I polished the ID with 8 inch long by 3/4 inch wide Sanding Cloth Strips wrapped around a 1/8 inch brass shaft about 2 inches long in the Dremel. The high air flow produced by the single flap wheel allowed the ABS to sand to a fine white powder instead of melting to black furry balls. Worked 'Great. There is a nice smooth S bend in this runner.
John