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Tip: Fit Scan Set to Design Model
Select as few surfaces as is reasonable for fitting. Too many fit surfaces can cause overfitting, which can decrease the value of deviation results.
For the best results, select surfaces that will fully constrain all six degrees of freedom.
The system fits the scan set to all the selected surfaces simultaneously. It gives the greatest weight to the primary surfaces and the least weight to the tertiary surfaces. This functionality is very useful in obtaining deviation results about features that have been dimensioned with primary, secondary, and tertiary geometric tolerances.
Imagine a hole in the top of a cube, which is located by linearly dimensioning to the right plane (D1), the front plane (D2), and with a depth dimensioned from the top plane (D3). If geometric tolerances are assigned D1, D2, and D3 as primary, secondary, and tertiary respectively, these must be kept in mind when fitting the scan set. The fit should reference the right side of the cube as a primary surface, the front side as a secondary surface, and the top as a tertiary surface. This yields the most accurate information about deviations of the hole feature.
In situations where another feature—which was dimensioned using different references—is on top of the box, you can create another fit feature using the appropriate surfaces as references.
After you have selected surfaces for a fit feature, you can designate points that you want the system to ignore during the fit calculation. This tactic is advantageous when some points are known to deviate from the design model (so including them in the fit calculation would be detrimental) but their exact deviation is still unknown (but can be discerned during deviation analysis).
After you click OK in the Scan Set Fitting dialog box, Creo Parametric calculates the fit and then adjusts the placement of the scan set accordingly. If multiple fits exist, you can display them with the Display Fit option on the Scan Set Display dialog box.
If you redefine a scan set, and the fit feature needs to be recomputed, you should use the Update Fit option. The system retains all of the previously specified references, but it recalculates the scan set placement to reflect the changes made to the scan set.