When dimensioning true position for holes and the datum reference frame for them is different than your current alignment, is it enough to just select "Datum Reference Frame" in the alignment dropdown option? Or would I actually have to create another alignment for those holes? Say for example, I had holes on one side of the part that were called out to ABC (my current alignment,) and on another side there are holes called out to BAC. Do I have to create a BAC alignment, or will selecting "Datum Reference Frame" when dimensioning the holes take care of that for me?
Selecting Datum Reference Frame in the dialog window will report your features from the DRF specified. Selecting Current Alignment will report your features from the active alignment, but the calculation will still be performed using the DRF specified. If your active alignment is per the DRF specified, the report will be the same regardless of the option specified.
don't you need to build the DRF to get the MMB for the datums (if applicable)? And if there is MMB, then there will be a difference in the reported deviations.
So I don't need to create another alignment then because the true position calculation will always be done from the DRF, regardless of the current alignment?
ESchertzMatthew D. Hoedeman My statement holds true if you're using XactMeasure GD&T (pre 2020 R2) or the Geometric Tolerance command (2020 R2+). If using Legacy dimensioning, you must create the dimension while your active alignment matches that defined by the DRF. If you have a material modifier specified on a datum reference, you should avoid using it if you're using Legacy dimensioning as the calculations are not correctly performed.
I think the disconnect I had in this thread is the "current alignment" mentioned by the OP. I just want to make sure that everything is 100% clear on this topic to try to avoid confusion, now and in the future.
That being said, I only use legacy reporting.
IF you select "use current alignment" in either Xact or GeoTol (and do not build the DRF for the dimension), then the datum MMB is ignored, and thus giving the same results as legacy, correct?
If you build a DRF then it ignores the current alignment completely and all calculations are based on the constructed DRF, correct?
And yes, the 'USE DATUMS' option for legacy is FUBAR, always has been.
Matthew D. Hoedeman If you select Current Alignment in XactMeasure or Geometric Tolerance, the material modifier on the datum reference is not ignored. The only change is in the reporting. The calculations performed (datum shift) are the same. It doesn't matter what your active alignment is, the two commands will do their own calculations and report the feature in the chosen coordinate system.
