Lapping as a process is surface treatment using free abrasives. In engineering, this method is the slowest one, but also the most accurate machining method. The lapping process can be used not only for flat surfaces, which are the most common (for example, in the production of various seals, where high demands on flatness are needed. Here is possible to reach the flatness of around 1 micron), but also for spherical surfaces, or in the production of spherical inserts. Also is possible to lap pairs of tools working together so that their common surfaces are as compatible as possible. Various shaped surfaces can be also lapped, where in such cases over a larger shaped surface is moving smaller lapping tool. A wide variety of materials can be lapped: various types of steel, up to highly hardened, sintered carbides, glass, etc. Because of bland material removal during lapping, the process itself takes some time. To speed up the lapping process is necessary to use optimal procedures, abrasives, and lapping tools.
To achieve optimal surface quality in possible shortest time, is necessary to work many times in several steps. By working with abrasives with larger grain sizes, more material is removed from the lapped surface. By switching to a smaller grain size you can achieve a better surface roughness (given for example with the Ra value). Sometimes after the lapping process is followed the polishing process, where the roughness of the surface is no longer improved, but on the surface with the good Ra only the gloss of the surface is enhanced.