Surface plate

[3] Joseph Whitworth, born in 1803, had been an apprentice with Maudslay from 1825 but had left by the time he started his own business in 1833.

GGG-P-463B was later revised and reissued on 12 September 1973 as GGG-P-463C, which provided common language and terms of classification for surface plate manufacturing and commerce.

On 15 June 1977 an amendment was issued to the federal specification in order to include requirements in metric units.

The American Society of Mechanical Engineers (ASME) decided to form a committee to revise the federal specification in accordance with modern technologies.

ASME also recognised the need for updates to incorporate modern concepts such as traceability and measurement uncertainty that have undergone considerable development since 1973.

The cast iron was aged to reduce stress in the metal in an effort to decrease the likelihood of the plate twisting or warping over time.

Despite a fall in popularity among machine shops, cast iron remains the most popular material for master surfaces (different use from a surface plates) among laboratory metrologists, machine builders, gauge makers, and other high-accuracy industries that have a requirement for gauging flatness.

Despite its high stability, cast iron remains unsuitable for use as a normal surface plate in high-tolerance production applications because of thermal expansion.

The nature and use of a master surface, by contrast, already necessitates expensive measures to control temperature regardless of material choice, and cast iron becomes preferable.

Glass can be suitably ground and has the benefit that it chips rather than raising a burr, which is a problem when using gray cast iron.

Granite surface plate calibration should be performed routinely to maintain proper flatness and ensure measurement accuracy over time.