A cast iron surface plate is a large, flat, and smooth plate made of cast iron that is used as a reference surface for measuring the flatness and straightness of other surfaces. It is an important tool in manufacturing, engineering, and metrology, where precise and accurate measurements are critical.
Cast iron surface plates are preferred over other materials such as granite or steel due to their superior stability and resistance to thermal expansion. They are made by casting molten iron into a flat mold, which is then machined and finished to provide a smooth and accurate surface.
The surface of the cast iron plate is typically ground and lapped to a high degree of flatness and surface finish, often using a diamond or abrasive wheel. This creates a highly accurate reference surface that can be used for precision measurements and inspections.