ISO Standards Not Recodnizing Rule #1 5

[SpaciouS]

As I understand it, the ISO 1101 Geometric Tolerancing standards do not recodnize Rule #1. How doe this approach work? I'ts hard for me understand since Rule #1 is such an important concept when using the ASME standard.

There is no such thing as perfect form at MMC?

All envelopes are to be looked at in terms of worst-case boundaries?

Thanks,
Sean

 

[pmarc]

ISO approach is based on a philosophy that each geometrical requirement specified on a print is met independently of others. That however does not mean you cannot define a requirement working similar to ASME's Rule #1. Just use E within a circle and associate it with size dimension and that would do the thing.

 

[CheckerHater]

If you want envelope you just specify it on the drawing.
When you specify, say, position MMC it means exactly the same as in ASME.
Very often envelope by default does more harm than good; this is why in 2009 they added independence to Y14.5.
Also very often envelope is not fully understood even in ASME-land.
All together things are not so bad.

 

[dgallup]

I think it's really ISO 8015 - Fundamental Tolerancing Principle, that you have a problem with. This is what states that each specified dimensional or geometrical requirement shall be met independently unless specified otherwise. Mutual dependency of size and geometry may be called for by the envelope requirement (the letter E in a circle) or the maximum material principle (the letter M in a circle). Or you can do what we do and invoke a national standard (like Y14.5) to effect the envelope principle by default even though we use the ISO 1101 GD&T.

If you really want to stay totally ISO then you need to consider every dimension individually and either add a lot circled E's & M's or be prepared to accept a lot of misshapen parts. It is a fundamentally different way of approaching the dimensioning scheme.

We came up with our system when we were sold from one foreign company that had their own drafting standards (common decades ago) to another foreign company of a different nationality. We needed to adopt a set of standards that would not change the interpretation of hundreds of existing drawings.

If you are going to work strictly ISO you probably need to take an ISO training course, they are hard to find in the US, maybe easier if you are somewhere else.

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[Belanger]

Or you can do what we do and invoke a national standard (like Y14.5) to effect the envelope principle by default even though we use the ISO 1101 GD&T.

Not to sidetrack the discussion, but how do you invoke Y14.5 alongside the ISO tolerancing system? Do you have a note saying that both systems apply to the given drawing?

I ask because Y14.5 might give you the envelope principle, but how would a reader interpret a concentricity callout, which has a very different meaning in the two systems?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[dingy2]

Designers seem to think that Rule #1 is widely understood in North American but people on the shop floor and most CMM Operators do not understand nor do they confirm form size.

Every dimension is numbered on the drawing for referencing. If Rule #1 was understood, then each dimension covering a feature of size would need 2 numbers, one for size and one for form size. Does it happen out there? I have never seen it. Maybe other people in this forum do see it.



Dave D.

http://www.qmsi.ca

 

[CheckerHater]

Little bit of nit-picking.
ISO 8015 does not deal with independence principle anymore. This stuff is moved to ISO 14405.
ISO 14405 also tells you that if you don’t like default definition you can specify any other definition next to the title block.
So, there is no need to mark thousands of dimensions with (E).

 

[powerhound]

Dave,

I don't understand what you said about rule #1. Why would every FOS dimension require 2 numbers if someone understood rule #1? Per rule #1 the form dimension is controlled by the size dimension. If it is understood by someone then they would know what amount of form error would be allowable based on the actual size of the FOS. Maybe I just didn't read that right.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[pmarc]

powerhound,
It is not about direct reporting of actual value of form error. It is about reporting whether the envelope requirement has or has not been violated.

Dave, please correct me if I am wrong.

 

[pmarc]

Koda,
Frank and Kenat are right - there is no relationship between the two cylinders defined on your print.
The relationship can be defined by at least half a dozen of methods, depending on what is really required. See the following link as a reference (Subject: Total Runout Question):

http://www.geotolmeadows.com/newsletters/2012/nov2012.htm

A method not mentioned there has been already mentioned by Frank - "2x position to no datum" as shown in fig. 4-24 of Y14.5-2009.

