Effective Training Inc. Message Board

I am trying to understand a true position callout on a drawing that I have recently received from my product engineering group as it pertains to the ASME Y14.5M-1994. The intent of one of the true position tolerances is to align five co-axial cylinders in relation to each other.

Currently the true position of the five co-axial cylinders is currently defined on the print as shown in Example 1 of the attachment. I disagree with this call out because the true position has no datum. It is my understanding that true position always requires a datum.

One recommendation from a colleague is shown in Example 2 of the attachment. I am not completely sure that this is correct. I don’t know if changing the datum callout to this position indicates that the five large cylinders are to be treated as one datum.

Example 3 is my recommendation on how to define this drawing. It is very clear that axis of the five cylinders need to be treated as the axis to define the true position of each of the 5 cylinders.

Can anyone confirm my analysis above? I am just looking for a gut check here because I have been going around and around about this issue for a few days now and have not gotten off center with my design group.

P.S. I think there is a way to do this with the CF callout in the new 2009 revision but we have not adopted this standard yet for our designs.

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Anthony J. Weaver
Supplier Development Engineer
BorgWarner Drivetrain Systems