Hi I have come across one drawing, which I need to use it as reference to make new one. But in reference drawing one feature has been given as in below image. In another location some other feature has a control like shown in below image. My doubt is, can datum 'E' be moved from teritary datum to primary datum? Can datums be interchanged in GD&T frame? Regards Vinod. B
Datums are just ways of labeling features. They become primary, secondary, tertiary by how they are located in individual feature control frames. A round feature can be a primary datum for the control of some feature. It can be a tertiary feature for the control of yet another feature. It all depends on how the part functions and how you the designer need to control the allowable variation in the part. GD&T is a language, it has many letters and words. You are the author and how you put them together depends on what you want to say.
