How to Calculate Compound Miter Saw Settings Using the Miter Angle and the Bevel Angle

1. Determine the number of sides the whole workpiece has. For example, assume you want to create crown molding for a hexagonal room. You need to know your flat miter cut angle, or the deviation from a perpendicular cut; the easiest way to calculate it is to divide 180 by the number of sides the room has. In a six-sided room, the flat miter angle is 30 degrees. Label this as 'A.'

2. Determine the bevel angle, the angle at which the piece deviates from a horizontal plane. Assume, for example, that you want your crown molding to form a 30-degree angle with the ceiling. Label this bevel angle as 'B.'

3. Plug A and B into the formula 'arctan(tan(A) * cos(B).' Doing this gives you 'arctan(tan(30) * cos(30).' Arctan is the inverse of a tangent, or 'tan-1' on a calculator. If you entered the formula correctly, you should get 26.565 degrees as the miter angle.

4. Plug A and B into the formula 'arcsin(sin(A) * sin(B).' Like arctan, arcsin is the inverse of the sine function, or 'sin-1.' You should get 14.478 degrees as the bevel angle.