ISO Standards Not Recodnizing Rule #1
ISO Standards Not Recodnizing Rule #1
(OP)
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?
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





RE: ISO Standards Not Recodnizing Rule #1
RE: ISO Standards Not Recodnizing Rule #1
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.
RE: ISO Standards Not Recodnizing Rule #1
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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RE: ISO Standards Not Recodnizing Rule #1
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
RE: ISO Standards Not Recodnizing Rule #1
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.
www.qmsi.ca
RE: ISO Standards Not Recodnizing Rule #1
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).
RE: ISO Standards Not Recodnizing Rule #1
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
RE: ISO Standards Not Recodnizing Rule #1
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.
RE: ISO Standards Not Recodnizing Rule #1
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/nov2...
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.
RE: ISO Standards Not Recodnizing Rule #1
RE: ISO Standards Not Recodnizing Rule #1
John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: ISO Standards Not Recodnizing Rule #1
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.
www.axymetrix.ca
RE: ISO Standards Not Recodnizing Rule #1
-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.
www.axymetrix.ca
RE: ISO Standards Not Recodnizing Rule #1
Thank you, I have seen the same thing, the "envelope" is the best kept secret in every shop I have worked with!
Frank
RE: ISO Standards Not Recodnizing Rule #1
Thank you, I thought I had seen that you could just place it in the tolerance block before somewhere!
Frank
RE: ISO Standards Not Recodnizing Rule #1
John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: ISO Standards Not Recodnizing Rule #1
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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RE: ISO Standards Not Recodnizing Rule #1
Dave D.
www.qmsi.ca
RE: ISO Standards Not Recodnizing Rule #1
CATIA V5 R20
PC-DMIS 2011 MR1
RE: ISO Standards Not Recodnizing Rule #1
CATIA V5 R20
PC-DMIS 2011 MR1
RE: ISO Standards Not Recodnizing Rule #1
To describe form size, let's take a 3.000 +/- .010 tube with and and ID. We have 3 features of size, OD, ID and length. You may take many readings on the OD and report that it is 2.996 - 3.002 but this is size.
Form size is difficult to check but imagine that the tube has a .013 bend in it and it has an average size of 2.999 (using the values that I have given). We are going to use tool room equipment here so we place the tube on the granite table, zero off the table with your indicator on a height gauge (which is the bottom of the tube) and rotate the tube. Place the indicator in the centre top of the tube and measure the distance from the bottom of the tube. As you rotate the tube, the average (or about there) + the bend to give us a form size of 3.012 (2.999 + .013). That is form size and it is out of specification since it is above the upper tolerance of 3.010.
Is this done on the shop floor on each feature of siz?. Not that I have seen yet Designers put a lot of faith in Rule #1 thinking everyone understands it. They don't.
Dave D.
www.qmsi.ca
RE: ISO Standards Not Recodnizing Rule #1
It sounds like what Dave means by "form size" is equivalent to what Y14.5 calls the "actual mating size". In the tube example, this would be the size of the minimum circumscribed cylinder. The surface plate and indicator setup would give a reasonable estimate of the actual mating size, as long as the magnitude of the bending variation was large compared to the circularity and local size variation.
I agree that the actual mating size is often left unchecked.
Evan Janeshewski
Axymetrix Quality Engineering Inc.
www.axymetrix.ca
RE: ISO Standards Not Recodnizing Rule #1
Could you give me an example how you would check form size in my example noted. Use tool room equipment or a CMM with computer control. I would appreciate seeing the difference in our methods.
Thanks
Dave D.
www.qmsi.ca
RE: ISO Standards Not Recodnizing Rule #1
CATIA V5 R20
PC-DMIS 2011 MR1
RE: ISO Standards Not Recodnizing Rule #1
I'd like to interject here. I believe checking form per rule #1 should be a matter of GO/NO GO. I don't believe the amount of form error should be reported. In your scenario, it seems like a number of actual local size measurements should be made along the length of the tube to ensure they are between the MMC and LMC size, then--if the tube isn't very long--it should be able to pass through a hole 3.010" in diameter (gage quality) that is at least the length of the tube. Shouldn't that suffice if the tube is of reasonable length to justify it (say 6")? If rule #1 is to control the straightness then who cares how much the error really is? Now, if straightness is actually specified then the amount of error probably should be reported but personally I would still lean towards a GO/NO GO if it is specified at MMC.
I do have a question about your post: you mentioned an average size of the tube. Does this value matter? Is there ever a scenario where the functional dimension of any feature of size is its average dimension? I'm genuinely curious. I've worked with many inspectors who insist on reporting average sizes and I have never gotten an answer past "That's just what they want." as to why. An average hole size is still going to be larger than the largest pin that will actually go into it.
To answer your question from a few posts back. I have never seen that kind of reporting done.
John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
RE: ISO Standards Not Recodnizing Rule #1
I realize you only directed this to Evan but I'm going to kick in my method here too:
I would scan the tube using a spiral type path with a pitch determined by the length of the tube. Then I would report the min and max values for the max circumscribed circular diameters, max circumscribed cylindrical diameter, and cylindrical form error. Max circumscribed cylindrical diameter would be you actual mating size and is what you are driving at here, I believe. This doesn't require any additional programming work all when done on a CMM. It does require additional machine time to get full surface coverage on the scan. That must be weighed against the function of the feature and the risk level of the manufacturing method to determine if it is justified.
CATIA V5 R20
PC-DMIS 2011 MR1
RE: ISO Standards Not Recodnizing Rule #1
You are correct that a Go/No-go gauge is better but could you imagine, we would need 3 gauges for a tube. Form derived from Rule #1 does not happen yet many Designers here believe so much in Rule #1 that when they really need it confirmed on a feature they feel Rule #1 would cover it. Placing a FCF on the tube OD with a 0 straightness tolerance at MMC forces one to confirm Rule #1. That, absolutely, will be confirmed.
Frankly, I think the ISO method is better. We do not understand Rule #1 on the shop floor in North America.
DaSalo:
It certainly appears that you have confirmed it but would you also perform this on the length of the tube since it is also a feature of size. The ID is really tough to perform using a CMM if there is any length (can't get in the centre) and one would most definitely have to use a Go gauge of its minimum size. Does it happen? No.
Dave D.
www.qmsi.ca