What is the best way to measure the concentricity of a part?

2 How to define concentricity?

Concentricity is defined as the condition where the median points of all diametrically opposed elements of a feature of size are congruent with the axis of a datum feature. In other words, it is the distance between the center of a feature and the center of a reference feature, measured along any radial line. The smaller the distance, the higher the concentricity. Concentricity is expressed as a tolerance zone that surrounds the datum axis, within which the median points of the feature must lie.

4 What are the advantages and disadvantages of each method?

When measuring a part, each method has its own advantages and disadvantages based on accuracy, speed, cost, and complexity. For example, using a dial indicator and a fixture is simple and low-cost, but it is also time-consuming, prone to human error, and limited by the resolution of the dial indicator and the fixture. Using a CMM is accurate and reliable, but it is also expensive, slow, and requires a skilled operator and a controlled environment. On the other hand, using a laser scanner or a vision system is fast and flexible, but it is also costly, sensitive to ambient light and noise, and requires a high-resolution scanner or camera. In addition, it may not work well for shiny, transparent, or curved surfaces.

5 What are some common errors and pitfalls to avoid?

When measuring concentricity, there are some common errors and pitfalls to be aware of. It is important not to confuse concentricity with other GD&T terms, such as circularity, cylindricity, runout, or coaxiality, as these terms have different definitions and applications. Additionally, concentricity is a very strict and difficult requirement and should only be used when necessary and feasible; otherwise, it can increase the cost, time, and complexity of the measurement and the manufacturing process. Moreover, it is essential to use the correct datum or reference feature for concentricity as this should be the most important or functional feature of the part. Lastly, one must ensure that the method or equipment used for concentricity is suitable for the part and feature and has been calibrated and verified. Otherwise, errors, variations or damage to the part or equipment may occur.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?