 

[pmarc]

My apologies, this should be posted in the other thread

 

[powerhound]

I'm on board with that, pmarc. I guess since I feel like I understand rule #1, and I don't require 2 dimensions for a single FOS to understand how it applies to a FOS, I don't think I'm getting what Dave is saying.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[axym]

powerhound,

I believe what Dave is saying is that two actual values could/should be reported for a Size tolerance, because there are two distinct requirements (actal local size, and Rule #1 boundary). So there would be one value reported for the extreme actual local size (i.e. 2-point size), and one value for the actual mating size (i.e. envelope size). But this is not commonly seen in industry. Dave, is that right?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[axym]

Just to take Dave's point even further, here's another take on it. Strictly speaking, three different values could be reported for each Size tolerance:

-Largest Actual Local Size
-Smallest Actual Local Size
-Actual Mating Size

I don't think I have ever seen this done in practice, but it could be.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[fsincox]

Dave,
Thank you, I have seen the same thing, the "envelope" is the best kept secret in every shop I have worked with!
Frank

 

[fsincox]

CH,
Thank you, I thought I had seen that you could just place it in the tolerance block before somewhere!
Frank

 

[powerhound]

Thanks Evan. I see now. Dave is referring to dimensions being reported. I was seeing it from the manufacturing side. I thought that he was talking about a manufacturing print with 2 numbers for a FOS.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[dgallup]

Not to sidetrack the discussion, but how do you invoke Y14.5 alongside the ISO tolerancing system? Do you have a note saying that both systems apply to the given drawing?

I ask because Y14.5 might give you the envelope principle, but how would a reader interpret a concentricity callout, which has a very different meaning in the two systems?

Little bit of nit-picking.
ISO 8015 does not deal with independence principle anymore. This stuff is moved to ISO 14405.
ISO 14405 also tells you that if you don’t like default definition you can specify any other definition next to the title block.
So, there is no need to mark thousands of dimensions with (E).

Very simply. We have our own document called out on every drawing that explicitly list every ISO standard we use (including revision date) and any exceptions or stipulations. You have to take an approach like this with ISO because there are so many standards and some of them are mutually exclusive. You can not just say "we observe ISO drafting standards", you have to say which ones. ISO 8015-1985 (the version we reference and use) section 6.1 says you can invoke the envelope principal by reference to a standard that invokes it. We do this in our drawing dimensioning and tolerancing standard.

In most cases we are in full compliance with the ISO standards we use but in some cases there may be exceptions such as ISO 1302-1978 section 4.2.4 we stipulate that any unspecified surface roughness sampling length shall be 0.8 mm. For some reason the authors of that document did not see fit to give a default value.

ISO 14405 is not in my book of ISO standards & we don't invoke it. ISO has a very bad habit of creating conflicting standards. If I had it to do over again I would not use it.

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[dingy2]

Yes, Evan, you are quite correct. Whenever there are sample submissions, a marked up drawing would travel with the samples to the Customer. On the marked up drawing, all dimensions are number for reference. The CMM Operator would have to assign 2 numbers for each dimension relating to a feature of size. The first number is for local size and it should be reported as a range - lowest to highest. The second number would be assigned for form size. Please, anyone, have you seen this done? Ever???

Dave D.

http://www.qmsi.ca

 

[DaSalo]

Not sure I'm 100% clear on what you mean by "form size". Never seen that term used. If you mean actual mating envelope size then yes,I believe I do report that when risk level justifies that volume of data. Please tell me if I'm incorrect. A hole is scanned at several cross sections (number depends on hole length, tolerance, ruby diameter, etc). From this I report minimum inscribed and max circumscribed circle diameters and minimum inscribed cylinder diameter. The later is your actual mating size without taking orientation into account.

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