GD&T (GPS) per ISO 1101, 8015, & 2768 10

[GMIracing]

I realize that this has been discussed here a few times before, but I could use some additional help.

Working for a very global oriented company, we use ISO for all Global Dimensioning and Tolerancing standards for our drawings. After receiving training per the ASME Y14.5 standard, it has been a constant state of confusion for me while trying to understand our standard tolerancing schemes that we have on our prints.

Time and time again I have seen prints that outright conflict with ASME, and most often they lack very important controls, and sometimes datums, to insure proper function of the parts. Every time I question or comment about this, I am always told that our general tolerance callout of ISO 2768 covers anything not stated. Now I have never been trained per ISO and I have had a difficult time finding training, in the US, for the many documents that make up the ISO Geometrical Product Specifications (GPS).

Recently, there has been a push to provide further development to our Design Engineers and Technical Drawers in the area of making and understanding drawings made to the ISO standards. As a result, we have been watching internal training videos on the subject matter. This is where my

While I expected some slight differences, like ISO Concentricity is very similarly used as ASME Position, I was absolutely SHOCKED when I got to the short training video on the „General Tolerances“ portion of ISO 8015 and 2768. I took some screen captures of the example shown by the video. So can any of the experts here tell me their $0.02 on this matter?

Has as anyone here actually been formally trained to the ISO standard? We are starting to really push towards sourcing parts to new suppliers in countries not accustomed to DIN/ISO, and I am not certain that we will all be speaking the same engineering „Language“.

-Ryan

 

[GMIracing]

old threads for crossreference:

"What is the differences between ASME Y14.5M and ISO 1011 ???"

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

"Tolerance analysis ISO2768"

http://www.eng-tips.com/viewthread.cfm?qid=196260

"tolerance analysis to ISO 8015 & 2768 part 1 (again!)"

http://www.eng-tips.com/viewthread.cfm?qid=197786

 

[KENAT]

I was toing to reference you to those 2 ISO 2768 threads.

The US vendor of my German supplier even had a local tolerance expert have a look at the implications of 2768 and they agreed with me not the German office so it certainly seems 2768 can cause confusion.

I have real concerns over 2768 but haven't been trained on it or spent enough time on it to get my head round it. To me is almost seems like a standard for lazy designers/engineers who don't want to do the tol analysis and don't really care if things fit together, but that may be unfair.

Sorry, not much of an answer.

KENAT, probably the least qualified checker you'll ever meet...

 

[dgallup]

I'm not familiar with 2768 but I am with 8015 and I don't get what is posted in your ISO_GDT.pdf from 8015 at all. 8015 specifically states that if you need any relationship between size & form or size & orientation or size & location you have to specify it on the drawing. In other words, there is NO envelope principal of implied perfect form at MMC. If you need the envelope requirement you have to put the symbol of the circle with an E inside on each & every feature of size that it applies to. There is only one circle E on the drawing so only the ID has an envelope requirement. Maybe all the rest comes from 2768? I have quite a few books of ISO standards but none of them contain 2768.

8015 is so contrary to the ASME Y14.5 way of doing things that we explicitly call out the following stipulations in our standard for drawings, dimensioning & tolerancing:

ISO 8015: 1985 Technical drawings - Fundamental tolerancing principle
Stipulation: Clause 5.1.1 Linear tolerances: unless otherwise specified on the drawing, the
envelope requirement is invoked for all drawings per ANSI/ASME Y14.5M - 1994.
Stipulation: Clause 6 Mutual dependency of size and geometry: unless otherwise specified on the
drawing, the envelope requirement is invoked for all drawings per ANSI/ASME 14.5M -1994.
Stipulation: Clause 6.1 Envelope requirement: unless otherwise specified on the drawing, the
envelope requirement is invoked for all drawings per ANSI/ASME 14.5M - 1994.
Stipulation: Clause 7.2 Designation: unless otherwise specified on the drawing, the envelope
requirement is invoked for all drawings per ANSI/ASME 14.5M - 1994 from the American National
Standards Institute.

 

[GMIracing]

Thanks for your input KENAT and dgallup, I really appreciate it.

