to rotate thereon the arched shaft is fixed with its arched portion downward then a cutting blade is applied to the roller surface layer in rotation so as to shape the desired profile of the roller surface layer that exhibits a top surface which is horizontal arched or convex in common with all the profiles the roller surface layer is cut so that the diameter thereof diminishes progressively toward the end portions in this way the profile of the roller is shaped as shown in fig2 a 1a or 3 as desired the important thing is that the arched roller is fixed with its arched portion downward in a vertical plane in which the shaft is projected from its side the shaft is arched to the extent which allows the roller surface layer to rotate thereon in general the curvature is 9 mm to 400 m preferably 18 mm to 200 m more preferably 36 mm to 100 m there is no limitation to the length and diameter of the shaft in general the length can be 8 mm to 20 m preferably 12 mm to 10 m more preferably 15 mm to 6 m and the diameter can be 1 mm to 5 m preferably 2 mm to.