Composite Position / Best Fit settings

[[Ni...]]

Hi,

I have a part that has 5 different ODs in a circular pattern. There is a composite true position call out for those 5 ODs to Datum B which is a face that is perpendicular to those 5 ODs.

I know i have to make a best fit in the true position characteristic. But i am unsure if i should turn on the best fit for rotation and translation?
I have been reading about composite true positions and i believe if there is only 1 Datum, then it should allow rotation and translation.
If there is 2 Datums, then it should allow only translation, cant rotate anymore.

But in calypso, I dont know if they should be checked or unchecked and i get different results based on that so i would like to know what the correct setting is to have them in.

After trying a lot of different things, i noticed that when rotation and translation are not checked, the X and Y values match very closely to what the basics are using caliper distance. Which makes it easier to see what direction the offsets should be in.
Once both are checked, the results are lower but the X and Y values no longer match what the basics are using caliper distance.

Thank You,
Nixon Uruchima

[[Ma...]]

Using translation and/or rotation depends on elements used as base.
Here you have plane - so it can rotate and move - so check both ( checked means "use it" )

Down there is button "Calculate now" - this will give you BF difference.
I am not sure what are you reporting with caliper distance, since this is composite - so every element have to match it's tolerance.
You would need caliper distance between elements and not center point of BA

[[No...]]

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It depends on how many degrees of freedom each datum restricts. If nothing else is specified, each datum takes as much DOF as it can get. B restricts two rotational and one translational DOF, so it leaves one rotational for the best fit. It also doesn't restrict the XY translation (that's what D would do), so you can use both, translation and rotation..