Let’s begin with roundness. This can also be referred to as circularity and it is the 2D tolerance that controls how closely a cross-section of a cylinder, sphere, or cone conforms to a mathematically perfect circle.
Next, there is cylindricity. This is the 3D version of roundness. It describes how closely an object comes to a perfect cylinder. This includes roundness, but also includes whether the object is straight along its axis. Cylindricity measurements are generally taken when a machine tool operator needs the workpiece to have the same diameter along the full length of its body.
Coaxiality is another important term and it builds upon the first two terms. It is defined as the tolerance for how closely the axis of one cylinder is to another. Coaxiality measures whether the center of one element is along the same axis as that of another element. We should also note that our line of machine tools are able to simplify coaxiality measurements on a machine tool. Check out these tools and their capabilities here.
Runout is another prevalent term in the machine tool world. Runout is a 2D measurement that can be taken either in the axial or radial direction. It is important to note that, when measuring in the radial direction, runout combines both roundness and concentricity deviations into one measurement. Runout essentially takes into account both the axis offset and the roundness of an object rotating around an axis.
Like cylindricity and roundness, runout and total runout are similar, but total runout is the 3D measurement of 2D runout. Total runout is a measurement that takes into account the entire surface of a part and all measurement must fall within a specific tolerance.
Now, knowing what these measurements are and actually carrying them out can be two very different things, but having a firm grasp of what they are is certainly a start. If you work in a machine shop or a facility that uses CNC or machine tools, we’d love to hear your experience putting these measurements into practice on the job and any tips and tricks you have found to be helpful.