A note about part alignment

aPriori requires that the two CAD models have a common “base” coordinate system. This is because aPriori will align the two CAD models using their base coordinate systems, and then attempt to determine the differences between them.

To check for misalignment

There are three ways to check whether the CAD models use the same base coordinate system:

1 In the CAD system, ensure that both models are aligned the same way. (Specific procedures are beyond the scope of this aPriori documentation.) Doing this and correcting any problems before you attempt the 2-Model Machining costing is the preferred way to avoid this issue.

2 In aPriori, visually inspect the Source Model GCD (see Source model GCD on page 757). This can only be done after you have attempted to cost the finish-machined model. It is better to use the CAD system method described in the previous paragraph, prior to costing. But if you have already costed the parts, click the Source Model GCD to display it, and see if it appears to be positioned correctly with respect to the finish machined model.

3 In aPriori, check the Costing Error messages. Again, this can only be done after you have already attempted to cost the finish-machined model. aPriori displays a Costing Error message similar to: “Parts are seriously misaligned. Source and final CAD models must be aligned on the same coordinate system” in the Manufacturing Process pane if it believes that too great a percentage of the finished model protrudes beyond the boundaries of the source model, indicating a likely misalignment of their respective base coordinate systems. By default this threshold is set to 18%, but can be controlled by the plant variable Misalignment Cutoff Percent.

To correct misalignment

If the source model and finish machined model do not use a common base coordinate system, you must correct this situation inside the CAD system. Specific steps are beyond the scope of this documentation, but consider the following discussion when deciding the approach you should take in your CAD system:

Typically, the finish-machined CAD model is created by first merging in the geometry of the raw (unmachined) part, and then adding in a variety of cuts and hole features to represent the material that is machined away.

If your finish machined model was created in such a manner, then you can use this to your advantage to create a new model of the raw (unmachined) part that will have the same base coordinate system as the finished model. To do this:

1 Save a copy of the CAD file to a new name.

2 Suppress or delete the features that occur AFTER the merge of the raw unmachined geometry.

3 Save the file again. At this point, the geometry of the new CAD file should look identical to the CAD file that represents the raw/unmachined part, but it will have the same base coordinate system as the machined part.

4 In aPriori, cost this new CAD file in Casting, Forging, or whatever process group is appropriate, and supply its scenario as the “Source” model instead of the original CAD file.

5 Repeat the steps described in “To check for misalignment” above to verify that the misalignment has been resolved.