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How to Make a Half-Lap Joint

Mill your own half-lap joint quickly and easily using nothing more than a portable circular saw and a chisel.

Half-lap joints are commonly used when building with framing lumber, especially on long runs and for 90-degree intersections. They keep the mating surfaces flush and the wood thickness uniform. Although there are several ways to cut a half-lap, here’s how to quickly mill one using nothing more than a portable circular saw and a chisel.

Cut A Series OF Saw Kerfs Across Boards To Make Half-Lap Joint
Cut a series of closely spaced saw kerfs across the boards.
Illustration by Narda Lebo

Steps on Making a Half-Lap Joint

1. Clamp two boards side by side with their ends even.

  • Measure a distance in from the ends that’s equal to the width of one board, and mark a square line across both boards.
  • Set the depth of cut on the saw to half the thickness of the boards and make a cut along the line to form the shoulder of the joint.
Chisel Away Waste Wood To Make Half-Lap Joint
Use a chisel to clear away the waste wood.
Illustration by Narda Lebo

2. Next, cut a series of closely spaced saw kerfs across the boards.

  • Use a chisel to clear away the waste wood and smooth out the broad, flat surface of the joint.
  • Unclamp the boards and put them together cheek to cheek to form a 90-degree angle.

3. Then assemble the joint.

  • The method of assembly depends on the thickness of the boards and the size of the completed frame. Typically, frames built with 2-by lumber or thicker require mechanical fasteners.