We have all seen prints with many datum reference frames on them. The fact that there are multiple sets of datum’s is not an issue and is put in place for functional design reasons. There can be so many that they look like an alphabet soup. But what about raw castings? Generally the functional part datum reference frame(s) have not yet been cut into the parts yet. This where casting datums come into play. They are typically designated as X-Y-Z or Z-Y-X.
Fully defining large assemblies can be a daunting task. It is a task that cannot be ignored, as a well-defined assembly drawing is necessary to properly convey critical details. Manually labeling everything in an assembly drawing can take days and it is very easy for not all the detail to be captured. A solution to this is to add a Bill of Materials or BOM to the drawing. Modern CAD software (Like SolidWorks – shown in the images below) all have automated means to generate BOMs. This helps automate the process, reduce chances for error and allows for automatic updates as assemblies change.