When aPriori analyzes a part and performs GCD extraction, it chooses certain orientations to serve as the principal setups. There are two principal setup axes, which have the values PRIMARY and SECONDARY, respectively, for the property Setup Type. The first principal setup orients the part top up, and generally allows operations to be performed on the top of the part, while the second principal setup orients the part top down, and generally allows operations to be performed on the bottom. (Sides of the part can also be accessed by tools approaching from the primary or secondary setups, or by additional setups.)

aPriori chooses principal setup axes by using a heuristic to choose a top for the part. Very roughly, the top is chosen so as to maximize the surface area accessible from directly above, when the part is upright (that is, when the part is oriented with the top up). The actual quantity maximized is a weighted sum of the surface areas of accessible GCDs, weighted by GCD type (for example, planar faces are weighted more than curved surfaces), as well as by accessibility type (for example, a normal-accessible planar face is weighted more than an oblique-accessible planar face).

For rectangular machining stock, you can direct aPriori to choose the directions along the shortest stock dimension instead, by setting the site variable useShortestStockDimentsionForPrimarySetup to true. In this case, aPriori chooses directions along the shortest dimension of the part’s bounding box to serve as the principal setups. Of the two principal setup axes, the primary axis is the one that, roughly, maximizes the surface area it makes accessible. As with the default configuration, the actual quantity maximized is a weighted sum of the surface areas of accessible GCDs, weighted by GCD type, as well as by accessibility.

When aPriori chooses a primary setup axis, it is choosing a part-relative direction, top-wards. When you view a part in the component viewer, and select SetupAxis:1 in the Geometric Cost Drivers pane, the viewer displays an arrow pointing top-wards.

The direction indicated by the arrow is the part’s primary setup axis. It represents the way the part is oriented on a given machine when the setup axis points in the direction from which the tool approaches.

The part’s secondary setup axis, SetupAxis:2, is bottom-wards, which points in the opposite direction.

The primary and secondary setup axes (top-wards and bottom-wards) serve as the part’s principal setup axes.

If you show active setup axes for a part (see Displaying Setups, Associated Operations, and GCDs), the component viewer displays the principal setup axes (as well as any other active setup axes—see System-activated and User-activated Setup Axes). You can override aPriori’s choice of principal setup axes—see Overriding Principal Setup Axes.

To override aPriori’s choice of principal setup axes, follow these steps: