These plates are of close grained cast iron. They are amply ribbed to minimize deflection under load. The composition of the metal, the depth and cross-section of the ribs and the thickness of the plate are designed to conform to the deflection limits specified in IS 2285 -1963.

Surface plates are manufactured to two tolerance standards. - Grade-I and Grade-II. Grade-I plates are more precise than Grade-II plates. The deviation in flatness for Grade-I and  Grade -II  plates for sizes upto and including 2000 x 1000 mm are as prescribed in IS 2285-1963.

Grade-1 plates are artificially seasoned.They are hand scraped to achieve maximum local deviation from flatness of 5 microns over any length of 300 mm at any points on the working face , in plates of  630 X 400 mm and larger. Aspecial scraping technique is used to achieve a uniform distribution of load bearing points and oil pockets. An average of 15-20 load bearing points , after finish scraping , is standard. This finish scraping technique ensures that the area of the load bearing points increases  after the intial dulling of the high points. This guarantees a long working life, at the required accuracies.

These plates are of close grained cast iron. They are amply ribbed to minimize deflection under load. The composition of the metal, the depth and cross-section of the ribs and the thickness of the plate are designed to conform to the deflection limits specified in IS 2285 -1963.

Surface plates are manufactured to two tolerance standards. - Grade-I and Grade-II. Grade-I plates are more precise than Grade-II plates. The deviation in flatness for Grade-I and  Grade -II  plates for sizes upto and including 2000 x 1000 mm are as prescribed in IS 2285-1963.

Grade-1 plates are artificially seasoned.They are hand scraped to achieve maximum local deviation from flatness of 5 microns over any length of 300 mm at any points on the working face , in plates of  630 X 400 mm and larger. Aspecial scraping technique is used to achieve a uniform distribution of load bearing points and oil pockets. An average of 15-20 load bearing points , after finish scraping , is standard. This finish scraping technique ensures that the area of the load bearing points increases  after the intial dulling of the high points. This guarantees a long working life, at the required accuracies.