A Surface Plate is a solid flat plate manufactured to be used in the mechanical industries specifically in the shop floors and calibration laboratories. They are used daily for mounting mechanical gauging systems and are helpful during calibration of various gauges. In manufacturing sectors, it is the easiest and quickest way to set a reference gauge thereby saving a lot of time. To be simple there cannot be a quality control room without a surface plate.
What are Surface Plates made of?
During World War II, Surface Plates were made from metals such as cast iron, steel etc., later Surface Plates were made up of superior crystalline rock which are fine grained and are completely non-porous otherwise known as granites.Â
There are several different kinds of granite suitable for manufacturing Surface Plates such as black, grey, light grey and pink granites. Black Granite is generally recognised as the best option, because of its preferred characteristics: low porosity and moisture absorption, lowest coefficient of thermal expansion, uniformity of texture, non-abrasiveness, easy resurfacing, non-glare surface and most importantly, it provides an easy-to-clean surface that resists stickiness thus making it easy to slide. Black Granite is highly desirable for maintaining accuracy and stability and has a lower maintenance cost.
Specifications of a Surface Plate?
Granite Surface Plates are manufactured in various grades to match their intended applications: Grade ‘0’ is precisely used in the calibration laboratory or control room to maintain the accuracy. Grades 1, 2 and 3 are used in the shop floors of the manufacturing units. Grade 0 is twice as accurate than Grade 1 and similarly Grade 1 is twice as accurate than Grade 2 and so on.Â
A flat surface is extremely imperative, but a surface plate of high accuracy can only be generated by people who are skilled in the techniques of hand lapping. Jafuji’s manufacturing unit, has skilled experts who deliver granite surface plates with high accuracy and customize as required.Â
There are also Surface Plates available with Bench Centre Setup to reduce space consumption. The flatness is checked using an electronic level with a sensitivity of 0.001mm/m which is manufactured by Wyler to ensure the accuracy. To give context this roughly translates to 1mm/Km.
How should you maintain Surface Plates?
Surface Plates are used as a baseline for all measurements and should be calibrated regularly: at least once in 6 months to ensure their accuracy. Use a mild cleaning agent to clean the granite surface plate. There are two calibration methods generally in use; one is the Grid Pattern and the other is the Diagonal Method or Union Jack Method. The graph below helps illustrates the Flatness deviation in the surface plate.
The above graph helps the manufacturer or the engineer in the quality room to understand the flatness of the surface plate. The high points indicates that the surface is not flat hence can be lowered by lapping.
The below figure and the graph is an another illustration of calibration using the Union Jack Method
Nowadays we often look to technology for advancements in engineering. However, one of the best tools for accurate measurements is far simpler than any machine. The surface plate is, in fact, nothing but a humble igneous rock made to be perfectly flat. It is simple in its design and principle, yet a surface plate is a game changer for precision inspection.
