Determining Virtual Condition using ISO Composite Callout

[weavedreamer]

Does the Parallelism or the Straightness get subtracted from the minimum diameter to establish the virtual condition of the illustrated cylinder? The envelope principle is not specified / invoked in this case.

Attachment should be the same as inline image, for those who can view the inline image.

 

[greenimi]

Can you even establish a virtcual virtual condition from only "form controls"?

How should I read the parallelism callout? Is it legal "as shown" callout in ISO GPS? What is the interepretation of the parallelism callout: "the extracted median line shall be contained between two parallel planes 0.0025 apart, which are parallel to datum A" , which is datum A?
I am very confused.

 

[weavedreamer]

Datum A was described as the opposite side of the cylinder from where the Parallelism is being measured. (Line of contact?)
As such, it (the Parallelism) assumes the role of an orientation control?
The confusion is shared here.

 

[greenimi]

In general in ASME (not in ISO) a datum is driven from a datum feature. I suspect the same concept is in ISO GPS. I don't have ISO 5459 in front of me, but as far as I remember it is almost the same concept.
So, my question is: what is the datum feature that drives your datum?
Maybe ask the designer.

Not sure:"Datum A was described as the opposite side of the cylinder from where the Parallelism is being measured." make any sense at least per my limited experience in ISO GPS

 

[weavedreamer]

The diameter 6.0055/6.0030 is identified as a feature of size Datum H. Datum A is shown on the leader line opposite where the parallelism is called off. So far, it is a hearsay verbal explanation of what the drawing is "supposed" to mean.

Instead of "What is the Virtual Condition?", the question that need be answered first then would be "Is this a legitimate callout?"

 

[SeasonLee]

Its a line contact as shown, I am anxious to know when and where to use a line as datum feature in ISO GPS.

Season

 

[weavedreamer]

There is allowance for a Datum Target Line in ISO GPS.

This would be an example of a static case.
The callout being inquired about is described as a dynamic case.

 

[CheckerHater]

This way of applying parallelism was meant for cylinder generating lines.

Is considered "former practice" for at least 20 years

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[weavedreamer]

CheckerHater,
You write "former practice" — as in established by precedence, or indicating an obsolete and archaic usage?

 

[CheckerHater]

Obsolete.
No longer used due to being ambiguous, like placing datum feature symbol on the center line.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[greenimi]

CH,
Somehow unrelated question: If a drawing states only ISO GPS (let's say ISO 8015 or Form and Pos. tol DIN ISO 1101) how do you know which version or revision is applicable?

 

[CheckerHater]

If a drawing states only ISO GPS (let's say ISO 8015 or Form and Pos. tol DIN ISO 1101) how do you know which version or revision is applicable?

I believe this is one of technicalities that isn't fully resolved yet.
If date is not specified, the latest version is implied, which eventually will create problems, as the content of the standards is changing, especially recently.
Sorry cannot provide direct reference to the standard right now

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[weavedreamer]

So, as it is spelled out here, the callout is obsolete, so it is not likely a legitimate callout as it is a recent vintage drawing.

For pragmatic purposes, in order to provide a V.C. value to work with, it equates to 6.003-0.0025=6.0005 V.C. per archaic interpretation, with the parallelism being used as the orientation control to the opposing side of the cylinder (with appropriate caveats stated).

Thanks greenimi, SeasonLee, and CheckerHater for chiming in.