Best Fit Alignment - Rotating but Not Translating

[Ahb723]

I am having an issue with a best fit rotation about Z, with translation in X and Y.
The program seems to be rotating in Z, possibly translating in Y, but is not translating in X.

I have already done a 2D progressive alignment (leveled to a Z plane, rotated about a X plane, and then translated the origin to the center of a cylinder).
The reason for the best fit alignment is that the x plane is not consistently in the same place, or square to the center of the part.
There is a profile "in the center" of the cylinder that is the actual feature being measured.
I would like to ensure the origin is in the center of the profile, and rotated to match the CAD model to the physical part.

Is there a particular trick or something that I am missing as to why the best fit alignment isn't translating in X (and possibly in Y)?

Thank you and best regards,

Ahb723

[Ego Murphy]

Best Fit "translates" differently than regular Origin: it automatically includes nominal offets to maintain the same nominals as the bestly-fitted features had in the previous coordinate system.

Example: picture a block that's supposed to be 1" wide, but the factory made it 1.25" wide.
Beep 1 point on left of block, set as Origin.
Beep a 2nd point on right side of block, dimension Location and see that this point is deviation result +.25" from nominal - and of course the left point has zero deviation, being the origin and all.
Now do a 2D Best Fit, using both points. Notice that the trihedron does NOT move to be in the middle of the points, but jumps a bit to the right - and when you make new Location dimensions for both points you see they are now showing deviation results like so: lefty is -.125" and righty is +.125". It equally shared the deviation between the two points.

To Sum, "Best Fit" means "make a new coordinate system that gets these features actuals as close as possible to their nominals, equally sharing the deviation, but don't move the nominals."

[Ahb723]

Thank you for the explanation of how a "Best Fit" alignment works. It is certainly much clearer now.

However, I am going to need to translate the origin in the X direction so that it is in the center of the part, to make the profile usable.
If "Best Fit" isn't the correct alignment function to use, what would be? Iterative?

[Ahb723]

Thank you for the explanation of how a "Best Fit" alignment works. It is certainly much clearer now.

However, I am going to need to translate the origin in the X direction so that it is in the center of the part, to make the profile usable.
If "Best Fit" isn't the correct alignment function to use, what would be? Iterative?