GD&T for small features/non-features

[AMontembeault]

I have a number of parts for which vendors supply scribe lines on surfaces, used for the purposes of alignment at the assembly level. These scribe lines are typically called out as having a maximum depth and width, but could be produced with no discernable dimensions (for example, a scribe line made on machinists blue).

I could control these lines with a combination of location and form tolerances, or perhaps with composite surface profile, and it would probably be legal from a GD&T standpoint, however I'm concerned that given the small depth and width of a scribe line, these features would be very difficult to inspect with a CMM to those types of tolerance controls. I'm also keeping in mind Y14.5-2018 and its stance on limit dimensioning for location.

Has anyone come up against something like this before? How did it work out for you?

 

[chez311]

I'm interested to hear others opinions on this, but it sounds like something that may require a special note and/or an internal spec/standard to be fully compliant. Perhaps not but it seems to me you may run into difficulty as you say applying controls to features which essentially have nearly imperceptible physical edges/size except that which could perhaps be picked up by a profilometer or other device which can measure surface finish.

As far as inspecting orientation of these scribe lines, one thing that comes to mind is an optical comparator or similar vision/scanning device.

*Edit: spelling