I was reading thru the ASME Y14.5-2009 handbook and came across something I haven't really paid much attention to before. In Section 7.4.2, it says
"Where different positional tolerances are used to locate holes and counterbores (relative to common datum features), two feature control frames are used. One feature control frame is placed under the note specifying hole requirements and the other under the note specifying counterbore requirements. See Fig. 7-25. Different diameter tolerance zones for hole and counterbore are coaxially located at true position relative to the specified datums."
I normally dimension true positions for holes and counterbores as 2 seperate true position dimensions, and normally these DRFs are fully constrained so the coaxial requirement is fulfilled because the DRF is allowed to shift. But my question is this:
In the example shown (Fig 7-25), there is no datum that clocks the holes. In PC-DMIS, how would I dimension the holes and counterbores with different true position tolerances while maintaining the coaxial requirement? Since the pattern is allowed to rotate about datum -B-, I'm not sure how to force PC-DMIS to calculate two different true position tolerances using the same rotational shift...
Fig 7-25.jpg
"Where different positional tolerances are used to locate holes and counterbores (relative to common datum features), two feature control frames are used. One feature control frame is placed under the note specifying hole requirements and the other under the note specifying counterbore requirements. See Fig. 7-25. Different diameter tolerance zones for hole and counterbore are coaxially located at true position relative to the specified datums."
I normally dimension true positions for holes and counterbores as 2 seperate true position dimensions, and normally these DRFs are fully constrained so the coaxial requirement is fulfilled because the DRF is allowed to shift. But my question is this:
In the example shown (Fig 7-25), there is no datum that clocks the holes. In PC-DMIS, how would I dimension the holes and counterbores with different true position tolerances while maintaining the coaxial requirement? Since the pattern is allowed to rotate about datum -B-, I'm not sure how to force PC-DMIS to calculate two different true position tolerances using the same rotational shift...
Fig 7-25.jpg
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