A turning axis in aPriori represents an axis of revolution for rotationally-symmetric features that may be machined by turning. For a turning machine (such as a lathe) it specifies a setup that orients the part so that the part’s turning axis coincides with the machine’s turning axis. Turning axes come in pairs; the axes in a pair coincide with one another and have opposite directions, and each represents a part-centric clamping direction, either left-end or right-end.

aPriori automatically creates candidate turning axes during geometry extraction. How many are automatically created depends on both the geometry of the current part and the current process group (see System-created Turning Axes). Users can request the creation of additional turning axis pairs by using the Modify Turning Axes dialog (see User-defined Turning Axes).

GCDs and turning axes are related by the Is About relation, displayed in the Geometric Cost Drivers pane.

For Bar and Tube parts, aPriori creates a pair of turning axes along the centerline of a round, square, or hex bar or tube. Turning is not supported for other types of bar and tube stock.

For stock machining, aPriori creates a turning axis pair along the centerline of a round bar or tube. You can also specify user-defined turning axes for round, square or rectangular stock—see User-defined Turning Axes.

For other process groups, aPriori creates one or more candidate turning axis pairs, very roughly, by identifying a direction that is both (1) normal to the largest planar faces and (2) co-directional with the axes of symmetry of the largest axisymmetric GCDs. It then creates turning axes that coincide with the axes of symmetry of the largest (greatest surface area) GCDs with convex surfaces. For Casting and Forging, all automatically-created turning axis are parallel to one another.

The default maximum number of system-created turning axis pairs is determined by the site variable maxNumTurningAxes, which is set to 1 in aPriori starting point VPEs. You can override this number for a specific part, if your part requires two or more different (but parallel) turning orientations (as with camshafts, for example). You can also override this maximum to specify that a part should not be turned. See Limiting Turning Axes.

In addition, for the casting, forging, and 2-model process groups (as well as for stock machining—see above), you can specify additional, user-defined turning axes. Do this, for example, if your part requires a turning axis that is not parallel to the system defined turning axes. See User-defined Turning Axes.

Some parts require turning axes that are not automatically created by aPriori (see System-created Turning Axes). Consider, for example, the following:

Stock machining, off-center, turnable feature: system-created turning axes for stock machining are always along the stock center line. (The allowable distance from the part center of mass is determined by the site variable maxTurningAxisEccentricity, 0.05 in aPriori starting point VPEs.) If your part requires off-center turning axes, specify user-defined turning axes.

Stock machining, turnable feature in square or rectangular stock: there are no system-created turning axes for square or rectangular stock. If your part uses square or rectangular stock and has turnable features, specify user-defined turning axes.

Non-parallel turnable features: system-created turning axes for a given part are all parallel to one another. If your part has non-parallel, turnable features, specify user-defined turning axes.

Follow these steps to specify user-defined turning axis pairs:

You can remove a user-defined turning axis pair by selecting an axis in the pair and clicking Remove.

Follow these steps to specify the number of system-created turning axis pairs for the current part: