Holes making process is widely applied in die steel machining, Helical milling a hole, also called orbital drill, is hole making process by milling in which the center of end mill orbits around the center of the hole while spinning on its axis and moving in the axial direction. The paper presents the secondary regression prediction model of the holes surface roughness for helical milling of die-steel. To minimize the number of experiments for the design parameters, response surface methodology (RSM) with orthogonal rotatable central composite design is used. By means of variance analyses and additional cutting experiments, the adequacy of this model is confirmed. The model will be helpful in selecting cutting conditions to meet surface finish requirements in helical milling operation.