Effects of equate alignment on parallelism?

Warm up the Height gage, polish the indicator tips and take that baby to the surface plate! (sorry can't help with equate alignments) 
We would always double check those questions with an indicator though... Often just grabbed the dial height gage and used it right on the CMM. 

The most I was getting with an indicator was 0.038.  So either equate alignments don't work well for orientation tolerances that tight or (more likely) I'm doing something wrong.  Sigh.  

What features are you using for your equate alignment?  You should use features that can be measured from both orientations.  Can you share a sketch or picture of your part in the two orientations you need to place it in?

Here it is.  I'm using the same two features for my equate alignment as my initial manual alignment.  The outer casting surface and the inner bore, 4 hits on each as shown.  I did a DCC realignment after each manual alignment, using a machined surface.  I suppose I could only use the second orientation and use a star tip to probe the underside and not bother with the equate alignment.

I see multiple problems.  From the following help page:PC-DMIS Help Center - 2023.1 (hexagonmi.com)

For Equate Alignment to function properly:

• The features referenced in your new alignment must be measured after you move your part.
• Those features must reside in the measurement routine below the commands that are executed in the part's original position and orientation (including the original alignment).
• You should reference all of the features for your new alignment in a single alignment block.
• The new alignment should be fully constrained.

This command works with both regular alignment blocks (START_ALIGN/END_ALIGN pairs) and external recalled alignments. The external alignment must be recalled using the RECALL/ALIGNMENT, EXTERNAL command before it becomes available for use in the dialog box.

1) If you're only using a plane and a circle/cylinder then your alignment is not fully constrained, it needs an additional feature to control rotation.

2) Using a cast surface as your LEVEL is likely to introduce a considerable amount of error, depending on the surface texture, flatness and parallelism to the machine faces.

Thanks.  I could mount it on risers in the first orientation and probe the outer machined surface underneath instead.  However, I can't constrain the rotation about Z (the axis of the center bore) because there is no feature to use.  The part is the same no matter how it's rotated.  I suppose I could try taking a point on one of the fins.  But if an equate alignment won't work here, I guess I'll have to rethink how I'm going to do this.

I have used a point taken directly up in the Y axis to control round parts without a rotate datum. I have found it helps the Demon knowing that nothing should be spinning. Any GD&T will just ignore it so it later. 

I have used a point taken directly up in the Y axis to control round parts without a rotate datum. I have found it helps the Demon knowing that nothing should be spinning. Any GD&T will just ignore it so it later.