Using Constraint for Perpendicularity

[[Li...]]

I good handful of our parts have Perpendicularity callouts.  Either an OD cylinder or ID cylinder to a face/plane.  

We mostly run to a .0005" tolerance.  What is happening when I use Constraint and use the OD or ID to that face or plane it needs to be held to?

I always see and reduction in the actual deviation.  So if it is slightly out, let's say .00055" when go to evaluation and use Constraint and plug in the features it will reduce by .0002-.0003" making that result in spec and look great.  I'm passing out of spec parts by doing this?  There are certain situation when I can manually verify the part on a surface plate and other equipment. This has been working for me.  Seeing manual check data and CMM, meaning they are pretty close to the same result. 

 

Just wondering what "Constraint" is doing. 

[[Ma...]]

Using constraints is forcing that feature to nominal values instead of actuals.

So depending on alignment and actuals of features you can gain better or worse results.

You should avoid this on simple checks like perpendicularity and paralelism.