Abstract: Aspects of the present disclosure are presented for techniques in removing roughness and surface anomalies in structures with internal passages and intricate external surfaces, such as structures with internal fluid passages constructed by additive manufacturing (AM), using an abrasive slurry. Post processing methods which are capable of smoothing non-uniform surface roughness within intricate fluid passages are a prerequisite to the widespread adoption of AM for complex fluid systems. In some embodiments, a mixture of abrasive powder and deionized (DI) water is used to create a viscous slurry which can then be pumped through the internal fluid passages of a workpiece until the desired surface roughness is achieved. This abrasive flow machine (AFM) is capable of smoothing a wide range of roughnesses, internal geometries, and printable materials.