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True surfaces
Motorcycle enthusiasts may, for example, need to check the relative trueness of sliding surfaces such as carburettor slides, or check how flat mating surfaces, such as crankcase halves, are.
Going back in engineering history, workers who wanted precise, flat surfaces would use a three plate (item) method and polishing, by checking or polishing two flat surfaces against each other then regularly and randomly rotating the pair of surfaces with the third (idle) surface, a reasonable degree of accuracy was achieved.
During 1830-1840, (Sir) Joseph Whitworth (1803-1887), of British Standard Whitworth threads and Whitworth rifle, fame achieved greater accuracy of flat surfaces by again using a three surface approach with scraping methods and ‘Engineer’s Blue.’ The Whitworth techniques were well publicised in period and adopted by many engineers.
From this start, the Whitworth techniques have been adapted for a vast number of engineering roles, from the above mentioned carburettor slide to the matching of mould cores to cavities and far more. Often Engineer’s Blue is used, but in some instances, different coloured preparations are employed to suit the task and the colours of materials involved.
Commonly, Engineer’s Blue is a blend of Prussian Blue pigment with a non-drying thick liquid or soft solid, such as oil or soft grease. But there are many variations of the Engineer’s Blue we might use at
