Even if you have mastered the art of cutting trim around the baseboards of rooms and entryways, the problem of cutting trim molding for stairs can often puzzle the do-it-yourself carpenter. The angles created by the flat stair landings and the rising stair stringers can make it difficult to determine the proper cutting angle for a joint between two sections of trim molding. Fortunately, you can easily determine this cutting angle yourself, even without an advanced degree in geometry.
Put on a pair of safety glasses, and cut a scrap piece of stair trim molding, of the same type that you plan to install. The scrap piece should be about 1 foot long. Cut the scrap piece at a simple 90-degree angle.
Set the scrap piece of stair trim molding on the flat stair landing, in the position it would be if it were installed. Slide the trim along the landing until it overlaps with the position that would be occupied by the adjoining piece of trim. Trace along the top of the trim on the wall with a sharp pencil.
Position the scrap piece of trim molding on the rising stair stringer. Slide the molding along the stringer until the top of the molding intersects with the line you just drew on the wall. Trace along the top of the molding with a sharp pencil, so that the two pencil lines intersect.
Use a ruler to connect the intersection point you have just drawn with the point where the rising stair stringer meets the flat stair landing. Connect the two points with a sharp pencil. This line is the template for the cuts you need to make in the trim molding.
Hold a piece of trim molding in place along the rising stair stringer or the stair landing. Slide the molding until it overlaps with your wall template. Make a pencil mark at the top and bottom of the molding, in line with the top and bottom points of your template.
Cut your trim molding along the line between the two marks, and test the resulting cut against your wall template.