How to interpret GD&T into tolerance stuck-up analyze base on ISO standard?

[alindragan]

I have a rectangular block, with the width of 100+/-1 mm and one side face of the block is datum A
and the opposite face I have an tolerance frame that indicate parallelism with A within 0.2.

The question is which is the biggest width of the block 101,2 or 101?

Could anyone make reference to a standard?

 

[KENAT]

forum1103 is probably a better place for this kind of question.

You need to tell us what drawing/GD&T standard you are working to (ASME, ISO other...) and if the envelope principle is in force.

Posting guidelines faq731-376

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[alindragan]

The drawing/GD&T standard is based on ISO.

 

[KENAT]

So presumably you aren't invoking envelope principle?

This has been discussed over in forum1103 but I'm having trouble finding a simple example/answer for you.

Posting guidelines faq731-376

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(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[desertfox]

Hi alinragan

I would say 101.2 including the parallel tolerance.

 

[alindragan]

Hi desertfox,

I had the same opinion with you till few weeks ago when I started to play with CETOL6σ and
I saw that the parallelism is not consider for calculation of block width.

And I start to think that this might be true (CETOL6 σ approach)
because if the maximum width of the block would be 101,2 than the condition 100+/-1 would not be respected any more.

 

[desertfox]

Hi

Funny just after I posted I thought the same thing, similarly the same would apply for the minimum size too.
Theredfore the only conclusion can be the parallelism as to fall within the 99 to 101 dimension which seems reasonable.

desertfox

 

[KENAT]

alindragan & desertfox, I think this comes down to the whole envelope principle or "Principle of independency" - which is why I asked about it.

If envelope principle is invoked (default condition in ASME Y14.5 but not ISO) then the 'form' variation of the parallelism has to be within the size tolerance.

If this principle is not invoked than as I understand it the separate form tolerance becomes cumulative with the size tolerance but I'd be lying If I said I was 100% confident which is why I suggested that other forum.

I believe ISO 8015 is the relevant spec - a quick Google found an older copy of dubious copyright so I won't post a link but did crib this text:

4 Principle of independency
Each specified dimensional or geometrical requirement on a drawing shall be met independently, unless a
particular relationship is specified.
Therefore, where no relationship is specified, the geometrical tolerance applies regardless of feature size,
and the two requirements are treated as being unrelated.
Consequently, if a particular relationship of
— size and form, or
— size and orientation, or
— size and location
is required, it shall be specified on the drawing (see clause 6).

6 Mutual dependency of size and geometry
Mutual dependency of size and geometry may be called for by
— the envelope requirement (see 6.1);
— the maximum material principle (see 6.2).
6.1 Envelope requirement
For a single feature, either a cylindrical surface or a feature established by two parallel plane surfaces
(feature of size), the envelope requirement may be applied. The requirement means that the envelope of
perfect form at maximum material size of the feature shall not be violated.
The envelope requirement may be indicated either
— by the symbol <'E' in a circle> placed after the linear tolerance [see Figure 3a)], or
— by reference to an appropriate standard which invokes the envelope requirement.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[desertfox]

Hi Kenat

Thanks for that, I will have a look at the ISO standard and post later

 

[desertfox]

Hi

I can't find anything about the envelope clause, it might help if the OP can confirm which ISO standard, I have access to ISO 1101

 

[alindragan]

Back from vacation…

KENAT is referring to ISO 8015 from 1985,
but this is obsolete and replaced with a new version from 2011.

Any how the bought standards are saying the same think regarding independence principle.

I have a look over this standard/independence principle and, this makes me believe that the answer to my question is 151.2.

But I am not sure about this, and seem not logic, an additional constrain (parallelism) instead of reducing variation of the part is increasing this.

 

[desertfox]

What is 151.2.? and what does it say?

 

[alindragan]

On my first post I have attached a picture with a problem.

 

[desertfox]

I wanted to know what this said per your quote:-

"I have a look over this standard/independence principle and, this makes me believe that the answer to my question is 151.2." what is 151.2 I cannot find it.

 

[alindragan]

See the attachement, I would like to know how to consider the real dimension of the rectangular part in worst case?

I don't know if in reality in worst case the part look like in case one or two?

Based on the discustion that we had I am 90% that the corect worst case is two so the dimension of part is 151,2.

I consider this beeing important, imagine that you have a stack of 3 rectangular part (like in attachement) side by side
and you want to check the total width of your assembly.

 

[desertfox]

Hi

I see now what 151.2 I thought it was a clause in the spec you were looking at.
Bottom line is, does the 151.2 dimension prevent assembly or function? if not I would live with it.
If it does interfere with assembly or function alter either the dimension or the parallel tolerance to suit your needs.
For the record I've always interpreted the tolerance's as we first discussed.

 

[desertfox]

hi

I think this answers your question:-

5.5 Independency principle
By default, every GPS specification for a feature or relation between features shall be fulfilled independent of
other specifications except when it is stated in a standard or by special indication (e.g. Ⓜ modifiers according
to ISO 2692, CZ according to ISO 1101 or Ⓔ modifiers according to ISO 14405-1) as part of the actual
specification.

You can find this on page 4 of ISO 8015 2011, so unless the symbol E in a circle is found our initial interpretation was correct.

 

[CheckerHater]

151 with envelope requirement, 151.2 without envelope requirement.
I faked my own rectangular piece with different dimensions and large tolerances for clarity: