How to build square joints

Sep 19, 2023

There's more than one way to build a wooden box.

By Jean Levasseur | Published Jul 26, 2023 8:00 AM EDT

In addition to properly milling up your lumber, knowing how to connect boards at crisp and strong 90-degree angles is one of the most important skills woodworking novices need to master. Luckily, there are a lot of different ways to do it.

As with so much in this craft, there’s not really one best way to join boards. The method you use will vary depending on variables like the tools you have available, your budget, how many of each type of joint you’re making, whether your project needs to look high-end, and, of course, what technique you think would be fun to work with on any given day.

Any of the following four joining techniques should be accessible to beginner woodworkers and provide good-quality joints that should last for years.

The simplest way to make a 90-degree joint is to screw from the outside face of one board into the connecting end of the other. As you usually do when using screws, you’ll need to pre-drill the holes to ensure that neither board splits.

If you choose this approach you might want to countersink the holes for the screw heads so that they sit below the surface of the wood. This will help hide the screw heads and prevent the hardware from splitting the board if you drive it all the way in. But countersinking can also prevent accidents by keeping your shirt from catching on one of the screws while you’re working or just innocently walking by.

If you don’t like the look of screws, you can cover them with wood putty or drill a countersink hole big enough so you can hide the screw head with a dowel. This can also be a design opportunity—by using contrasting wood for your dowels, you can add an interesting visual accent to your piece.

[Related: The surprising woodworking tools you already have around the house]

One of the drawbacks of only using screws to build squared joints is that all the pressure of the connection will be concentrated on the area right around the screws. This means the boards are more likely to break or crack in those particular places—especially if they’re thin. Screws can also loosen over time as the joint flexes with use and the wood’s natural expansion and contraction over seasons.

To make this joint stronger, you can add a bead of glue along the edge of one of the boards to help alleviate the strain. In this case, the glue will act as the main hold while the screws essentially serve as clamps until the adhesive dries.

If you don’t want to see any screws or patched holes, you can try pocket hole screws. This method will require a pocket hole jig, which is inexpensive and will allow you to drill faster and more accurately.

Using the jig, drill long, angled holes into the face of one board, pointing toward the edge. These holes hold the screws at an angle, letting them emerge from the edge and drive into the other board. As long as you plan your project carefully, you may be able to keep these holes hidden from view by placing them inside, underneath, or behind your finished piece. If you must drill a hole on a visible part of your project, or you just want to go for a polished no-holes look, you can plug them with pre-cut or standard dowels. Just keep in mind that a lot of the time these plugs will still be somewhat visible, so it’s better to plan ahead and keep them hidden whenever possible.

The pocket hole screws method suffers from the same limitation as the previous technique on this list—the breaking force is all focused in a very small area. But just like we mentioned above, a line of glue will help stabilize pocket-screwed boards over the long term.

Pocket hole screws and glue are how I built my very first piece of furniture, which is still as solid as the day I made it over ten years ago.

Using screws and glue to join wood is fine, but if you want more stability and durability, you can insert one board into another. This is where simple dados come into play.

A dado joint essentially consists of a channel cut into one board that is the same width as the connecting board, allowing the pieces to fit together tightly. As an added benefit, dados provide more surface area for glue to adhere to: along the three faces of the channel rather than only on the edge of each board. This makes the adhesive stronger and the wood less likely to crack.

You can make one of these joints by using a dado stack on your table saw. If you don’t have one of those, you can take multiple passes with a single blade, or use a router with a straight cut bit and a straightedge.

The last and most advanced technique on our list is using dowels, biscuits, or dominos. The idea is to drill matching holes on adjoining boards and glue a specifically shaped piece of wood into those holes to connect the boards.

The easiest and cheapest of these options is to use standard dowels and a doweling jig with your power drill. Mark out where you want the holes to be and use the guides on the jig to drill them out. Glue the dowel into place, smear some glue along the edges of the boards, and clamp them together until the glue is dry. This essentially creates a mortise and tenon joint, without having to actually cut a mortise and tenon, which is time-consuming and requires skill and practice. Like the dado, this method adds strength to the joint by providing mechanical support and increasing the glued surface area. As an added benefit, the fasteners are completely hidden inside the boards, creating smooth transitions.

[Related: Build your own router sled to flatten wood without buying big, expensive tools]

Biscuits and dominos are functionally the same in principle but use differently shaped pieces of wood. They also require specialized, more expensive tools. Biscuits, which are flat, thin, and generally oval-shaped slices of wood, tend to be more for alignment than adding much in the way of strength to a joint. Dominos, on the other hand, are like wide, flat dowels, and provide alignment as well as a great deal of shear strength.

If you’re an occasional user, a doweling jig works well and is the lowest-cost option—this is what I use. If you’re primarily interested in gluing up panels and keeping them flat while clamping, then a biscuit joiner is a great choice. If you eventually decide to make a lot of furniture with complex angles at the joints, then investing in a domino jointer machine might be worth the high price.

Jean Levasseur is a DIY contributor at Popular Science. He’s an avid woodworker and a stay-at-home parent of twin boys. When he’s not chasing the twins around the house or trying to fix or build something, Jean is a fiction writer, musician, and avid gamer.