First, you are right dgallup. The training video I watched happened to combined the two standards into one short segement, but I now realize that I obviously misunderstood what they were trying to clarify and to which standard the graphic was refering. The video was in German, and not having mastered the language yet I fear I missed a few vital points. After re-reading the ISO 8015-1985 (E) standard, I think that all of the green „inferred/implied“ datums and GDT controls in my pdf are not implied by 8015, but are actually coming entirely from the 2768-mH. Any chance you might be willing to share the title of the book you find the most useful for ISO GPS?

Also, I find it interersting dgallup that you use so many Stipulations for ISO 8015. The standard is only 5 pages and you have invoked ASME Y14.5M over a majority of the ISO Clauses. Is there any reason you don’t just omit the ISO 8015 and 100% rely on the ASME Y14.5M standard as the default?

Kenat – I think your opinion of this standard is higher than the one I have. I have had the pleasure of sourcing our standard German designs to suppliers in the NAFTA region and I found myself on the side of each and every supplier than had even the most basic understanding of the ASME standard. The difficult part were the suppliers that quoted that never had any concerns, as it made me realize they likely didn’t perform a true feasibility study for tolerance capabilities.

 

[dgallup]

When we wrote our standard we were changing from British to French ownership. Our British owners had their own set of standards that we could no longer use. We wanted to use 100% ISO standards but had to very carefully choose how we implemented them so that the interpretation of the drawings would not be affected. We did not want to have to review thousands of drawing & redo the dimensioning. We used the loophole in 8015 that allows stipulating a local standard. I don't think you can exclude 8015 altogether in an ISO system as too many other specs reference it. Oh the complicated web we weave.

 

[KENAT]

GMI, if you'd posted this 6 months ago I'd have had a bit more venom but it's worn off over time. I still think that the last paragraph of the standard basically tells you the standard is meaningless but others disagree.

Now using this standard to answer the old old question of 'what are typicaly machining tolerances' and then puttin that on the drawing (where it suits function etc), maybe but invoking it complete as is, not if I can help it.

KENAT, probably the least qualified checker you'll ever meet...

 

[Brandy7]

(Note:ISO 8015 Canceled & Replaced by ISO 286-1 1988)

BEST BOOK TO STUDY DIFFERENCES-WELL WORTH TIME AND $$$


GEOMETRIC DIMENSIONING AND TOLERANCING IN 2007
Workbook and Answerbook
by James D. Meadows]

560 pages, illustrated / $109.00
ISBN: 0-9714401-2-3

This is the most comprehensive GD&T textbook ever written by a single author. Geometric Dimensioning and Tolerancing in 2007 has the unprecedented ability to cover almost every facet of tolerancing. Unlike any before it, this GD&T textbook, and the course based on it, can cover all the tolerancing-related topics time allows. Time is your only limiting factor in topics to be covered in a workshop. . . but the textbook has it all!

Although based on the rules found in the ASME Y14.5 standard, it also covers topics from other recently published standards by ASME not found in older texts. It includes step-by-step procedures for dimensioning and tolerancing parts and assemblies. It shows how to analyze the tolerances applied using both worst case and statistical analysis. This book demonstrates the connection between the application of functional geometric tolerances and its effect on manufacturability and inspection, stressing optimal ways to achieve a high-quality product at the lowest possible cost to the customer.

Chapter 1–Geometric Dimensioning and Tolerancing
Symbology, Rules and Formulas; GD&T–an Introduction

Chapter 2 – Selecting a Tolerancing Approach
Datums and Datum Features; Steps in a Tolerancing Scheme; How to Read a Feature Control Frame

Chapter 3 – True Geometric Counterparts
True Geometric Counterparts and Datum Feature Simulators; Fixtures, Gages and Virtual Condition Boundaries

Chapter 4 – Boundaries and Material Condition symbols, MMC, LMC & RFS
Geometric Dimensioning and Tolerancing Overview; Material Condition Symbols and the Boundaries they Generate

Chapter 5–Major Concepts of Geometric Dimensioning and Tolerancing
Converting from Plus and Minus to Geometric Tolerancing; Position; Gaging; Flatness; Selecting Datum Features’ Perpendicularity; Mating Part Tolerancing; Reading the Feature Control Frames as a Language; Calculating Inner and Outer Boundaries [virtual condition, resultant condition]; MMC vs. RFS vs. LMC [what they mean, when to use them, boundaries they create]; Bonus Tolerancing Formulas; Allowed versus Actual Deviation from True Position Calculations; A Difference between Bonus Tolerance (growth) and Datum Shift (movement) of Tolerance Zones

Chapter 6 – Form
Flatness; Straightness; Cylindricity; Circularity

Chapter 7 – Orientation
Overview; Parallelism; Perpendicularity; Angularity; Actual Mating Envelopes; Orientation of Centerplanes

Chapter 8 – Profile
Profile of a Surface; Profile of a Line; Composite Profile; Two Single Segment Profile; Coplanarity; Conicity

Chapter 9 – Runout
Circular Runout; Total Runout

Chapter 10 – Concentricity and Symmetry
Concentricity; Symmetry

Chapter 11 – Datums and Datum Features
More About Datums and Datum Features [How they are Selected; what they Mean]; Specifying Degrees of Freedom; Establishing a Valid Datum [Curved Surfaces as Datum Features, Datum Feature Patterns referenced at MMC or RFS, Conical Datum Features

Chapter 12 – Centerplane Datums
Centerplane Datums—an Overview; Centerplane Datums on Mating Parts

Chapter 13 – Position with Fixed Fastener Assemblies and Projected Tolerance Zones
Tolerancing Mating Parts in a Fixed Fastener Assembly for Position Tolerancing; GO Gages; Reading Feature Control Frames; Projected Tolerance Zones for Position Tolerances and How to Measure Them; Referencing Datum Features at MMC/Datum Shift and What it Means

Chapter 14 – Position with Floating Fastener Assemblies
Tolerancing Mating Parts in a Floating Fastener Assembly for Position Tolerancing; Selecting Datum Features; Two Single Segment Position Tolerancing; Calculating Tolerances and Datum Shift

Chapter 15 – Direct vs. Indirect Relationships
Accumulation of Tolerances with Multiple Datum Reference Frames

Chapter 16 – Datum Targets
Flexible Parts; Equalizing Datums; Moveable Targets; Finding the Datum Planes; Fixtures

Chapter 17 – Datum Feature Scheme Choices
Secondary and Tertiary Datum Features of Size; Datum Feature Patterns and Profile; Simultaneous Gaging Requirements; Compound Datum Features of Size

Chapter 18 – Flexible Parts
Temporary Datum Features; Restrained vs. Free State Inspection; Free State Variation in Plastic, Rubber and Sheet Metal Parts; How to Write a Restrained State Note; Fixturing Flexible Parts; Fixturing Step Datum Targets; Tolerancing Automobile Panels

Chapter 19 – Positional Boundary Concepts
Elongated Holes; Tolerancing Hoses, Pipes and Tubes; Positional Boundary Concept with Profile of a Surface; An Oddly Configured Hole as a Datum Feature and How to Gage It; Measurement of Tolerance Zones vs. Measurement of Positional Boundaries

Chapter 20 – Composite vs. Two Single Segment Positional Tolerancing
Simple and Complex Parts

Chapter 21 –
Why Use GD&T?; Floating Fastener Assemblies; Converting from Plus and Minus Tolerancing to Composite Position Tolerancing; Interpretation of Tolerance Zones; Minimum Wall Thickness Calculations; Tolerance Stack-Up Analysis

Chapter 22 – Dimensioning and Tolerancing of Gages per the ASME Y14.43-2003 Dimensioning and Tolerancing Principles for Gages and Fixtures standard –
GO Gages; NOGO Gages; Functional Gages; Absolute Gage Tolerancing; Practical Absolute Gage Tolerancing; Optimistic Gage Tolerancing; Tolerant Gage Tolerancing; Calculations that Determine the Possibility of Accepting No Bad Parts, Rejecting No Good Parts or Straddling the Line

Chapter 23 – Statistical Tolerancing and Its Specificity
How to be Specific in Calculating and Specifying Statistical Requirements for Size and Geometric Tolerancing; Symbology for SPC Formulas; Arithmetic Mean; Normal Distribution of Tolerance and the Standard Deviation; Statistical Probability for Tolerance Stack-Up Analysis for Geometric Tolerances

Chapter 24 - Tolerance Stack-Up Analysis
Fixed Fastener Assembly using Geometric Tolerances (a step-by-step tutorial); Main Rules; Calculating Gaps; Working the Route; Calculating Inner and Outer Boundary Means and their Tolerances; Numbers Charts; Calculating Statistical Tolerances; Calculating Tolerances likely to be Consumed by Manufacturing within Six Sigma; The Root Sum Square Formula; The Bender Factor; Monte Carlo Methodology; Reintegrating the Statistical Tolerance into the Assembly; Glossary of Statistical Terms

