In some cases you may want (or need) to start from a single CAD part and then transition to 2-Model later. For example, you may have the finished model CAD file in hand, but the forging or casting input model CAD file may not be available for another month. In this case, you can proceed by costing the finished model by using the Casting or Forging process group and specifying tolerances and/or machining operations for specific GCDs as appropriate.

Or perhaps you have a legacy part that you costed in the Casting or Forging process group, including tolerance and surface roughness information for many GCDs.

In either case, when the raw input CAD model becomes available, you can switch the existing model to the 2-Model Machining process group, and specify the newly-available cast or forged part to be the source model.

When you switch the process group from Casting or Forging to 2-Model Machining, aPriori attempts to preserve the GCD numbering and any user overrides assigned to those GCDs, such as tolerance and roughness requirements. However, you should check the Cost Overrides Summary dialog (see the "Working with the Overrides Summary dialog" section of the aPriori User Guide) to ensure that no significant overrides have been lost.