Two hackers from North Carolina have developed a process that smooths the striations on 3D printed objects. It replaces them with a delightful shiny surface.
Austin Wilson and Neil Underwood take advantage of the fact that ABS plastic--one of the common materials used by 3D printers--is soluble in acetone. To smooth their models, they place a jar with the model and a small amount of acetone on a hotplate. When they apply heat to the jar, the acetone evaporates and slowly melts the surface of the model. As the acetone dries, the plastic hardens and the model can be handled and painted, just like any other ABS part. This is much easier than the methods I've used to fill or smooth
While the tools required are inexpensive, you do need to be careful. As anyone who has cleaned glassware in chemistry lab knows, acetone isn't particularly harmful, but it is extremely flammable. That said, the results in the pictures posted by Wilson and Underwood are good enough that I'm looking for my hotplate.