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A surface plate is a solid, flat plate used as the main horizontal reference plane for precision inspection, marking out (layout), and tooling setup. [1] The surface plate is often used as the baseline for all measurements to a workpiece, therefore one primary surface is finished extremely flat with tolerances below 11.5 μm or 0.0115 mm per ...
It is done by using a precision surface such as a surface plate or a straightedge as a standard (a straightedge in this context is not a ruler; it is a miniature surface plate of extreme accuracy). The standard is coated with a very thin coating of a material such as Prussian blue. The workpiece and standard are touched together by gravity ...
A typical range of surface roughness that can be obtained without resorting to special equipment would fall in the range of 1 to 30 units Ra (average roughness), usually microinches. Surface accuracy or flatness is usually measured in units of helium light band (HLB), one HLB measuring about 280 nm (1.1 × 10 −5 in). Again, without resort to ...
Up until his introduction of the scraping technique, the same three plate method was employed using polishing techniques, giving less accurate results. This led to an explosion of development of precision instruments using these flat surface generation techniques as a basis for further construction of precise shapes.
Surface plate or marking out table — provides a true surface from which to work; Angle plates — assist in holding the workpiece perpendicular to the table; Scriber — is the equivalent of a pen or pencil. It literally scratches the metal surface leaving behind a fine, bright line; Height gauge or scribing block — allows lines to be ...
Therefore, a very flat and stable work-surface is also needed, on which the test can be performed, preventing both the flat and the test-piece from sagging under their combined weight, Often, a precision-ground surface plate is used as a work surface, providing a steady table-top for testing upon. To provide an even flatter surface, sometimes ...
Granite surface plates are fine for machines with lower accuracy requirements such as a CMM, but passing into millionths of an inch and beyond, cast iron is one of the few choices available for static, long term gage stability. Cast iron masters are used to produce laboratory-grade granite surface plates.
Whitworth popularised the three-plates method for producing accurate flat surfaces (see Surface plate) during the 1830s, using engineer's blue and scraping techniques on three trial surfaces. Up until his introduction of the scraping technique, the same three-plate method was employed using polishing techniques, giving less accurate results.