Tools
To get an idea of the alignment used by the GD&T evaluation with specific datums, right-click on the Datum Category and select “Align”.
You will be prompted to specify the datum scheme, picking primary, secondary and tertiary where applicable. This will then move the instruments and points associated with the datums to the correct orientation based on this datum scheme. Because each feature check is evaluated based upon its own datums it will be necessary to include or exclude only the datums you wish to use in the alignment to simulate the alignment for the particular check. This alignment tool is primarily for visualization and troubleshooting purposes. It will not exactly duplicate the evaluation in all cases. For this reason results should be compared the transform values reported in the feature check summary table.
Datum selection can be set in either of two way in the GD&T Datum Alignment dialog:
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The middle section lists each feature check. If you wish to set the datum scheme to a match that of a particular feature check then the specific check can be clicked on in this list. Doing so will set the datum selection accordingly.
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Using the Evaluate Selected Feature Check and Apply Transform (if possible) check box does just that. It uses the selected check and applies the resulting transform resulting returned from evaluating that particular check. If the solution is fully constrained, this will zero out the fit transform for this particular check. This can be very helpful in troubleshooting or when comparing to the results returned by a relationship.
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The final or “Manual” section allows a datum scheme to be set that is not currently available in the job file or differs from one of the existing datum schemes. You can select and designate any particular datum as primary/secondary or tertiary as needed.
To accelerate and the calculation process and to ensure that an ideal alignment solution is found for a particular check it is highly recommended that an initial instrument alignment, using one of SA’s other alignment tools such as Quick Align to CAD or Relationship Fitting, is performed first prior to performing the check, particularly if using surface datums.