Smoothing round internal passages of additively manufactured parts using metallic spheres

A method for smoothing surface roughness within an internal passageway, comprising:

• urging a first sphere into the internal passageway and to a first distance along a length of the internal passageway, wherein the first sphere has a first sphere diameter greater than or equal to a diameter of the internal passageway;
• and
• urging a second sphere into the internal passageway, the second sphere having a second sphere diameter greater than or equal to the diameter of the internal passageway, the second sphere urging the first sphere to a second distance along the length of the internal passageway,
• wherein an inner surface of the internal passageway is smoothed by the first sphere along the second distance of the length and wherein the inner surface of the internal passageway is further smoothed by the second sphere along the first distance of the length.