Tongue and dado joints are a strong way to join wood at ninety degree angles, such as for a drawer box, using only glue. I like the look of the joint and often use it on projects with visible joinery.

Having made these joints using both a tablesaw and hand-held router, I’ve found the tablesaw method to be less time consuming to do well.

Equipment

• Tablesaw
  • A dado blade of the exact dado thickness can help, but this tutorial explains how to get by without one.
• A sacrificial fence, such as a scrap piece of plywood
• Combination square to measure tablesaw blade height
• Wood glue
• A chisel to clean up incremental saw marks, if needed

Technique Overview

An inset groove, or dado, is cut into one of the joined workpieces using a tablesaw. The same saw is then used to cut a tongue on the other workpiece to fit into workpiece snugly.

Tutorial

When planning a project that will use this joint, consider how the project will be used & especially how gravity or other forces will act on the joints. Although wood glue is plenty strong on its own, I plan tongue & dado joints so that gravity acts perpendicular to the joint. For example, if building a box-shaped frame that will hang on a wall on its side, the gravity should pull weight down on joints that fit together sideways. This allows the strength of the wood to absorb the force alongside the glue, rather than glue alone in an up-down joint orientation.

This tutorial includes guidance to repeat steps for repeated joints in order to minimize calibration of the saw to achieve a consistent width and depth as much as possible.

1. Decide the width of the dado and tongue. When working with ¾” material, I find it easiest to choose ⅜” for both, mostly for fewer distinct measurements. The dado width & depth can be varied for visual effect, but this example will stick with ⅜” for both and assume ¾” material.
2. When preparing the boards to fit into this kind of joint, account for the width of the tongues after they fit into dados. For example, let’s say a 36” wide box is desired. If using butt joints, the width would either be the full 36” (if connecting pieces butt against the sides) or 34½” (if this piece butts up against a ¾” thick piece on each end). If this piece instead has tongues on either end, extend the latter measurement by the width of the tongues: 34½” + ⅜” * 2 = 35¼”.
3. Start by cutting the dados. If the project involves multiple joints of the same width and depth, cut all of the dados first to make them as consistent as possible.
   1. Set the tablesaw blade depth to just less than ⅜”. Run a piece of scrap through & measure the cut depth until dialed in just right.
   2. Set the fence position to ⅜” as well. This is the width of the gap between the dado and end of the board.
   3. This type of joint likely involves cross-cuts, which increase the risk of kickback. Use a cross-cut sled or carefully guide the workpiece through using a miter gauge. The key is to hold the workpiece securely perpendicular to the blade that it has no room to twist & potentially bind, leading to kickback.
   4. Pass all workpieces requiring dados through at ⅜”.
   5. Open the fence in slight 1⁄16” increments, and run each board through at each increment before increasing. Proceed toward the inside of the board until the dado is also ⅜” (it should take no more than 3-4 increments depending on the blade kerf). It’s important to pass all boards through before moving beyond the innermost or outermost increment for consistent dado width all around.
   6. Clean up the dados with a thin chisel if needed.
4. Next, cut the tongues. For this step, clamp a sacrificial fence so that the blade can spin as close as you can safely get it to the fence.
   1. With the blade up against the fence, set the blade depth just under ⅜” and make a cut on the first tongue workpiece
   2. Do a test fit into the end of the dado. It should be just a bit too wide, since the blade depth was started under. Adjust the blade height up to dial it in.
   3. Open the fence in slight 1⁄16” increments. As you approach ⅜”, begin test fitting for both depth and height.
   4. Unlike with the dados, I like to cut each tongue for the specific dado it will fit into, just in case there are slight variations in depth or width of the dado. So, repeat the previous two steps for each joint’s tongue.
5. Complete a test fit of all joints, then glue & clamp them.

If your saw is anything like mine, beware that the blade height crank can adjust slightly due to the kick of the saw turning on. Unlike the fence, it can’t be locked in (at least not on my saw). I try to remember the crank’s position once it’s dialed in & fine tune to that position immediately before each cut.