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How to Splice Lumber

Nathan Fisher

Spanning long sections or working around corners on a construction project often requires splicing pieces of lumber. From making picture frames to connecting ridge poles, one of the simplest and most functional ways of splicing lumber is with a half-lap joint. Half-lap joints are fairly quick to make and can be cut in a shop or onsite with a variety of tools from a hammer and chisel to a table saw with jigs.

Lap joints are a common and simple method of splicing two pieces of lumber.
  1. Lay the two pieces of lumber to be spliced side by side. Push the boards together so the boards are making contact on their inside edges. Line the boards up so the boards are even on one end.

  2. Mark an "O" on the ends of both boards and an "X" on the top of both boards with a pencil.

  3. Measure the halfway point, up from the bottom, on the end of the boards with the ruler of the builder's square. If one piece of lumber is thinner than the other, measure the halfway point on the thinner piece. Draw a line with a pencil width-wise across the ends of both boards even with the mark.

  4. Flip the boards up on their sides so the "X" on both boards is facing outwards. Align the ends of the boards marked with the "O" so the ends are even with each other.

  5. Determine how long you wish the joint to extend, or overlap. Measure off the distance of the joint with the tape measure from the ends of the boards marked with the "O". Mark the point on both boards with a dashed line.

  6. Align the ruler of the builder's square on the dashed lines and draw a straight line across the sides of both boards, connecting the dashes.

  7. Separate the boards. Working with one board at a time, set one arm of the builder's square to align with the solid line going down the side of the board. Hold the ruler of the square even with the mark across the end of the board marked with the "O."

  8. Trace an L-shaped line along the inside of the square, down from the top of the board marked with the "X" and along the side of the board to the end marked with the "O." Repeat the L-shaped line on the second board.

  9. Put on safety glasses and cut along the L-shaped lines on both boards with a jigsaw. Line the overlapping pieces up to check for fit. For finish work, sand the cut smooth with sandpaper

  10. Apply a wood epoxy to all contact surfaces. Align the joints and clamp the boards together. Allow the epoxy to dry per the product directions.