Surface plate is made of ____.

Explanation:

Surface plates:

• When accurate dimensional features are to be marked, it is essential to have a datum plane with a perfectly flat surface.
• Marking using datum surfaces that are not perfectly flat will result in dimensional inaccuracies.
• The most widely used datum surfaces in machine shop work are the surface plates and marking tables.
• Surface plates are generally made of good quality cast iron which is stress-relieved to prevent distortion.
• The work surface is machined and scraped.
• The underside is heavily ribbed to provide rigidity.
• For the purpose of steadiness and convenience in leveling, a three-point suspension is given.
• Smaller surface plates are placed on benches while larger surface plates are placed on stands.
• Granite is also used for manufacturing surface plates.
• Granite is a dense and stable material.
• Surface plates made of granite retain their accuracy, even if the surface is scratched.
• Burrs are not formed on these surfaces.
• Cast iron surface plates are designated by their length, breadth, grade, and the Indian Standard number.