How to Cut Stair Shims

Lay the lumber you're using to create the shim face-up on a flat work surface. Stretch the tape measure out over the lumber from outside edge to outside edge. Make a mark on the lumber to indicate the shim width. Continue measuring across the entire butt end of the lumber to determine the shim measurements.

Hook the tape measure on the butt end of the lumber and stretch it out to the length of shim you need. Make a mark on the face of the lumber. Set the rafter angle square on top of the lumber. Flush the rafter angle square fence tight against the edge of the lumber and line the straight edge up with the mark. Scribe a line across the face of the lumber.

Flush the rafter angle square fence to the butt end of the lumber. Line the straight edge up with each mark you made and scribe a line along the length of the lumber to represent each shim.

Set the front end of a circular saw's cutting table on the end of the lumber. Line the blade up with the first scribed line and squeeze the saw's power trigger. Push the blade into the lumber following the first line and stop once you reach the line that represents the shim's length. Slide the saw back and continue cutting each line in the same fashion.

Cut the line that represents the shim length with the circular saw to separate the shims from the uncut lumber.