What is Cylindricity and why measure it?

Cylindricity values are becoming more important in the measurement of components particularly as an aid to improve the efficiency and cost effectiveness of systems. Of particular note is automotive fuel injection, where the need for greater economy is demanding greater precision in components.

There are many ways of defining cylindricity of a component. A good example is the minimum zone method of analysis. This can be described as the radial separation of 2 co-axial cylinders fitted to the total measured surface under test such that their radial difference is at a minimum.

For the purposes of inspection, a tolerance may be put to the cylindricity analysis and in the above case may be written as "the surface of the component is required to lie between 2 co-axial cylindrical surfaces having a radial separation of the specified tolerance".