Determining derived median line

[Medmaker]

I've been trying to wrap my head around the details of determining the derived median line when it comes to things like straightness. I understand the concept of using opposed point measurements and finding the center point of that line element and then creating a "line" through those points. Where my understanding falls short is that it seems as if that only determines the derived median line in that one radial plane. Do you need to then repeat that process along other planes that are radially disposed from one another? If that's the case, don't you actually end up with multiple derived median lines? From what I've read, I think I should be determining the centerpoint of the cross sections along the length of the feature and then using those points to determine the DML. However, I haven't really found reference to how that is done. Is this a case where there is a mathmatical way that may differ from an everyday way?

Thanks for the help!

 

[pmarc]

Have you looked to paragraph 1 of ASME Y14.5M-1994, especially to definition 1.3.16? I think it clarifies your dillemma quite well, unfortunately without offering any details on how the cross section center points are determined. For this you need to look to ANSI B89.3.1.