Shelving Fast Facts at left). This program considers the material, size and loading of a shelf and gives you a rough idea of how much a shelf will sag. So what if you find your shelf isn't up to the task?

Strengthening a Shelf. One of the simplest ways to minimize sag is to make shorter shelves or make them deeper. But that's not usually an option since it affects the overall design and look of a project that I may not want to change.

Giving Plywood an Edge. Instead, 1 look for ways to give my plywood an "edge." What do I mean by that? Well, I almost always have to cover up the edge of plywood with thin strips of hardwood to hide the plys, like you see in the top photo at right.

But hardwood edging doesn't always have to be thin and narrow. With a little thought and extra work, you can make that edging strip do so much more — it can really add strength to the shelf.

To do this, but still maintain the look of a "thin" shelf, I'll often use a wider hardwood strip. Gluing on a wider strip can be a challenge. So when I do this, I like to use a tongue and groove joint, like you see in the second photo from the top. The tongue and groove provides a mechanical "lock," so it's easy to keep the strip aligned with the face of the shelf. For many shelves, this simple addition may be all it takes to eliminate any noticeable sag.

Turn it on Edge. But the best way to ensure a strong shelf is to simply take that strip, widen it just a bit, and turn it on edge, like you see in the main photo on the opposite page. Now there are a couple ways you can add a strip on edge (see lower two photos at right).

The first way is to cut a rabbet in the hardwood strip and glue it in place. Tlie other is to join the edging to the vhelf with a tongue and groove joint. Both ways will triple the strength of a shelf. Even though the tongue and groove joint is a little more work, it ensures the edging and shelf are aligned perfectly without much effort.

Heavy-Duty Designs. There are tones when strength matters most. To see a couple different ways to make a really strong shelf, check out the box below. E3

How-To; Add Strength

Heavy Loads: Beefing it Up

Super-Strong Shelves. For very heavy loads, like encyclopedias and electronics, you might want to consider the shelves shown above. They add more strength than what's shown In the margin.

Adding a pair of strips under the shelf along with an edging strip (left) helps reduce the sag to a fourth of a plywood shelf the same size. Want a simpler look with less joinery/? You can get the same strength by doubling the thickness of the shelf and then gluing on a wide edging strip (right).

Simple Edging. Although it adds a small amount of strength, the main purpose of a strip of thin edging is to cover up the plywood edges

Wide Hardwood Strip. To add strength, but still maintain a "thin" edge, use a tongue and groove joint to add a wide hardwood strip to the shelf.

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