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?
Yes - you might sag, especially with books. Consider doing both of the
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.
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
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.
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.
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.
: 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?
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")
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.
Your shelf will sag about 0.30 inch over a 35" length. Anything over
.09" would be noticeable, according to the Sagulator:
You'll do well to follow the many suggestions to upgrade the shelf
thickness and add stiffener(s).
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