In addition to primary and secondary setup axes (see Principal Setup Axes) aPriori creates two rotational setup axes for use only with machines that have at least one rotational axis. They represent the way the part is oriented on a given rotational machine (such as a 4- or 5-axis mill) when the setup axis is parallel to the machine’s axis of rotation.

For a 4-axis mill, the first rotational setup axis is chosen so as to maximize the number of features it makes accessible (that is, the first rotational setup axis is the setup axis that is normal to the greatest number of other setup axes). The other rotational axis is in a direction that is normal to the first rotational axis; aPriori chooses the normal whose name has the lowest numbered suffix (so, for example, if SetupAxis:4, SetupAxis:8, and SetupAxis:99 are all the normals to the first rotational setup axis, aPriori chooses SetupAxis:4 as the second rotational setup axis).

For a 5-axis mill, the two rotational setup axes have the same directions as the two principal setup axes; they are essentially copies of the primary axes.

Note that, for these rotational machines, the rotational motion differs from turning in these two respects:

Note also that, for a 4-axis mill, the tool approach is perpendicular to the rotational axis.