Chapter 25 – Tolerance Stack-Up Analysis Explanation for a 5-Part Rotating Assembly
Determining Pertinent Factors; Excluding Non-Pertinent Geometric Controls; Simplifying the Assembly Drawing; Graphing the Results; Determining Minimum Gaps or Maximum; Interferences in the Assembly; Wall Thickness Calculations; Choosing the Pertinent Tolerances and Boundaries for Inclusion

Single Part Analysis; Tol. Stack with Profile Tolerance and Separate Requirements; Accumulating Tolerance Error caused by Different Datum Structures

Chapter 26– Tolerance Stack-Ups Created During Manufacture of Products due to Changing Set-ups
Machine and other Manufacturing Capabilities; Trigonometric Factors

Chapter 27 – GD&T as a Language
How to Read Feature Control Frames; Switching Datums- Affects on Gaging, Fixturing and Accumulating Tolerance Error; Different Tolerancing Approaches; Datum Shift; PC Boards; Simultaneous vs. Separate Requirements; Angular Orientation; Datums; Stationary vs. Sliding Gaging Elements; Profile; Tolerance Zones and Pattern Shift; Gear Drawings; Keyways; Bonus Tolerance; Sequential Tolerancing Techniques using the Simultaneous Requirement Rule

Chapter 28 – Definitions

BEST BOOK TO STUDY DIFFERENCES-WELL WORTH TIME AND $$$

I think ISO 8015 Canceled & Replaced by ISO 286-1 1988

 

[dgallup]

"I think ISO 8015 Canceled & Replaced by ISO 286-1 1988"

I do not think that is a true statement. ISO still sell 8015:1985. Per their site:
"Specifies the principle of the relationship between dimensional tolerances and geometrical tolerances. It shall be applied to linear dimensions and their tolerances, angular dimensions and their tolerances and geometrical tolerances which define the following four aspects for each feature of the part: size form, orientation, and location. Refers to ISO 286/1, ISO 1101, and ISO 2692."

 

[Brandy7]

Clarification/Explanation
Former Practice, Important Changes & Consequences

ISO 286-1:1988 clause 5.3.2 states:

For drawings which do not have notation "Tolerancing ISO 8015", the default case for tolerances of the ISO system of limits and fits is the type "Two-point size and mating size".

This means that form was controled by indication of size. This has been changed with this standard into the default rule:
The default definition of size is two-point size.

That means that form is no longer controlled by the indication of size.

Information of Important Changes & the Basis of Former Pactice.

The detailed understanding of linear size for a feature of size and the indication on the drawing was previously given in ISO 286-1:1988, ISO/R 1938:1971 and ISO 8015:1985.

This International Standard changes the above default defination for linear size for a feature of size to two-point size (see clause 5).
This Standard refers to a new edition of ISO 286-1 and it cancels and replaces all clauses and content related to linear dimensions in ISO 8015:1985 (i.e. 1,2, part 3 and the total clauses 4,5.1.1, 5.2, 6 and 7).
The use of reference to ISO 8015:1985 to control size on new drawings, toleranced according to this International Standard, is no longer possible because the use was based on former default definition of size. The new definition for size in this Standard, two-point size, is equal to the use of ISO 8015:1985 and the statment "Tolerancing ISO 8015" on the drawing. Per James D. Meadows book:
Differences and Similarities between ASME & ISO Dimensioning and Tolerancing Standards 2006.

This book compares the most important differences and similarities between the ASME Y14.5M-1994 dimensioning and tolerancing standard and ISO standards and technical reports on dimensioning and tolerancing practices. Unlike other products similar to this on the market, all references in this book from ISO and ASME standards are absolutely up to date as of October 2006. Since many of the most important ISO documents used in the writing of this text were issued in 2004 or later, don’t make the mistake of purchasing out-of-date booklets on this topic.

IMO-BEST BOOK TO STUDY DIFFERENCES-WELL WORTH TIME AND $$$

 

[dgallup]

Well, somebody should tell ISO because they still list 8015 as stage 90.93: International Standard confirmed. It has not been canceled or replaced. I think Mr James D Meadows is a little less authoritative than he thinks he is.

