TP A-B

[[Da...]]

Is this TP callout legal?

tp111.pdftp.zip

[[Cl...]]

I think so. Without A how do you clock the part?

[[Da...]]

What bothers me is why is given like |A-B| and not |A|B|

[[Cl...]]

Based on the fact that nowhere on the ASME Y 14.5 chart does it show two, or more datums that are not drawn as AIB (not A-B), I would say it's just drawn incorrectly.

[[Za...]]

ASME 14.5m-2009

4.12.2 Single Axis of Two Coaxial features of Size

.....of a single datum axis established from the axes of the datum feature simulators that constrain the two coaxial diameters simultaneously....

two coaxial diameters A-B

I'm apt to say it only applies when the datum features lay on common center-line relative to the features center-line. Which the features on the attached drawing are not.

[[Cl...]]

Thanks Zach, I learn something new everyday.

[[De...]]

Pretty sure this is legal. This is a multiple Datum feature.

The following is from Y14.5-2009, Figure 4-22 in the spec shows an example using two planes as a multiple datum feature.

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The difference between A | B and A - B is that using A - B makes both features have equal amount of precedence on the inspection.

If it was written A | B, then A would take precedence and control location and orientation relative to A and B would only control orientation around A.

The way it is shown A and B have equal precedence so the orientation of A and the orientation of B should be balanced during the inspection when determining the orientation of the part prior to taking a measurement - its a subtle distinction but there is a difference.

Where this is likely to make the most difference is if Datum A and or the hole are not parallel to the axis of Datum B.

With all that said the true position of the hole is 0.5 even in metric I would expect that should really not be an issue in either case.

[[Da...]]

So how would you set this up in Calypso? Can it even do multiple datums?

[[Cl...]]

Just a stab in the dark here? Could be wrong. Also, didn't add any plane for Z?

[[De...]]

I haven't had to do this and have not tried it, but the following is what I would try first.

I would create a geometry best fit alignment that included Datum A and Datum B

For the best fit I would allow rotation in all three axes.

I would then create a theoretical cylinder the size of datum B at basic that used the geometry best fit alignment and use that as my primary datum.
I would also create a theoretical 3d line using the geometry best fit alignment that represents a line from the center of Datum B to the center of datum A at basic

Now you can make your true position call out and for your primary you use the cylinder and for secondary you use the line.

Because the line and the cylinder are theoretical and are created with the nominal values equal to the basic values for the part and because they both use the geometry best fit, calypso will first measure the actual features, then perform the best fit to calculate the alignment, the theoretical will be aligned to that alignment so the calculation will be made to the alignment.

Its probably possible to skip the theoretical features all together and just choose the geometry best fit alignment in your true position callout but personally I like to have actual features to use.

[[Ri...]]

You would measure the features individually, and recall the feature points into a Step Cylinder.

[[De...]]

Datum A and Datum B do not share a common axis though. 😕

[[Br...]]

That drawing isn't ASME. That little E symbol next to the size dimension signifies an envelope condition. Its the same as Rule #1 in ASME. But that symbol is only found in ISO. I'm not exactly sure what ISO says about Multiple datum features called out that way. You might look to see what ISO says about it.

[[An...]]

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Sorry,I have to contradict.
The DRF A-B does not include any information about the use of a planar alignment.

Two cylinders that are parallel but not coaxial mean the following:
Symmetry of two cylinders.
Defining two translatory degrees of freedom.
Defining two rotatory degrees of freedom.
The third rotatory degree of freedom is undefined.

The rotatory location of diameter 6 in this drawing is unlimited.

[[De...]]

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I agree with the above with regard to the datum features alone, however there are basic dimensions there as well.

The two cylinders are not on a common axis, and they give basic dimensions referencing the two datum cylinders when they are in line.

The basic dimensions can only be correct when datums A and B are in the correct orientation.

So once they put the hole in with a true position to A - B with the basic dimensions they have essentially locked rotation.

That is how I see it anyhow.

[[An...]]

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Interesting insight.
Any further thoughts?

[[Ri...]]

Ahh...

I guess I should have looked.

Introduced into Calypso is the Parallel Cylinder.

"New feature: Parallel cylinder - Shared datum
according to ISO 5459
According to the ISO standard 5459, certain characteristics that have a
“shared datum” must be checked. A shared datum is defined as two or
more features that are evaluated together without any special order. To
meet this prerequisite, the new feature “Parallel cylinder” has been introduced in CALYPSO. A parallel cylinder is the datum feature for location
tolerances requiring a shared datum. Further adjustments support the
implementation of the standard"

I don't think that is what the drawing wants though.

[[Da...]]

Interesting, thanks all. I can't find a word about GDT standard used on the original drawing, but units are in mm and there is some ISO 6930 referenced. Yes, this is a stamped part. It's even more interesting that is only 0.5 mm thick (ups, I exaggerated on that 3D model).
Sorry I didn't provide all of that info before...

[[Ri...]]

From my Aukom GD&T training, it is stated that if one ISO specification is referenced, then all are applied. It saves from them having to list 20+ standards on the drawing.

Good luck!

[[sh...]]

I agree,this print looks incorrectly drawn. If this part was a cylindrical part the A-B co-axial datum would make sense.
However this is metal stamped part and extremely thin. I would intemperate it as A|B.

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[[Ri...]]

This isn't an ASME print though. It references an ISO specification, so by default it references all ISO specifications. It would have to explicitly state to interpret the GD&T per ASME if that wasn't the case.