Flat Precision High Granite Surface Table Grades 000
The grading system for granite surface plates is based on the
degree of flatness and tolerance that is accomplished. The American
Society of Mechanical Engineers (ASME) offers required
specifications that go beyond the quality of flatness in order to
standardize the use of granite surface plates. These additional
qualities include: support point location, surface finish, methods
of inspection, repeat measurement accuracy, material properties of
granites, and more. However, the three main grades for standard
granite surface plates follow the federal specifications for
flatness tolerance. Those grades are: Laboratory Grade AA which
means the plate has a flatness tolerance equal to (40 + diagonal
squared/25) x .000001″ (unilateral), Inspection Grade A which has a
flatness tolerance equal to Laboratory Grade AA times two, and Tool
Room Grade B which has a flatness tolerance equal to Laboratory
Grade AA times four.
(d is the length of the diagonal)
