Dovetail Bits

 

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For centuries, the hand-cut dovetail joint has stood as a testament to the quality of the case, box, or drawer that beheld it. These days, thanks to routers and dovetail bits, even a beginning woodworker can incorporate this joint to enhance the simplest projects.

Dovetail bits come in an array of cutting angles—usually 7-14° —and heights (see photo, right), on both 1/2" and 1/4" shanks. Generally speaking, the greater the cutting angle, the stronger the joint. But beware: The acute angles on the tails make them more fragile as the cutting angle increases, and they can break more easily along the grain.

Because of its opposing-wedge action, a properly fitted dovetail joint self-tightens. This means you can use it to eliminate fasteners, such as screws or nails. You should still glue the joint, but you won't need clamps.

 

How to tell your pins from your tails

You'll see the three basic parts of every dovetail joint in the Parts of a Dovetail Joint drawing at right. The pin is the part that fits into the socket, which is formed by two tails. Pins and tails are often confused, but there's an easy way to remember which is which. If you look at the face of the workpiece and see birdtail-shaped protrusions, those are tails; if you see rectangles, you're looking at pins.

The tails bear the brunt of the joint's stress, so when planning your project, point the tails in the direction of the stress. For example, opening and closing a drawer creates front-to-rear stress on the drawer. Therefore, point the tails front and rear, which means cutting the sockets in the drawer sides.

 

Here in the WOOD® magazine shop, we like to cut the sockets first, about 1/32" deeper than the thickness of the pins, using a dovetail bit in our router table. Then, using a straight bit, we form the pins, leaving them just a hair wider than the sockets. This lets us gradually remove more stock from the pins until we get a good fit. Once the joint is complete, we sand the tails flush with the pins.

Making well-fitting dovetail joints in boxes or drawers requires a high degree of precision. That's why you'll find a covey of commercial jigs on the market today, each designed to simplify cutting the pins and sockets with bearing-guided bits. Less-expensive jigs make only half-blind joints, where the dovetails are visible only from one side of the joint. With pricier models, you can cut through-dovetails, where both sides show (see Common Corner Joints drawing, right).

Complete Guide to Mastering Your Router

 

 

Beyond the box: Let It Slide

Even without the use of expensive jigs, you can use dovetail bits to make other strong and attractive joints. For example, use a long dovetail slot (socket) inside a bookcase or entertainment center, then machine a long tail on each end of a shelf, as shown right. The resulting joint, besides adding beauty to the case, also keeps the case sides from bowing. And, if you don't glue the shelf in place, you can remove or replace it at any time.

Or, use a sliding dovetail joint instead of a stub tenon for making rail and stile panels, as shown below right You'll still want to glue the joint, but again, you won't need clamps for this assembly. Just be sure your panels are in place prior to gluing the frame.

One tip for cutting sliding dovetails: The tapered sides of the dovetail slot tend to trap chips in the slot as you cut. So precut the slot with your tablesaw, or a router and a straight bit, as shown below, to remove as much material as you can before routing the dovetail. If pre-cutting proves impractical, proceed slowly with the dovetail bit, backing it completely out of the cut frequently to clear chips and debris from the slot.

 

A Couple More Key Uses

As you can see from the drawing right, dovetail keys add decoration and function to any number of joints. The key is an hourglass-shaped piece of stock, often made from a contrasting species, that creates a mechanical joint between two flat surfaces.

Before cutting the key sockets, mill a long key blank using the same dovetail bit. Then, set up the socket cuts in scrap to ensure a good fit. Slice individual keys from the blank (about 1/32" longer than the socket), assemble the joint, tap the keys into place, then sand them flush with the workpiece.