What level of roughness can be achieved with different machining methods?

As mentioned above, the maximum machining precision and corresponding roughness achievable with each machining method are determined by several factors, including equipment performance, material properties, tool quality, etc. Below are the approximate maximum machining precision and corresponding roughness ranges for these machining methods under general conditions:

T.V.Vorburger,J.Raja, SURFACE FINISH METROLOGY TUTORIAL.

Electric discharge machining: Precision 0.1-1μm, Ra 1-10μm. Precision grinding: Precision 0.01-0.1μm, Ra 0.05-0.25μm. Turning: Precision 0.1-1μm, Ra 0.25-0.5μm. Milling: Precision 0.1-1μm, Ra 1μm. Diamond machining: Turning precision 0.001-0.01mm. It is important to note that these values are estimates under general conditions. The specific machining precision and roughness also depend on factors such as specific processes, equipment, materials, etc. In actual production, to achieve higher machining precision and smaller roughness, more advanced equipment and precise processes are usually required, along with strict control of various machining parameters.
A schematic diagram illustrating improved surface roughness through polishing.
For example, precision polishing of ceramics and glass can achieve nanometer-level Ra roughness.

Ceramics:

Glass：