As you all can see there are multiple ways of controlling size and location of a pattern of slots.
First of all, I see no mention of the functional engineering requirements of the pattern of slots.
So, I would ask, what are the requirements?????
1) Does the pattern of slots interface with an equal nummber of "male" features?
If "YES" then I ask;
1a) Are the male features similar in shape, as in, elongated?
If "elongated", then the entire perimeter of the slot is considered to be a mating
surface. In this application either profile of a surface or positional tolerance is
applicable. Either control will define an inner boundary (virtual condition) which can be
checked with a functional gage. The outer boundary can not be verified with a functional
gage.
2a) Are the male features cylindrical pins?
If "cylindrical" such as a pin, then it is likely that the width inner boundary is more
critical than the slot length inner boundary. Applying a profile tolerance would apply a
constant width tolerance zone around the perimeter of the slot(s). While this is not
technically incorrect, it is likely overly restrictive based on the functional
requirements. What I mean is that the slot can likely tolerate more boundary tolerance
in its length than it's width, but the profile control is not capable of a variable
tolerance zone length vs. width. Positional tolerancing (boundary concept) is capable and
also benefits from the additional tolerance based on slot size departing from MMC(bonus
tolerance).
If "NO".......the slots do not have mating male features then there is not a functional interface to consider. The slots might be weight reduction, or they might be ventilation slots.
2c) If there is no mating condition for the slots and they are weight reduction or
ventilation then the engineering requirements are much different from the scenario above in
2a and 2b. If "venting" for example the size may be of more importance to generate the
combined minimum air flow. The location of the slots is secondary. In this scenario I would
suggest controlling size with a size dim and related size tol, and use positional tol to
control location. As in above, a functional gage could check the inner boundary of the
slot regardless if profile or position is used.
While this only covers some of the possible engineering scenarios, I hope it sheds light on the importance of considering the engineering/functional requirements before applying geometric controls.
Regards,
Gordy