Different True Position Callout

[[Za...]]

Hello, I have a question regarding a GD&T True Position callout on a part I'm programming...
Is there a difference between the callout above and the one below? If so, what is the difference? and how would I program this as compared to the one below?

[[Aa...]]

That depends on what kind of geometric features A and B are, and how they are positioned an oriented relative to one another. In A|B, there's a primary and secondary datum derived from A and B, respectively. In A-B, there's only one datum, which is derived from both A and B.

[[Mi...]]

The big difference is your tolerance zone is diametrical with that symbol on the first DRF (Ø)

Think of it like a straw that your points should lie

[[Za...]]

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A and B are both planes. A is my +Z plane and B is my -Y plane. I just want to make sure that this is the correct way to program it.

[[Za...]]

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How would that differ from the one that reads [A-B]? Most of the True Position callouts that I've seen so far have been [A|B|C] and I just select the feature I want to get the True Position of then my datum features. I just want to make sure this is programmed correctly before I send the results out to the appropriate parties. I'm fairly new to programming and I've had to learn this stuff on the fly since our last CMM programmer left. My company is eventually going to send me to the advanced Calypso training (already took the beginner course), but I don't know how long that's going to take to happen. I'm just trying to get through for the time being.

[[Aa...]]

It seems bizarre to me to have a multiple datum feature of two perpendicular planes (not features of size). Are you sure A and B aren't the widths in those directions?

Since the two positions are both applied to a cylinder, the one that doesn't spell out a cylindrical tolerance zone would need to be a "bi-directional" position tolerance, meaning they should have spelled out the direction the tolerance is applied.

My guess is that what they meant is that it's in the direction perpendicular to the B datum, since the DRF should have full mobility in the other direction. It's not a correct application of Y14.5, but I think that's what they mean. Datum C probably arrests movement in your X-direction.

[[sh...]]

Capture.JPGCapture.JPGCapture.JPG

[[SH...]]

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As far as continuous feature is concerned, either it should be in a same plane or a same axis. But you are telling both are mutually perpendicular to each other, it look like a wired drawing. Your first DRF control only orientation that means,the cylinder should be parallel to datum A ,in your second DRF in addition to above the cylinder axis origin at datum B. The method you calculated the position is correct, I think problem in your drawing....

[[An...]]

Legal?
Not legal?
I don't know.
See attached.

Contribution_03_10_2019.pdf

[[Aa...]]

I'm not sure that A-B (with perpendicular planes) is illegal, but I would still argue that it's bad practice. It leaves a lot of potential for datum instability, if the angle between them is not exactly 90 degrees. Setting that instability aside, A-B clearly arrests three rotational and two translational degrees of freedom, leaving unlimited DRF mobility in the direction parallel to the edge between the two faces (in this case, along the X-direction). So, for the .12 position FCF I would say what you have is right, but you need to switch the "Shape of Zone" to "Y Only". That is, unless the intent was for a cylindrical tolerance zone--the "straw" as Mike put it. Had they not omitted the diameter symbol from the 0.12 position FCF, the axis would have to fit within said "straw", which could move in the X direction, but not rotate. You could simulate this by creating a best fit alignment from your hole allowing translation in X only, and tying your FCF to that alignment, diametrical XY.