Alignment/Planare Rotation

[[Fl...]]

Hello,

I have a questions regarding with the alignment for this part. I have the plane A, Circle B , not is a problem, but for rotation is OK to use the line from this two circle (green line) and after for true position i put in the programTP raported directly to Cercle B, is correct?
Another option is : constructed the line from Cercle B and Cercle C and after rotated the sisitem with angle necessary
Is another option ?
Thank's

1.png

[[Ma...]]

I am not sure, but you can use just one circle and rotate it to nominal X or Y ( depends on fixture ), or it is like pattern.
It's useless to use 3d line.

I would consider start alignment to get circle C position accurately

[[Er...]]

For a base aligment I would make it...

Spatial-A
Planar-C
X-B
Y-B
Z-A

No constructions needed. That is just for finding the part to measure it. You could add a distance rotation to square the part like the print.

For measurement I would create a line from -C- to the circle "above" it and use the line as planar, your green line. When I have tried to use this setup in a base alignment repeatability has become an issue. This was due to the holes not being repeatable. And that causes everything to "move" randomly.

[[Fl...]]

Thank's for answer .I understand but not very well . In this moment i use the alignment :
Spatial-A
Planar-green line
X-B
Y-B
Z-A
After i put in the program ,without base alignment , directly TP 0.25 B,see photos.

2.png

[[To...]]

Doesn't Datum C consist of 3 features? If so, keep your base alignment as is. Then, do Best Fit Bore pattern of (3) Datum C Features, allowing translation and rotation (View MMC/LMB of References). This will create a Best Fit Alignment equal to ABC for other characteristics requiring ABC

[[Ro...]]

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Just to add: It should be Best Fit with rotation only allowed. Datum -B- constrains the X-Y translational DOF. Only by using View Tolerance can you get the MMB from Datum -B- and allow translation. You have to make sure -B- is selected as the secondary datum.