Surface Plate

Surface Plate is extremely important tool for layout operation. It gives an accurate reference plane. The reference plane is that plane through which measurements may be made for both layout and inspection. A surface plate may be employed for large amount of work. The surface plate employed for large work is known as layout table. Surface plate should be covered while it is not in use and kept clean while it is in use. Further, it should never be blown through hammer. This will influence the accuracy of the reference surface. Surface plate may be made up of cast iron or granite. Surface plate of cast iron is displayed in below diagram. Cast iron based surface plate is made from good quality casting. While the working surface of the casting has been finished to preferred degree of flatness, the distortion will be decreased by the age hardening.

Then casting has been permitted to age hardened to relieve internal stresses. The ribs are given on underside of the surface plate for rigidity. The large cast iron plate is mounted on a heavy stand or legs with provision for levelling. The plate is levelled periodically to make sure that the working surface of it is remains flat.

Figure: Surface Plate

Granite is superior to cast iron like granite is harder, denser and as well gives resistance to water. The surrounding flat surface will not get influences, if it is chipped. Because of such excellent properties, granite is frequently used now-a-days. As well granite is aged in the earth for long time that results in relieving of internal stresses in earth itself. The temperature withstanding capacity of granite is as well much more than other material.