 

[johnson3]

I work for a German company and they utilize ISO 2768, but not well. We presented our case to Management, and were allowed to process our drawings and models in the US to ASME Y14.5M-1994, and are working towards ASME Y14.41-2003. I have a booklet I can scan for you with the differences in the specifications. We have a GD&T study group in our facility 2 days a week, and it is growing rapidly. I am ASME GDTP Senior Certified, and have 2 more Technologists in our group, so we will help where we can. Send me an e-mail and I can get you some information.

 

[Brandy7]

johnson3 (Mechanical)

Please scan and post if you can-It may help many.

 

[joebk]

I have had to deal with the differences between the ISO and ASME systems for a long time. I find that having the standards and studying them helps but applying them here in the US doesn't seem to work well. The two systems have fundamental differences that can result in problems. This seems to be especially true due to the general level of knowledge regarding the proper use of GD&T.

Luckily we are allowed to specify our own standards (ASME) here in the US division but we still have to deal with the ISO system for European designs.

ISO 2768 - I am not going to pull any punches on this one. Sorry this is long but I gotta get this out of my system (still got the venom Kenat). I agree with Kenat - this train wreck is a license for engineers/designers to be lazy.

I have had no end of troubles with this so-called standard. This causes QA and design problems for us all the time. Imagine a QA person trying to verify a part and having to determine what GD&T specifications apply that are not on the drawing (including datums)! This is a waste of time.

When we do inspect parts according to the imaginary GD&T and find problems we generally put the parts on hold with the intention of rejecting them. Of course any supplier (including our parent company) who has some experience with 2768 will pull the following from the standard - "Unless otherwise stated, workpieces exceeding the general geometrical tolerance shall not lead to automatic rejection provided that the ability of the workpiece to function is not impaired". To me, this one statement invalidates ISO 2768.

Basically what I get from this is that there is an implied requirement that doesn't apply if the part still functions. So there are implied tolerances with implied datums that might or might not be more stringent than required?! Why not just state the stinking requirement so there is no question?

I must admit I do like one aspect of ISO 2768. The tolerances are generally based on feature size and not the number of decimal places. I personally prefer this method.

I get wound up when commenting on this standard so it is probably best to just shut my mouth and be done.

 

[KENAT]

Here here joebk.

Like I said using it as a guide for determining what tolerance is readily achievable for certain feature size and 'precision' of machine shop has potential.

Just invoking it as is has some potentially major flaws, but makes it easy for lazy designers/engineers.

My previous comment:

I still think that the last paragraph of the standard basically tells you the standard is meaningless but others disagree.

was with regard to:

Unless otherwise stated, workpieces exceeding the general geometrical tolerance shall not lead to automatic rejection provided that the ability of the workpiece to function is not impaired

Ridiculous.


KENAT, probably the least qualified checker you'll ever meet...

 

[GMIracing]

Thanks everyone for sharing your experiences. I find little comfort in knowing that I have not been alone in finding problems with this ISO 2768 General Tolerance. I also find myself getting a little wound up any time this standard is mentioned or referenced, and being the only EU foreigner in an all German office and all German supplier base, I don't have much support when confronting the holes in the standard.

I will give the Meadows book a chance. Whether he is “Authoritative” or not, I think his book is a better alternative than investing 516 CHF worth into ISO handbooks. Handbooks which may not contain every relevant standard governing the vast (and complicated) ISO Geometrical Product Specifications (GPS).

I came across this Article wrote by Don Day at Tec-Ease, and I thought I would share it: (not my intention to plug or advertise, but I found it relevant to the thread)

http://www.tec-ease.com/the-new-gd&t-article.htm

As an American trained to ASME, I feel this short Article helped me fill in a couple of blanks I was having between ASME and ISO.

I hope johnson3 returns and can provide a little more regarding his booklet and some insight over his proposal he sent to his Management. I will likely have to do the same when returning to our Stateside offices.

 

[dgallup]

Nice link GMIracing. I especially like the following passage:

"ISO 2768 invokes a set of general tolerances based on a study of common machine shop practices. If the part does not meet these general tolerances, the part might still be accepted if it seems to work in its' function. This approach may work in Europe, but with our present requirements for Cp and Cpk, it would never fly. Avoid referencing this standard."

 

[KENAT]

"Avoid referencing this standard." I hadn't looked at the link before (although I've got the standard) but couldn't agree more! I'm glad someone who presumably knows what they're on about agrees with me!

KENAT, probably the least qualified checker you'll ever meet...