In a recent article on these pages, we asked the question: How many corner joint methods are there? We wrote about two of them in that piece, the box joint, and the dovetail joint. But we only discussed the joinery and not the pieces being joined.
In this piece, we want to talk about using dovetails in plywood, as in making a plywood drawer, and whether that’s a good joinery choice for that material.
We know what plywood is, and you’ve most likely used it in a project or two in your woodworking shop.
It’s a manufactured wood product composed of thin layers (plies) of wood veneer. These plies are glued together, and during assembly, each ply is rotated 90 degrees from the previous ply. This rotates the grains of the plies, with each layer at 90 degrees against the previous ply.
Rotating the grains like this:
- Prevents splitting when nailed or screwed
- Reducing expansion and contraction as a result of changes in its environment
- Providing greater strength consistently in all directions across the plywood sheets
The various types of plywood generally refer to the number of plies in the sheet, most often in odd numbers, from 3-ply (the most common) to 5-ply to multi-ply. The 3-ply sheets run about 2 – 3 mm thick and are most often used for indoor projects because they appear more decorative than the thicker ply sheets, which can appear heavy and clunky rather than fine.
Plywood is real wood, though. Veneers of wood are glued together with a resin to form sheets which usually are 4 x 8 in size. The benefits of plywood include stability, a very positive strength-to-weight ratio, and resistance to chemicals.
Plywood Grades and Features
There are 5 grades of plywood, ranging from blemish-free and fully sanded, to partially blemished but repaired and sanded, to unsanded and blemishes apparent, and so on, with each successive grade likely to have voids on the inner plies.
For a drawer project, you are likely to be working with the highest grade, meaning the appearance will be blemish-free and fully sanded top and bottom layers. It may also be Baltic birch, which is at the top of the grade scale for appearance and durability. Baltic birch plywood will be pricier than any others, and there is a premium for the highest plywood grade.
Dovetail Joints in General
If you haven’t made a dovetail joint, it’s likely you have at least seen one. They are distinct, very professional-looking, and give a clean and polished appearance to a kitchen drawer.
They have trapezoidal profile cuts that will slide together to join two pieces of wood, or for our purposes today, plywood, at a 90-degree angle. Those profile cuts give the appearance of a dove’s tail, and that is where the name comes from. They’re common in furniture-making and are considered to be among the strongest of joints.
Dovetail joints require very precise cuts in the wood with a finish-blade hand saw and chisel. If not properly made, the joint will be weak and will likely fail. No mechanical fasteners are needed to strengthen them like other joinery methods do – like pocket hole joinery, for instance. Their pin-and-tail interlocking dynamic, where the pin of one piece will lock into the tail of another (and a little glue), will create a snug fit and a tight hold, one piece to the other.
It’s one of the most difficult joints to make, too. As we said, precision cuts are necessary to create that strong joint. Dovetails can be cut with a router and a dovetail jig, but for smaller pins, a hand saw and chisel or knife are the common tools required for the necessary precision.
Before the joints are glued and finished, it is common practice, and very important, to dry-test the joint. Lock the pins and tails together to ensure everything fits tightly and well; then carefully separate the pieces and move on to the glue-up and finish steps.
This is where it becomes a bit questionable when you are using plywood instead of solid wood.
The Risk of Tear Out in Plywood
Dry-fitting a dovetail joint is necessary to test the precision of the cuts. The pins and tails must fit together snugly for the joint to have strength. Gluing won’t make up for a bad cut and a loose fit when interlocking the pins and tails.
Once the testing has determined the cuts to be sufficiently precise, though, the pieces need to be separated for the gluing and re-integrating the pins and tails into that snug dovetail joint. This is where some “ifs” come into play.
- If you’re working with the highest grade plywood, and . . .
- If you’re working with Baltic birch plywood, the best to work with for any purpose when the project will be visible . . .
You may be safe. By safe, we mean you’re less likely to have plywood with voids in its interior, voids that could lead to some tear-out when knocking the pieces apart after a dry test. Even in the absence of interior voids, and even though the resin used in the manufacturing of plywood is very strong, there is still the risk of some loosening of the plywood or chipping of the pins.
This would adversely affect both the strength and the appearance of the joint. We’re making drawers, so the joints are likely to be seen. We’d want the dovetail joints to really be the star of the drawers – precision cuts, well-assembled, and very professional in appearance.
Box Joints As An Alternative
Box joints are another basic method of corner joinery with great strength. Offset profiles are cut in the two pieces being joined together, and these “pins” created are simply slid and interlocked with the offset slot in the other piece. The cuts are straight and parallel, so it is just lining them up and sliding the pieces directly into each other.
Box joints, also referred to as finger joints, can be interlocked from any direction, whereas the dovetail joint can be interlocked in just one way, the way that locks the pins and tails together. Dry-testing a box joint is easy, sliding the “pins” into the cuts from any direction and then sliding them out after testing.
The “pins” of a box joint also present a greater gluing surface, which will add strength and durability to the joint. The appearance of a box joint is both professional and aesthetically pleasing.
Because a box joint does not need to be knocked apart after a dry test, there is virtually no chance of any tear-out or chipping the pins. Thus, it is a safer joinery choice for drawers than dovetail joints – when working with plywood.
However, if you are working with solid wood, either joinery method will serve you well for all of the same reasons – professional and aesthetically pleasing appearance. Either joint can be enhanced in appearance if you use two different woods of different colors or tones.
Here’s a video that demonstrates the relative strength of a dovetail joint with plywood. Unfortunately, we could not find a video that presented any damage from a dry test of a dovetail joint. This video, though, is interesting in the testing of various joinery methods to withstand weight and shear.
The answer to the question is yes, you can make dovetail joints with plywood, but we offer a few caveats for you to consider, as well as an alternative that avoids the risk when working with plywood.