Concentricity tolerance controls the central axis of a cylinder or sphere with respect to datum plane/axis. It also controls the median points of a cylindrical parts. For example transmission gears. Refer this article to understand the basics of geometric tolerance.
Datum plane, surface or axis is required to define concentricity tolerance. LMC and MMC modifiers are not applicable with concentric tolerance.
Concentricity tolerance creates a 3-dimensional cylindrical tolerance zone around datum axis. All central points of the circular feature must lie in this tolerance zone.
How To Measure ?
Step-1 : Identify and fix the part on datum.
Step-2 : Plot controlled surface outer profile. CMM can be used to create the profile.
Step-4: Determine the central points of plotted profile at various cross sections.
Step-5: Verify position of central points. All points shall lie within given cylindrical tolerance zone.
To sum up, Concentricity tolerance controls the central axis of a cylinder or sphere with respect to datum plane/axis. It is very difficult to measure. Therefore runout and position tolerance are used as alternative
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