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I believe the DRF in the attached screenshots is fully constrained thru the Datum A Cylinder and Datum B Cylinders, thus leaving Datum C to do nothing. However, if there is an interpretation of ASME Y14.5-1994, I would love to hear it.
The function of the part is as follows: the part rotates into position about the A axis, then 2 pins eject from the mating part into the B diameters.
All un-dimensioned surfaces have a profile to ABC.
Thanks in advance....
"[COLOR=#333333]thus leaving Datum C to do nothing. " - Except for an undimensioned feature which is tolerance controlled to a Profile A (primary), B (Secondary) and C (Tertiary).
The note (Profile) could be improved... e.g.
All untoleranced features shall be dimensionally controlled to a Profile of Surface [/COLOR][COLOR=#333333]A (primary), B (Secondary) and C (Tertiary).[/COLOR]
Thx. The actual note on the drawing states this, but this was not the question. I’m looking for confirmation that C has no affect on the datum structure because A and B control all 6 degrees of freedom.
[QUOTE=tomoakes;17084]Thx. The actual note on the drawing states this, but this was not the question. I’m looking for confirmation that C has no affect on the datum structure because A and B control all 6 degrees of freedom.[/QUOTE]
ASME Y14.5-1994, paragraph 4.5.8 and associated graphics Figure 4-22.
Yes, datum A and B could be used to define and create/control lockdown of all six degrees of freedom. However, due to common confusion I don't recommend this practice.
Key words "when part function dictates".