don't use the oak/hardwood trim piece at the front edge of the shelf.

If you have access to it, Andy Rae's "The Complete Illustrated Guide to Furniture & Cabinet Construction" has lots of useful info relevant to what you're asking about.

[Lawrence Wasserman]

1/2" plywood will sag to much for a 35" wide shelf full of books. Unless you use 3/4" ply or add some kind of bracing or stiffener, you probably should keep the length around 12" or so for 1/2" plywood.

[Dean]

My son has a creative punker friend who is only 17, he made a set of (adjustable) shelves from 3/4 rough slabs and barb wire and nothing else. They are suspended from a ceiling beam. Ouch! They actually look pretty good.

[Bob Gramza]

[Vlad]

How about an inch wide strip of 3/4 ply supporting the shelves lengthwise both at the front and at the back of the shelf? Would this help? Vlad

[patrick conroy]

yes. 35" span with books and half-inch ply will most likely sag

Depends on the books. How many copies of Lehninger's Principles of Biochemistry are on them?

I rarely go over 32" with 3/4" plywood. Dunno for 1/2". (Even 32" and 3/4" will sag some, about 1/32nd to 1/16")

[Dean]

Why not a nice dadoed vertical strip up the middle front? Looks nice, less work.

[Phisherman]

A 35" span will require 3/4" ply, plus a 1.5" lip on the front to prevent sagging. Rabbet the lip and secure with carpenter's glue and biscuits or finishing nails. If you want super-strong shelves, put a lip on the back as well as the front. Half inch ply is just not practical for heavy loads.

[Wally Goffeney]

Your shelf will sag about 0.30 inch over a 35" length. Anything over .09" would be noticeable, according to the Sagulator:

'll do well to follow the many suggestions to upgrade the shelf thickness and add stiffener(s).