Granite surface plates are precision reference tools made from natural stone materials. They are widely used for the inspection of instruments, precision tools, and mechanical components, providing an ideal reference plane. Compared with traditional cast iron plates, granite plates offer unique advantages in high-accuracy measurement due to their excellent physical properties.
High-quality granite plates are manufactured from carefully selected natural stone. After mechanical cutting and precision hand lapping in a temperature-controlled environment, the surface plates achieve excellent flatness and dimensional stability. Their uniform texture, black glossy appearance, high hardness, and strong load resistance make them superior measuring bases.
Technical Requirements for Manufacturing Granite Surface Plates
Material Selection – Granite surface plates should be made of fine-grained, dense natural stone such as diabase, gabbro, or high-grade granite. The content of biotite must be less than 5%, elastic modulus higher than 0.6×10-4Kg/cm², and water absorption below 0.25%.
Surface Quality – The working surface must be uniform in color, without cracks, pits, loose structures, or other defects that may affect accuracy. Minor cosmetic imperfections that do not impact measurement precision are allowed. However, cracks or damaged edges on the working face are not permitted to be repaired.
Hardness & Precision – The working surface hardness should be greater than 70HS. Surface roughness (Ra) should be 0.32~0.63μm, while the sides should not exceed 10μm.
Flatness & Accuracy Standards – Granite plates are classified into Grade 000, 00, 0, and 1 according to accuracy levels. For Grade 000 and 00, handles should not be installed to avoid affecting accuracy. For Grade 0 and 1, threaded holes or slots may be added but must not exceed the working surface height.
Tolerance Requirements – The vertical tolerance between the working surface and side surfaces must comply with Grade 12 standards of GB/T1184.
Advantages in Use
Granite surface plates are more durable than cast iron or steel measuring bases. Even when impacted by heavy objects, only minor chipping may occur without compromising precision. Their stable accuracy and resistance to deformation make them indispensable in laboratories, machining workshops, and quality control facilities.
By ensuring proper material selection, precise machining, and correct usage, granite surface plates deliver long-lasting accuracy and reliability for precision measurement applications.