So far in our datums disccions we been talking primarily about surfaces. However

Question

So far in our datums disccions we been talking primarily about surfaces. However, what about axis datums? When would I want to use an axis as a datum. Remember, datums are not dimensions, they are referenced with dimensions. Image I had a part with two holes through a really thick part and I wanted the axis of both of them to be parallel to each other. I could call the center axis of one of the holes DATUM A. I could then apply a tolerance to the axis of the second hole in relation to DATUM A, therefore controlling the parallelism of the two holes. Anyone else? Why would I ever want to reference an axis as a datum?

Explanation / Answer

Datum Axes:

For the control to be axis oriented, the object should be situated on the side of a diametric tolerance. This would mean that the datum is nothing but an axis through centroid of the feature, instead of the surface this time. Datum axes are presistent with Geometric Dimensioning and Tolerancing systems which are run by controls of axes such as run-out, perpendicularity or concentricity. The concept of Datum axes arises when we rotate a par by a surface, located by a diameter, and it has an angular relationship relative to a FOS. When comparing the datums with the face primary, diameter secondary (RFS), and slot tertiary (RFS), the following conditions can arise:

For rest of the part, please share the shape discussed by your teacher in the class too.

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