The Invocation Principle - Good or Bad?

[CheckerHater]

For all the ISO - lovers out there I introduce new beating horse - The Invocation Principle.

According to 2011 edition of ISO 8015 which is now regarded as "fundamental GPS standard",
"Once a portion of the ISO GPS system is invoked in a mechanical engineering product documentation, the entire ISO GPS system is invoked, unless otherwise indicated on the documentation".

From now on "The most common way to invoke the ISO GPS system is to use one or more GPS specifications in a drawing".

The opinions on the matter are split really wide.
Some believe that any self-respecting company already has either ISO or ANSI/ASME specified in the title block or tolerance note, so the new rule will not change their way of doing business even a tiny bit.
The others are afraid, that as soon you make simple sketch on the piece of wrapping paper and scribe something that looks like GD&T symbol that "coincidentally" looks the same in both systems, the ISO will immediately take over your sketch (all the 5 5-inch binders will apply).

I am sure Eng-Tips' Dimensioning and tolerancing community will have some strong opinions, but still hope an agreement can be reached.

 

[pmarc]

CH,
I already had some discussions about it with some people and it is just like you said - the opinions are extremely different.

From Y14.5 user perspective, I do not see a problem as long as a print explicitly states that it follows Y14.5-xxxx standard. I can't imagine that someone who sees a note like: "DIMENSIONING AND TOLERANCING ACCORDING TO ASME Y14.5-2009" will even think of invoking ISO GPS standards to the print.

The other side of the story is when such reference is missing. And this is what bothers ASME guys the most. They cannot understand why ISO claims that their rules are superior over other national standards like US one. Maybe the reason is that ISO is an international organization while ASME is only a national committee... it is just my guess.

 

[CheckerHater]

There is a difference between "superior" and "default".

It may be a good thing if targeting people / companies who are either too lazy to put their paperwork in order, are ignorant of standards, or chose to "seat between two chairs", or simply trying to ignore standards they "don't like".

Imagine small American company having partners, suppliers, customers scattered between some dozen countries (all ISO members).
One day supplier gets the drawing without projection angle specified, and guess what?
Somebody gets mirror image of the part they expected (true story).

If this is an effort to make everyone to clean their act in today's transparent world, so be it.

 

[pmarc]

If this company gets mirror image of the part, I am saying it is only their fault, because the drawing was incomplete - it did not specify projection angle.

If I want to get a component painted in black from my supplier, I cannot expect to receive it if my drawing does not say anything about black color. The contract between me and my supplier specifies that the supplier is obliged to be able to read technical documentation, not to read in my mind.

 

[MintJulep]

Once a portion of the ISO GPS system is invoked in a mechanical engineering product documentation, the entire ISO GPS system is invoked, unless otherwise indicated on the documentation

Sounds like drawing title blocks need to dedicate some space to two new check-boxes. And designers actually need to pay attention to which one they check.

[] This drawing in full compliance with ISO 8015.

[] This drawing utilizes symbology and dimensioning practices in line with ISO 8015 for convenience only. The use of ISO 8015 practices on this drawing does not invoke full compliance with ISO 8015

That should clarify things perfectly

 

[CheckerHater]

To pmarc:

I agree it's customers fault - they sent out something more like sketch than well-developed drawing.
Supplier is getting prints from all over the world.
ISO has 161 member countries.
Only 1 of them is using Third-angle projection.
Wouldn't you actually give the guys the benefit of a doubt?
How to stop the flow of inferior drawings? Create the awareness that they may be interpreted the wrong way.

 

[KENAT]

Interesting. Some of the less well known iso stds have aspects that many might not want to invoke by default.

For instance the oft maligned iso 2768.

In fact, doesn't the invocation principle explicitly conflict with what 2768 says about how to invoke it?

Posting guidelines faq731-376

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

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

 

[CheckerHater]

To kenat:
It' quite interesting: ISO 2768 is considered "complementary" standard.
The rules in complementary standards can override rules in Fundamental and Global standards.
So if 2768 says you have to explicitly specify it on the drawing, then you cannot invoke it atomatically.
Sleping better tonight?

 

[KENAT]

Well, I wasn't losing sleep but that's an interesting clarification not present in the OP, thanks CH.

Posting guidelines faq731-376

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

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

 

[MechNorth]

This discussion has come up within ASME, and they are addressing it, though I haven't heard any details on their response for a while now. Needless to say, there are a lot of legal implications that need to be sorted out.

I emphasize to my classes that they must specify a standard on the drawing or else the downstream user can interpret it however they wish. I usually get some smart-ass comments like "who cares, they'll just have to eat the cost of re-making the piece". My comment is that it inevitably means that the company that supplied the drawing will be paying a much heavier price in the long run as the supplier jacks up the prices on everything down the line to recoup their losses. And, I mention that companies have started to hold engineers personally responsible for such messes; they don't have to pay for the losses, but they do pay with their jobs.



Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[fsincox]

CH,
That makes sense to me,too, The tolerance grade needs to be specified as stated in the standard, there is no default tolerance grade, unless otherwise specified as I recall?
frank

 

[fcsuper]

The problem with invoking a standard without stating that you are invoking it is the legel issue of which standard is being invoked. If a drawing was made in 1999, but revised in 2012, and stated no standard at either time, does the standards applicable in 1999 apply, or does 2012 apply? What is the drawing also didn't state a date of inception? Also, ISO isn't a legal entity, so they really cannot make the claim that technical drawing falls under their rules. In fact, in a free country, there is no way to enforce that 100%, even with significant market pressure.

I think it's an attempt to make it easy on existing customers of ISO, but doesn't really impact companies that don't adhere to standards. It also doesn't really protect ISO customers since it is still up to the customer to clearly lay out the terms of the purchase with their vendor. The vendor isn't under contract with ISO directly, so if the customer doesn't make a statement either way, it's still on them if the vendor doesn't interpret the drawing according to ISO.

If ISO established some sort of certification in this area, then certified vendors could be held accountable.

Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion