Roundness, or circularity, is the 2D tolerance that controls how closely a cross-section of a cylinder, sphere, or cone is to a mathematically perfect circle. Consider a cylinder whose purpose is to roll along a flat surface. A small flat on the OD of the cylinder would detract from how smoothly the shaft can roll. The flat spot can even be so large that the shaft cannot roll at all. In this case the flat represents a deviation from a perfect circle that can be measured quite accurately.

An example of a more complex roundness error is called lobing, which is an unintended form error from a centerless grinding operation. Roundness callouts on drawings have no reference to a datum, as roundness does not relate to the cross-section’s location on the part. The actual measurement of these parameters can be quite complex. They require the proper selection of reference elements and filtering techniques, which help in interpreting the collected data.

J.A. King offers roundness measurement services at several locations throughout our network of ISO 17025 accredited inspection laboratories. Our technicians have years of experience working with a variety of part types and are ready to help you find the measurements you need to ensure your parts are within tolerances.

For more information about our roundness measurement services or to receive a service quote, fill out the form using the button below and discuss your project with a J.A. King team member:

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Also, take a look at our article about the differences between roundness, cylindricity, coaxiality, concentricity, runout, and total runout.

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