Concentricity vs. Cylindricity — What's the Difference?

Concentricity is a geometric tolerance that specifies the center alignment of cylindrical features to one another, ensuring symmetry in mechanical parts. It is critical in components requiring precise alignment, such as in engines and shafts. Whereas cylindricity, another form of geometric tolerance, focuses on the 3D aspect of a feature, ensuring that any point on a cylindrical surface is equidistant from a central axis. This is vital for parts that must fit into others with minimal clearance, like hydraulic cylinders.

While concentricity is often considered one of the most complex and stringent tolerances to measure and achieve due to its requirement for perfect symmetry, cylindricity offers a different challenge. It demands the surface of a cylinder to be perfectly round and straight along its entire length, which can be just as difficult to manufacture consistently.

The inspection process for concentricity involves comparing the centers of two or more features, typically using a coordinate measuring machine (CMM) to ensure precision. On the other hand, cylindricity is checked by evaluating the surface variation along the cylinder’s entire length and around its circumference, often requiring specialized equipment.

Concentricity is crucial in applications where balance and rotation are key, affecting the performance of rotating machinery by minimizing vibration. Cylindricity, however, is more about the smoothness and uniformity of motion, especially in telescoping components, ensuring a snug fit without binding.

Despite their differences, both concentricity and cylindricity are vital for the quality and functionality of precision-engineered components. While concentricity ensures the centered relationship between different cylindrical parts, cylindricity guarantees that each part's surface is ideal for smooth operation.