The dovetail joint is a classic, beautiful, and strong method for connecting two pieces of stock. However, there are times where the dovetail wouldn't be the best choice.
For instance, what if you need to connect two pieces of plywood as opposed to hardwood? Using dovetails to connect plywood would considerably increase the chances of delaminating the plywood when testing the joint while dry fitting.
What if you didn't have access to a dovetail jig and a router? Or perhaps you didn't want to go to the trouble of hand-sawing dovetails? Is there another option other than dovetails to use in your woodworking projects?
Absolutely. A very simple alternative to the dovetail is called the box joint. As you can see from the image above, a box joint is very similar to a dovetail, with the difference being that the fingers in the box joint are rectangular rather than dovetail shaped.
There are a few ways to cut box joints. Of course, you could always do it with a dovetail saw and chisel. Simply pick a width for the fingers that will divide evenly into the width of the stock. In other words, if your stock is six inches wide, a half-inch wide finger would allow for twelve fingers total, six on each piece of stock.
Machining the Fingers
If you don't want to cut the fingers by hand, there are two ways to machine them. First, nearly all dovetail jigs can cut box joints. While you should check the documentation that accompanies your jig for the exact instructions, the setup is basically just like cutting the tails of a dovetail joint except that the bit would be a straight-cutting bit rather than a dovetail bit.
An even simpler method is to use a box joint jig on your table saw with a stacked dado set. Determine the width of each finger, then set up the stacked dado set to that width. Set the depth of cut to the same height as the thickness of the stock.
Next, attach a scrap piece of stock to your miter gauge. The scrap should be wide enough so that, when attached to the miter gauge, it extends past the blade by at least an inch and at least two inches past the miter gauge on the left side.
Verify that the miter gauge with the attached piece of scrap stock is square to the blade, and then run the scrap through the saw.
Next, remove the scrap from the gauge and move it to the right twice the width of the fingers, and re-attach to the miter gauge. For instance, if the fingers (and consequently the stacked dado set) are 1/2-inch wide, you should move the scrap one inch to the right and re-attach it to the miter gauge.
Now, cut a small piece of stock that is the same width as the fingers that will fit into the cut you made in the scrap. However, this piece should be at least twice as long as the width of the workpieces. Attach this piece in the notch in the scrap with a wood screw from the bottom, positioned so that it protrudes forward from the scrap toward the saw blade. This will act as a gauge for cutting the fingers.
Finally, verify that the miter is still square to the blade, and turn on the saw and cut a new notch in the scrap in its current position.
Cutting the Fingers
Now that you have the jig made, grab one of the workpieces and place it on end, firmly against the scrap and up against the little guide you attached to the notch in the scrap. Hold the stock tightly against the scrap piece and run it through the saw. Once it clears the blade, slide the entire assembly back through the blade, taking care to hold the workpiece tightly against the scrap. You have just cut the first finger and notch, precisely at the proper width.
Now, with the gauge and workpiece well clear of the blade, move the workpiece to the right and slip the newly cut notch over the little guide piece. Hold the stock firmly against the scrap and cut the next notch in the same manner as you cut the first.
Continue cutting notches until all of the fingers of the workpiece have been formed.
The opposing workpiece is cut in a similar manner, except that the first cut is not made with the stock up against the guide. Instead, the outside edge of this piece should be flush with the outside edge of the dado blade. This can be easily positioned by lining up the outside edge of the workpiece with the edge of the notch in the scrap. Once it is lined up, make the first cut, then proceed using the guide as noted above.
Once all of the fingers on both sides of the joint have been formed, be sure to dry fit the joint. However, if you have built the jig properly, the joints should be perfect every time.
To assemble, simply apply a thin layer of glue on all joint surfaces and slip the joint together and clamp as needed. This type of joinery works fine for making box-like structures such as drawers. However, you'll need to be a bit more diligent about keeping the box square when clamping than you might need to with dovetails.
Even so, the box joint is a relatively strong and useful joint, one that can be a lot of fun to build. It is not as elegant as dovetails, but certainly very appropriate in some circumstances.