I've been having an issue measuring concentricity. Could someone explain best practices for checking concentricity between two holes/pins at opposite ends of a part? The parts very from 4" to 12". I can spin them on the datum on my V-Blocks and show them as basically perfect with an indicator (indicator/v-block has been certified), but when I run them on the CMM I show them as being out of tolerance by like.. 1mm~/0.040". I have no idea if I'm just setting up the feature wrong or what, any thoughts?
Seems like you might have found the problem. But just a side note, PC-DMIS evaluates concentricity as TP. If you actually want to measure true concentricity on the CMM, it can be quite cumbersome. You would have to measure using diametrically opposed points at an infinite number of cross sections across the entire surface of the measured features. Then construct mid points at each cross section. Then report the deviation from center. This would give you the error at the center at each cross section.
Seems like you might have found the problem. But just a side note, PC-DMIS evaluates concentricity as TP. If you actually want to measure true concentricity on the CMM, it can be quite cumbersome. You would have to measure using diametrically opposed points at an infinite number of cross sections across the entire surface of the measured features. Then construct mid points at each cross section. Then report the deviation from center. This would give you the error at the center at each cross section.
If you are using the Geometric Tolerance command and referencing ASME Y14.5, you are able to choose whether concentricity is evaluated as median points or the axis method.
You would have to measure using diametrically opposed points at an infinite number of cross sections across the entire surface of the measured features. Then construct mid points at each cross section. Then report the deviation from center. This would give you the error at the center at each cross section.
This is the median points method.
The axis method is the same as position and is the method that the older XactMeasure command and legacy dimensions use.
