Surface plates are flat, precision surfaces used as a horizontal reference for dimensional measurements. They serve as a foundational base for inspection, toolmaking, gauging, spotting, marking, and layout tasks. Common materials for surface plates include granite, metal, cast iron, and glass.
As benchmarks for measurement accuracy, surface plates play a crucial role in quality control. Their surfaces are manufactured to be extremely flat, with accuracy classifications ranging from Grade-00 to Grade-3. These plates are essential in machine shops, precision manufacturing, and industries like defense, automotive, and aerospace, where tight tolerances are critical. They are commonly used to detect inaccuracies or warping in manufactured parts.
For optimal performance, surface plates should be calibrated regularly—ideally every six months, though once or twice a year is the minimum. Frequent calibration is particularly important in areas that see heavy use, as it helps detect issues such as chipping, warping, or wear. An uneven surface can compromise the accuracy of measurements, leading to errors and the potential for defective parts to pass inspection.
To ensure an ideal surface plate, the material must meet the following key requirements:
- High rigidity to maintain its flatness
- Resistance to wear and corrosion
- Stability against warping and twisting
- Cast Iron (C.I.)
- Granite
- Glass
Cast Iron is the most commonly used material in manufacturing, machine shops, and shop floor as it provides the best surface plates over the other materials. and hard annealed in order to relieve internal stresses. Surface plates made from cast iron (C.I.) undergo heat treatment to relieve internal stresses. The top surface is precision-machined to achieve absolute flatness. The underside features a cored and ribbed structure, enhancing structural rigidity to support heavy loads.
Granite surface plates are highly valued for their resistance to rust. They are also less affected by temperature changes and heat, which allows them to maintain their flatness over longer periods. Additionally, granite is harder than cast iron, making these plates more durable.
Apparently, surface plates can also be made up of Glass. The main reasons to make the surface plates from the glass are due to the following reasons.
- Less Weight
- Free from corrosion and burrs
- Achieve high accuracy and it can maintain for longer life
But they need to be handled carefully they can be broken. Ceramic Surface plates are slowly replacing the glass.
- Regularly check the flatness accuracy of the surface plate to ensure it remains in ideal condition.
- Clean the top surface thoroughly before use to prevent dust and contaminants from affecting measurements.
- Cover the plate with a protective rexine or wooden cover when not in use.
- Use the entire surface, including the edges and corners, to ensure even wear and maintain uniform flatness.
- After use, coat the top surface with corrosion-resistant substances like oil or grease to prevent rust.
Surface plates provide a highly accurate, wear-resistant flat surface. In the case of granite plates, their low thermal coefficient of expansion ensures that flatness is maintained even during temperature changes. They are used for precise height measurements and accurate surface marking.