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.
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.