◎ Concentricity

How to verify

The classic method is a dial indicator with the part in a V-block: rotating the part and measuring at two diametrically opposite points in each section, half the difference between those readings approximates the center of that section. A CMM calculates the actual median points of multiple sections and compares them with the datum axis. In everyday shop practice almost nobody measures concentricity literally: it is replaced by circular runout (faster and more repeatable) or by axis position at MMC, which is what ASME Y14.5 has recommended since 1994 and what the 2018 edition formalizes.

Workshop guideline values

General

0.05–0.15 mm on stepped diameters in general machining.

Accuracy

0.02–0.05 mm on shafts with several close-fit diameters.

High precision

0.005–0.01 mm on rotors or precision shafts.

Guidance only: the drawing's value always wins.

Common mistakes when interpreting it

• Measuring it literally, point by point with an indicator, in series production: in practice almost nobody does this because it is so slow; circular runout, which is much faster and more repeatable, is used instead.
• Confusing it with coaxiality: concentricity compares the centers of individual sections, not the full axis — they are conceptually different even though they share a symbol.