How to setup datum ABC from my sketch?

Hello all.

I am working on a seat structure and try to figure out how to setup datum ABC: Datum A consists of 2 surfaces around 2 circle or round slot A1, A2, both on one side. B consists of 2 circle or round slot B1 B2, on each side of structure.

Since the whole part could rotate around B1-B2, so the C is 2 points C1 and C2 with dimensions. I am not sure how I should choose the level: 1, level on datum A and rotate B1 to C1, but could have issues with B1 and B2.

2. level B1-B2, rotate (B1+B2)/2 to (C1+C2)/2. Transfer to A and B1? I like to second one, but not sure what is the right solution.

Thank you

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0 vpt.se 5 months ago

A and B controls the same axis? What does the FCF rectangles look like on the drawing? A/B/C? C/A/B?
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0 RobOntario 5 months ago in reply to vpt.se

Thank you. A is a surface. Bs are holes on each side of the part. This is a frame of a car seat, which we could fold down, Both rectangles are side views, one from left and the other from right.
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0 WilliamL 5 months ago in reply to RobOntario

He was curious about the FCF on the dimensions I believe. Is it like a Position to ABC or CAB on the GD&T callout, I am too now kinda.
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0 WilliamL 5 months ago in reply to RobOntario

He was curious about the FCF on the dimensions I believe. Is it like a Position to ABC or CAB on the GD&T callout, I am too now kinda.
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0 RobOntario 5 months ago in reply to WilliamL

Ok, I see. Nothing on B1 and B2, ABC on T1
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0 NBO CMM 5 months ago in reply to RobOntario

Regardless of the FCF the Datums as defined over constrain the part. I have had the same issue myself, use a functional approach, Level Y axis through B1 and B2 and origin X and Z, next rotate about Y axis to C midpoint then find the "highest Y" point out of all the A points and set Y origin. Create whatever DATDEF 's you need for the FCF but you will need and do the GD&T to current alignment
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