Best fit pattern

[Jay_Q]

I’m using legacy dimensioning and have a question about best fit. To keep it simple, if I have a 4 hole pattern to datum A|B. A being the plane the pattern is on and B being a hole in the center of the 4 hole pattern. What is the proper best fit alignment for a A|B datum scheme? I normally would pick up the pattern by using one of the holes as a “C” datum for rotation so I get good hits. Recall that alignment with origin on A|B. Then 2d best fit min/max rotate and translate. Is rotate AND translate right? Or does rotate and translate only give me the deviation from the pattern to its self. Even if I am origin on A|B. The numbers look like they are coming from the center of B. But I was concerned it was “cheating”

[AndersI]

As you have a B datum locking the origin, you may only 2D rotate in the best fit of the pattern.

[NinjaBadger]

Rotate only.

If you translate and rotate you are shifting off of Datum B

[Jay_Q]

Ok. Thanks guys! So is that really any different then rotating B to one of the holes?

[NinjaBadger]

Yes, it will minimize the average error (in simplistic terms)

[Jay_Q]

Ok. Thanks for clearing that up. I asked that same question when I was in class through hexagon and they told me best fit rotate and translate was correct. But the more I was reading about it, it didn’t seem right.