In this article two complementary methods are developed. Firstly, a method to add precision in large machine tools with modular lightweight structures (APLM), which performs the compensation of geometrics and dynamics errors using embedded intelligence, and secondly, an alternative polishing method called selective polishing (SP). This systematic process comprehends measurement tools and algorithm resources. Phenomena occurred in the machine structure, due to interaction between the cutting tools and the petrous materials in the grinding and polishing processes are modeled mathematically. Using validated flatness models, the variables and parameters were discretized to determine the errors with respect to the Z axis. To validate the method, a test machine of 3m 2 workspace with a multi-body lightweight structure design was built. The geometrical errors were determined using precision instruments and those were compared with a pattern surface. A higher flatness is achieved through a combined grinding-traditional polishing and selective polishing process using the same machine. This method saves time and energy consumption.