The technical R&D teacher at my school asked this for an extra credit question on the Final. How fast is the edge of a router bit moving? Given a blade of diameter D inches, revolving at a rate of R rpm, a point on the perimeter of the blade will travel the length of the circumference C each revolution. Speed = distance / time C = pi x D pi ~= 3.1416 Speed: Distance/revolution x revolutions/time = C x R inches/minute What is the speed of a 1" router blade, moving at 20,000 rpm at the perimeter. Answer must be in miles per hour.