3 Plenty-strong plywood joints
1. Full-width dado or groove
Strong, reliable, and easy to make, a full-width dado (across the grain) or groove (along the grain) perfectly captures the mating workpiece with glue surface all around. As a general guideline, cut a dado to a depth about half the thickness of the plywood. A cabinet, bookcase, or dresser built with snug-fitting, glued-together dado joints will last for decades.
You can cut dadoes and grooves with a tablesaw or router. We like using a stacked dado set on a tablesaw because it's quick and easily repeatable.
Stack the right combination of chippers, shims, and outer blades, shown right, to match the plywood thickness, and install that setup on your tablesaw. Make test cuts in scrap until you get the right fit -- the inserted workpiece should slide in and out of the dado with moderate hand pressure but not fall out when held upside down. Add or remove shims as needed.
Once you get your stack set up, you can cut all your dadoes for stock of that thickness. Registering against the rip fence, as shown below right, guarantees that all cuts made on matching workpieces will be perfectly aligned.
For corner joints, this channel becomes a rabbet. Because you lose one of the glue surfaces of a dado, it's best to use a rabbet in conjunction with an additional form of support, such as screws or a solid-wood face frame covering the exposed edges.
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