4.242 cm. According to the mathematical formula, it is known that the chamfer of c3 is 3×45 degrees, the right angle side is 3 cm, and the width of the hypotenuse is 3× 1.4 14 = 4.242 cm, so the chamfer of c3 should be 4.242 cm. Chamfering refers to the process of cutting the edges and corners of the workpiece into a certain inclined plane.