I'd like to discuss perpendicularity of a 6.0mm datum hole or 6.0mm X 12.0mm slot in sheet metal. I've noticed this call out before only more frequently as of late. Generally on Ford prints. Mind you, there is not much of a cylinder here when the material thickness is 1.5mm give or take. Usually, the call out is accompanied by flatness or profile on the same surface as the hole or slot. The question was brought up "What are the engineers really looking for?" The norm has been to apply TP of the datum hole or slot back to -A-B-C- MMC. My question is how do they expect us to check perpendicularity of a slot in a surface back to the same surface w/o measuring a true cylinder? Any thoughts please?

Regards,

Geoff
Sr. CMM Programmer
Lapeer Metal Stamping
LMS Metrology Lab
Lapeer, MI