Cutting angles on a mitre saw is called "mitring" the board or piece trim. When you mitre a board, the total angle measurement that two boards placed together will create is divided evenly between the two boards. Therefore, when you need a 90-degree angle, you will cut each board at a 45-degree angle. When the boards are joined together, they will form a 90-degree angle. Cutting large angle on a mitre saw is a simple matter of measuring the total angle to be created, and then cutting 1/2 of the angle on each board.
If you are making a picture frame or another decorative trim shape that forms a complete geometric figure, such as a square, determine the number of mitre joints--or angles--in the figure, and divide that number into 360. (The total degrees completed by all the mitre joints add up to 360.) For example, in a rectangle with 4 mitre joints, each mitre joint has 90 degrees. In a hexagon with 6 mitre joints, each mitre joint has 60 degrees. For other shapes, use the protractor or carpenter's bevel to determine the correct angle.
Divide the angle of each mitre joint by two. This final number is the angle to cut on each end of each board.
Set the mitre saw to the appropriate angle. Carefully measure the board to the needed length.
Place the board on the cutting table, pressed against the metal wall along the back of the tool table area. Cut the board by slowly bringing the mitre saw down on the board. Repeat the process on each end of each board.
Calculating the angle of cuts for large mitre joints can be confusing. Large angles, also called obtuse angles, are measured along the outer edge of a mitre joint. For example, cutting a 30-degree angle on two pieces of trim forms a 60-degree angle. The path of board changes direction by 60-degrees. However, when the resulting angle formed by the joined wood pieces is measured, the result is a 120-degree angle. Thus by cutting small angles on the mitre saw, a large angle is formed between the two pieces of joined wood.