Applying Datums to "Stock" Features 1

[RPars]

Hi All,

New user here! We are working on a frame design that is comprised of 2" x 6" x 1/8" wall rectangular extruded aluminum tubing that follows the Aluminum Association tolerances. There are several holes that need to be drilled through the 2" wide tubing for attaching other components.

Is it appropriate to apply datums to the stock outer surfaces of the tubing? The large 6" wide outer face would act as Datum A and the smaller 2" wide outer face would act as Datum B. The goal is to apply perpendicularity tolerances to the cut ends of the tubing as well as true position tolerances for the machined holes. If it is appropriate to apply datums to the stock outer surfaces, are we required to provide a flatness tolerance on Datum A and a perpendicularity tolerance on Datum B in reference to A? We know the flatness and perpendicularity tolerances from the A.A. standards, so we could just use those values. Note that the outer size dimensions of the tubing are provided in the drawing using the "STK" callout.

Many of the previous discussions around stock materials in regard to GD&T are focused more on machined or sheet metal parts. I have yet to come across anything discussing rectangular tubing like this scenario.

Thank you!!

 

[3DDave]

Fair game as datum feature references, less so to put geometric controls on stock features.

 

[RPars]

Thanks 3DDave! I was going back and forth on the geometric controls on the stock features. The way I understand it and learned it from my textbook: "Datum features have flaws just like any other features and must be controlled with tolerances." That being said, the datum features are controlled using the tolerances of the Aluminum Association, so it makes sense that applying them to our drawing could conflict with the original stock tolerances.