I am trying to clarify how to evaluate this true position. I have a slot that is positionally toleranced to a planar primary datum, cylindrical secondary datum, and cylindrical tertiary datum. There is a basic angle from the tertiary datum to the center of the slot.

I assume that this position is comprised of (a) how centered the slot is on the secondary datum, and (b) how close to the basic angle the slot is from the tertiary datum.

My question is this: Assume I can measure the error from both (a) and (b). How do I combine that information to obtain my result?

Obviously I will level to A, rotate to C and origin XY to B and Z to A. My coordinate system will be on A, centered on B, and clocked to C. This Position establishes a planar tolerance zone opened up at the basic angle on the print, and I am to check whether or not the midplane of the slot falls in the zone.

This wouldn't be the standard 2D/3D Cartesian 2*sqrt(dx^2 + dy^2 + dz^2) nor is it the 2D polar 2*sqrt(r^2 + r0^2 - 2rr0cos(dA)) true position formula....

Position.jpg

I assume that this position is comprised of (a) how centered the slot is on the secondary datum, and (b) how close to the basic angle the slot is from the tertiary datum.

My question is this: Assume I can measure the error from both (a) and (b). How do I combine that information to obtain my result?

Obviously I will level to A, rotate to C and origin XY to B and Z to A. My coordinate system will be on A, centered on B, and clocked to C. This Position establishes a planar tolerance zone opened up at the basic angle on the print, and I am to check whether or not the midplane of the slot falls in the zone.

This wouldn't be the standard 2D/3D Cartesian 2*sqrt(dx^2 + dy^2 + dz^2) nor is it the 2D polar 2*sqrt(r^2 + r0^2 - 2rr0cos(dA)) true position formula....

Position.jpg

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