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Roundness, cylindricity, coaxiality, concentricity How to differentiate

2023-05-18

 In the manufacturing industry, some people once estimated that circular workpieces are more common than flat workpieces, ranging from screws, nuts, gaskets, to cylinders and bearings. The application of circular workpieces is indeed very high.

For these rotating components, the most urgent issue that needs to be addressed is how to evaluate their true circular shape. Today, we will introduce the symbols and definitions related to roundness (reference standards: ISO/DIS 1101:2017, ISO 5459)

Roundness
The extraction of the circumference should be limited to a tolerance zone between two coplanar concentric circles with a radius difference of t

Straightness
The edges extracted from the cylindrical surface should be limited to the tolerance zone between two parallel lines with a distance of t in the specified direction

Flatness
It is the area between two parallel planes with a distance of tolerance value t.

Cylindricity
The extraction of cylindrical surfaces should be limited to the tolerance zone formed between two coaxial cylindrical surfaces with a radius difference of t.

Concentricity
The extraction center of a circle should be limited within the tolerance zone formed by a circle with a diameter of t that is concentric with the reference.

Coaxiality
The extracted axis should be limited within the tolerance zone formed by a cylindrical surface with a diameter of t that is coaxial with the reference.

verticality
The extracted axis should be limited to the tolerance area formed by a cylindrical surface with a diameter of t and perpendicular to the reference plane