Granite Surface Plates

Surface plates (Fig. 3.7) are smaller reference surfaces and are placed on a bench for use with smaller workpieces. For general use, both surface tables and surface plates are made from cast iron machined to various grades of accuracy. For high-accuracy inspection work and for use in standards rooms, surface tables and plates made from granite are available. 

The plates may be made from good-quality close-grained plain or alloy cast iron, sound and free from blowholes and porosity, and must have adequate ribbing on the underside to resist deflection. Alternatively, plates may be made of close-grained granite of uniform texture, free from defects and of sufficient thickness to resist deflection. The working surface must have a smooth finish. 

In some production machines that use a knife-on-plate type of casting head and a granite block casting surface, the granite block is extended into the drying chamber through the "dead zone to the exhaust fan exit. This extension of the uninterrupted flat, smooth, and level zone allows the cast film to form a gel-like structure before it reaches the heated drying chamber. Beyond this point, heavy-... 

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