Step 1
Measure the width of your bullnose stair trim. This trim is usually 1 1/4 inches wide.
Step 2
Line up your combination square for a 45-degree miter cut on the front corner of the side of the tread that will be exposed. The return may be on the right edge of the tread, the left edge or both -- called a double return -- if the stairway is open on both sides. Mark the corner for a 45-degree cut that's as long as the bullnose stair trim is wide.
Step 3
Unplug your table saw. Install a fresh blade intended for cross cutting wood, according to the manufacturer's guidelines. Plug the saw back in. Put on safety glasses.
Step 4
Make the 45-degree, 1 1/4-inch cut with the table saw. Remove the tread. There should be a 1 1/4-inch diagonal slice in the appropriate front corner of the tread.
Step 5
Mark 1 1/4 inches from the edge of the tread along the same side, using the ruler on the combination square as a guide.
Step 6
Run the tread through the tablesaw at the 1 1/4-inch mark, from the end opposite the miter cut until you reach the bottom of the mitered cut. Do not cut too far to avoid cutting into the miter.
Step 7
Finish the cut with a handsaw to remove any excess between the cross cut and the mitered cut.
Step 8
Mark and cut the bullnose stair trim with a 45-degree miter cut that lines up with the cut in the tread. The back end of the trim should extend just beyond the face of the stair riser that butts up against the tread. The back end of the trim, opposite the miter cut, can be routed with a bullnose router bit to give it a finished edge.