Datum shift

[Viper555]

Hello,

I'm trying to understand an illustration which uses datum shift to show one possible "means this". I'm referring to Fig 7-58(c) in the 2009 standard. The illustration shows the VC for both cylinders, but it's the location of the three vertical lines relative to each other that I don't fully understand. If you were to apply the datum shift to the max extent possible (at LMC for Datum Feature A), then the part would shift to the rightmost position of the .1 cylindrical tolerance zone and is denoted by the .05 radial distance between the Datum Axis A and the datum feature A. This is clearly shown.

Why then does the distance between the upper cylinder at its leftmost location position mate up with the boundary edge? It seems the .45 distance between the upper cylinder feature axis and Datum Axis A would be reduced to .40 since you would be taking .05 away due to the shift. I'm not saying you lose your total positional tolerance, but rather you would have .40 to the left of the Datum Axis A and the remaining .05 to the right.

Thanks in advance.

 

[3DDave]

Datum shift is applied solely to the datum feature. The measurements are made from the datum feature simulator, not the as-made feature.


The datum feature is shifted in the datum feature simulator. The controlled feature is allowed to move in the Virtual Condition boundary.