The surface quality of drillings can be further improved by either cutting the inside surface of the drill hole with reaming or honing, or by nonchipping smooth rolling. In reaming (also termed peeling), extremely fine chips are cut off using a cutter head with several adjustable knife edges, thus improving the desired dimensional and formal accuracy. Circularity errors and drift ridges can thereby be eliminated, especially frequently a requirement for hydraulic cylinders and pipes. In pipes, this also ensures the required hollow inner diameter, which is then inspected with a drift.Honing is a fine grinding process in which radially arranged honestones cut off a minimal amount of chips to further reduce surface roughness.
In rolling (smooth or surface rolling), the component surface is smoothed by plastic deformation with rolls or balls arranged coaxially to the drilling axis and, depending on the degree of forming, cold worked.
In smooth rolling, the surface is only smoothed to improve the bearing area, while in surface rolling the surface layer is further plastically deformed to achieve a residual compressive stress in the surface through cold working.
Turned Surfaces and Threads For especially stressed threads, rolling of the thread root (“cold working” as per API) can build up a residual compressive stress in the thread root, thereby reducing the sensitivity to fracture of components subjected to high stresses.Surfaces machined by turning can also, where required, be further improved by smooth or surface rolling. Here, rolls or balls are pressed against the surfaces with great force to plastically deform and, depending on the degree of forming, cold work them. A distinction is made here between smooth rolling, in which the surface is only smoothed to improve the load carrying surface, and surface rolling, in which the surface layer is further plastically deformed to achieve a residual compressive stress in the surface through cold working. This process is particularly suited to mating and bearing seat surfaces subject to high stresses.