ISO-ASME Cylindricity vs Positional

[weavedreamer]

I have a Dia 10 -0.005 -0.011 bar with several grooves interupting the diameter. The ISO callout suppliments this with Cylindricity 0.004 and Circularity 0.004. There is also a g5 after the dimension.

The confusion comes in trying to determine the virtual condition envelope. ASME Rule #1,¶2.7.1. yeilds a Dia 9.995

http://www.eng-tips.com/viewthread.cfm?qid=176019&page=20

points out that one of the ISO/ASME differences is the envelope interpretation. How does one generate the virtual condition envelope within the ISO guidelines?

Thanks.

 

[ctopher]

Can you please clarify the dim "Dia 10 -0.005 -0.011" ?
Is it "DIA 10" with a tol of "-0.005 -0.011"?

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[weavedreamer]

Yes, the Dia 10 with a tolerance of -0.005 and -0.011 applied. (effectively 9.995 to 9.989 diameter)

 

[powerhound]

According to the ASME standard, your outer boundary is 9.995 and no element of the feature may violate this boundary. This is where rule #1 comes into play. If you produce this part at 9.995, then your straightness, circularity, and cylindricity must be perfect and as you depart from 9.995 towards 9.989 you gain that error in form by and equal amount. For example, if you produce the pin at 9.990 then you can have straightness error of .005. At 9.991 that error allowance is reduced to .004.
I think the biggest difference between the two standards is that while the ASME standard uses a general rule to control the form of a feature by default, the ISO standard requires that you either put the E with a circle around it to invoke the envelope principle which is like rule #1 OR you must specifically control the form of the feature using form controls. The interpretation is the same but it's the fact that ISO doesn't default to the envelope principle like ASME does that makes the difference.

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[TheTick]

It seems redundant to have circularity value equal to cylindricity value. Is that correct?

 

[powerhound]

Yes it is redundant.

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[weavedreamer]

Agreed on the redundancy. Just stating what is on the print received.

Powerhound, I have a pretty good grasp of the ASME interpretation. You state it well as you usually do.

What I don't understand is the ISO intent. Since there are two form controls assigned to the diameter and the circled e is not present - is the ISO form control bound by the Dia. 9.995 Virtual Condition Envelope, or is the Envelope modified by the stated form controls?

 

[powerhound]

Since the form controls are a refinement of the size tolerance, I would say that the cylindricity is what you should adhere to being that circularity wouldn't address straightness. Being that the envelope principle is not invoked, I don't think the ISO equivalent of "perfect form at MMC" would apply. I have a basic knowledge of ISO so I welcome any correction offered.

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[weavedreamer]

Having an actual Dia. 9.995 part, ASME would call for a 9.995 Dia gage.

Since the drawing references ISO, would the ISO gage be 9.995 dia as well, or does the Cylindricity get added into the equation for a 9.999 dia gage?

 

[powerhound]

That is the dilemma. We need an ISO expert to answer that question.


HELLLOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO...any ISO guys out there?

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