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Reporting Datum Target Dimensions

Reporting Datum Target Dimensions

Reporting Datum Target Dimensions

(OP)
I have a drawing with datum targets thats similar to what I have attached with 3 bolt holes inside the profile. I need to do a first article inspection on this part and I dont know how I should inspect and report these dimensions for the datum targets. I am using an Optical CMM and I just use the bolt holes as a datum alignment so I dont need to use the profile. I can use the 2 outside radii as datums but the 45 degree and Basic .212 do nothing for me. How would I go about inspecting this part with these datum targets and how would I report them? Or do I?

RE: Reporting Datum Target Dimensions

Basic dimensions should not be inspected and reported. In this case they are telling you how the datum targets look like and how they are located relative to each other.

RE: Reporting Datum Target Dimensions

(OP)
I understand that basic dimensions are usually not reported but on First Article reports for Aerospace Im being required to report everything even if its not a rejectable requirement. So knowing that, are datum targets like this intended to be inspected at all? Would I use this information for anything if I have a CMM?

RE: Reporting Datum Target Dimensions

It's true that basic dims don't get reported. And as pmarc wrote, the same is true for datum targets. This is because there is nothing to measure with datum targets; they merely tell you how to "hold" the part in your CMM for some other tolerance that will reference B and C (or maybe B-C).

Think of a regular datum, symbolized by a triangle. When you see a triangle symbol for datum A, you don't report anything -- it's just telling you which surface to zero out on. The same thing applies here! The only difference is that with datum targets they're getting a little more picky about which portions of a surface you probe in order to establish a datum.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

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