yang686526

profile of a surface to define a hole pattern?
can i use a profile of a surface call out to define the outer profile as well as a hole pattern of a stamped component? all dimesions would be basic.
i've been told that i must use position to define the holes.
the outer profile should be ok, but not the hole pattern.
basic dim the holes, then position.
chris
sr. mechanical designer, cad
solidworks 2005 sp0.1
asme y14.5m-1994 is flexible enough that you can specify all of your dimensions as basic and apply the tolerance requirements as a profile tolerance for both the outer profile and holes. the profile tolerance zone would be applied to the basic definition of all the features (either bilaterally or unilaterally as indicated by the callout) and the actual produced features must reside within this zone for the part to be acceptable. for the holes, the profile tolerance would not only define their location, but their size and form as well.
the down side to this type of application is that it does not accurately reflect the typical functional requirements for a fastener hole; where size and location of the hole are separate considerations. usually, the fit required for the fastener is determined by the hole size and location is determined by the assembly requirements of the holes to a mating part. this separate consideration is also what allows us to invoke mmc principles on the hole positional tolerance and take additional (bonus) tolerance as the holes depart mmc. you lose the capability of specifying mmc tolerance on the hole pattern and essentially rob yourself of available part tolerances.
so, even though you can use a profiile in specifying the tolerance for the hole pattern, you actually gain more usable tolerance by using a positional tolerance in this application.
gdt_guy
this all makes sense; not illegal but not the best approach either. thanks.